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AS 2834—1995
Australian Standard
Computer accommodation
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This Australian Standard was prepared by Committee IT/2, Computer Installations.It was approved on behalf of the Council of Standards Australia on 9 May 1995 andpublished on 5 August 1995.
The following interests are represented on Committee IT/2:
Air-conditioning and Refrigeration Equipment Manufacturers Association ofAustralia
Australian Bankers Association
Australian Construction Services
Australian Fire Authorities Council
Australian Information Industry Association
Australian Institute of Refrigeration, Air-conditioning and Heating
Commonwealth Fire Board
Electricity Supply Association of Australia
National Library of Australia
Review of Australian Standards.To keep abreast of progress in industry, Australian Standards are subjectto periodic review and are kept up to date by the issue of amendments or new editions as necessary. It isimportant therefore that Standards users ensure that they are in possession of the latest edit ion, and anyamendments thereto.
Full details of all Australian Standards and related publications wil l be found in the Standards AustraliaCatalogue of Publications; this information is supplemented each month by the magazine ‘The AustralianStandard’, which subscribing members receive, and which gives details of new publications, new edit ionsand amendments, and of withdrawn Standards.
Suggestions for improvements to Australian Standards, addressed to the head off ice of Standards Australia,are welcomed. Notif ication of any inaccuracy or ambiguity found in an Australian Standard should be madewithout delay in order that the matter may be investigated and appropriate action taken.
This Standard was issued in draft form for comment as DR 93223.
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AS 2834—1995
Australian Standard
Computer accommodation
PUBLISHED BY STANDARDS AUSTRALIA(STANDARDS ASSOCIATION OF AUSTRALIA)1 THE CRESCENT, HOMEBUSH, NSW 2140
ISBN 0 7262 9834 4
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AS 2834— 1995 2
PREFACE
This Standard was prepared by the Standards Australia Committee IT/2 on ComputerInstallations to supersede AS 2834—1985.
This Standard is based on the requirements of computer technology at the time of preparation.However, it is recognized that this technology is rapidly changing and the requirements inthis Standard may be subject to further development.
The objective of this Standard is to provide a guide to requirements for the accommodationof computer equipment. The wide diversity of equipment configurations possible and the wayin which these alter to meet changing technology or system demands make it very difficultto create a simple Standard which is universally applicable. This Standard contains manyrecommendations which should be understood fully by both user and supplier so that earlyagreement can be reached on requirements for the specific installation being considered.
Copyright STANDARDS AUSTRALIA
Users of Standards are reminded that copyright subsists in all Standards Australia publications and software. Except where theCopyright Act allows and except where provided for below no publications or software produced by Standards Australia may bereproduced, stored in a retr ieval system in any form or transmitted by any means without prior permission in writ ing fromStandards Australia. Permission may be conditional on an appropriate royalty payment. Requests for permission and information oncommercial software royalties should be directed to the head off ice of Standards Australia.
Standards Australia will permit up to 10 percent of the technical content pages of a Standard to be copied for use exclusivelyin-house by purchasers of the Standard without payment of a royalty or advice to Standards Australia.
Standards Australia wil l also permit the inclusion of its copyright material in computer software programs for no royaltypayment provided such programs are used exclusively in-house by the creators of the programs.
Care should be taken to ensure that material used is from the current edition of the Standard and that it is updated whenever theStandard is amended or revised. The number and date of the Standard should therefore be clearly identif ied.
The use of material in print form or in computer software programs to be used commercially, with or without payment, or incommercial contracts is subject to the payment of a royalty. This policy may be varied by Standards Australia at any time.
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3 AS 2834— 1995
CONTENTS
Page
SECTION 1 SCOPE AND APPLICATION1.1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3 REFERENCED AND RELATED DOCUMENTS . . . . . . . . . . . . . . . . . . . . 41.4 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.5 CLASSIFICATION OF ENVIRONMENT TYPES . . . . . . . . . . . . . . . . . . . . 91.6 DOCUMENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
SECTION 2 ENVIRONMENTAL REQUIREMENTS2.1 FLOORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2 WALLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.3 CEILINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.4 LIGHTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.5 DOORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.6 FIRE PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.7 VENTILATION AND AIRCONDITIONING . . . . . . . . . . . . . . . . . . . . . . . 122.8 ACOUSTIC CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.9 VIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.10 FURNITURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.11 STATIC ELECTRICITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.12 SITE SECURITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
SECTION 3 ELECTRICAL REQUIREMENTS3.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2 COMPUTER EQUIPMENT POWER REQUIREMENTS . . . . . . . . . . . . . . 183.3 COMPUTER EQUIPMENT EARTH REQUIREMENTS . . . . . . . . . . . . . . . 203.4 ELECTROMAGNETIC COMPATIBILITY . . . . . . . . . . . . . . . . . . . . . . . . 203.5 LIGHTNING PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
APPENDICESA GUIDELINES FOR FACILITY DESIGN OF COMPUTER
INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23B GUIDELINES FOR DESIGNING FLOORING FOR COMPUTER
INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29C GUIDELINES FOR DESIGNING AIRCONDITIONING FOR
COMPUTER INSTALLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34D GUIDELINES FOR THE CONTROL OF STATIC ELECTRICITY . . . . . . . . 38E GUIDELINES FOR IMPROVING THE QUALITY OF COMPUTER
ELECTRICAL POWER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Originated as AS 2834 — 1985.Second edition 1995.
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AS 2834— 1995 4
STANDARDS AUSTRALIA
Australian Standard
Computer accommodation
S E C T I O N 1 S C O P E A N D A P P L I C A T I O N
1.1 SCOPE This Standard sets out the requirements and recommendations for theaccommodation of computers in buildings. It is not intended for application to—
(a) personal or home computers;
(b) remote computer terminals;
(c) equipment of similar construction (unless so specified by the supplier); or
(d) equipment located on factory floors, in public access areas, in the open air or in similaruncontrolled environments.
1.2 APPLICATION It is intended that this Standard be used as a basis for planning acomputer installation. Where recommendations given are not adopted in a design orconstruction, documented reasons should be included in a project file.
This Standard may be applied to existing installations at the time of renovation or extension.
NOTE: Appendix A gives guidance on facility design.
1.3 REFERENCED AND RELATED DOCUMENTS
1.3.1 Referenced documentsThe following documents are referred to in this Standard:
AS1020 The control of undesirable static electricity
1132 Methods of test for air filters for use in air conditioning and general ventilation1132.5 Part 5: Determination of arrestance efficiency, average arrestance efficiency, dust-
holding capacity, and dust-holding capacity per unit of effective face area for testdusts Nos 1, 2 and 3
1170 Minimum design loads on structures (known as the SAA Loading Code)1170.1 Part 1: Dead and live loads and load combinations
1307 Surge arrestors (diverters)
1324 Air filters for use in air conditioning and general ventilation
1428 Design for access and mobility
1530 Methods for fire tests on building materials, components and structures1530.4 Part 4: Fire-resistance test of elements of building construction
1668 The use of mechanical ventilation and airconditioning in buildings1668.2 Part 2: Mechanical ventilation for acceptable indoor-air quality
1670 Automatic fire detection and alarm systems —System design, installation andcommissioning
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AS1680 Interior lighting1680.1 General principles and recommendations1680.2.2 Part 2.2: Office and screen-based tasks1680.2.3 Part 2.3: Educational and training facilities
1735 Lifts, escalators, and moving walks (Known as the SAA Lift Code)1735.11 Part 11: Fire-rated landing doors
1768 Lightning protection
1850 Portable fire extinguishers—Classification, rating and performance testing
1851 Maintenance of fire protection equipment
1905 Components for the protection of openings in fire-resistant walls1905.1 Part 1: Fire-resistant doorsets
2107 Acoustics—Recommended design sound levels and reverberation times forbuilding interiors
2118 Automatic fire sprinkler systems (Known as the SAA Code for Automatic FireSprinkler Systems)
2201 Intruder alarm systems
2293 Emergency evacuation lighting in buildings2293.1 Part 1: Design and installation
2444 Portable fire extinguishers—Selection and location
2926 Standard voltages—Alternating (50 Hz) and direct
3000 Electrical installations—Buildings, structures and premises (known as the SAAWiring Rules)
3080 Telecommunications installations—Integrated communications cabling systemsfor commercial premises
3590 Screen-based workstations3590.2 Workstation furniture
4154 General access floors (elevated floors)4155 Test methods for general access floors4155.6 Method 6: Test for floor resistance for electrostatic control
4214 Gaseous fire extinguishing systems
AS/NZS1044 Limits and methods of measurement of radio interference characteristics of
household electrical appliances, portable tools and similar electrical apparatus
1052 CISPR specification for radio interference measuring apparatus and measurementmethods
ASTM2240-86 Test Method for Rubber Property—Durometer Hardness
AIRAH Design Data Book
Building Code of Australia
1.3.2 Related documents Attention is drawn to the following related documents:
AS1188 Radio transmitters and similar equipment—Safe practices
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AS 2834— 1995 6
AS1603 Automatic fire detection and alarm systems1603.1 Part 1: Heat detectors1603.2 Part 2: Point type smoke detectors1603.4 Part 4: Control and indicating equipment
2107 Acoustics—Recommended design sound levels and reverberation times for buildinginteriors
2743 Stabilized power supplies—a.c. output
2785 Suspended ceilings—Design and installation
1.4 DEFINITIONS For the purpose of this Standard, the definitions below apply.
1.4.1 Airconditioning
1.4.1.1 Air plenum—enclosed volume of supply air under higher than ambient pressure usedin some airconditioning systems to provide forced ventilation.
1.4.1.2 Ambient air temperature—temperature of the air in or around a building.
1.4.1.3 Commercial grade airconditioning—term applied to an air conditioning plant thatis designed for specific applications, usually the conditioning of office and commercialpremises.
1.4.1.4 Computer room airconditioning—term applied to commercial grade airconditioningspecifically designed for use in computer areas.
1.4.1.5 Dehumidification—process of removing moisture from the air.
1.4.1.6 Environment type—classification of a computer room or computer area accordingto the total sensible heat load of its contents and the environmental requirement of the mostcritical device therein.
1.4.1.7 Humidification—process of adding moisture to the air.
1.4.1.8 Latent heat—heat that does not affect the temperature of a substance but changesthe state when added to or removed from it.
1.4.1.9 Relative humidity (RH)—ratio of the actual water vapour pressure of the air to thesaturated water vapour pressure of the air at the same temperature.
1.4.1.10 Sensible heat—heat that changes the temperature of a substance when added to orremoved from it.
1.4.1.11 Sensible heat factor—ratio of sensible heat to total heat.
1.4.1.12 Supply air—air introduced into an enclosure by mechanical means.
1.4.1.13 Total heat—summation of sensible and latent heat.
1.4.1.14 Vapour barrier—barrier which is impervious to the transmission of moisture.
1.4.2 Building elements
1.4.2.1 Acoustically treated wall—wall which has been treated with materials to enhancethe sound absorption or sound isolation of the wall, or both.
1.4.2.2 Acoustic ceiling—ceiling which has enhanced sound absorption or sound isolation,or both.
1.4.2.3 Computer area—space within a building which houses a computer system,associated media storage and support services and includes, where provided, the computerroom.
NOTE: The term ‘computer area’ is assumed to refer to one continuous area, sections of which mayor may not be independently sealed for the purposes of fire protection or the environment, or both.
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1.4.2.4 Computer room—room whose sole function is to house a computer system andprovide the required operating and non-operating environment.
1.4.2.5 Concentrated live load—load concentration presented by each foot or wheel of eachunit.
1.4.2.6 Elevated floor(also known as access floor, false floor or raised floor)—type offlooring that creates a void or space above the structural floor, to be used to route and protectcables or create a plenum for air distribution, or both. (See Figure 1.1).
1.4.2.7 Finished ceiling height—height from finished floor height to the underside of thefinished ceiling.
1.4.2.8 Finished floor height—height from the top of the structural floor to the top of thefloor on which equipment will be installed.
1.4.2.9 Fire door—doorset, single or multileaf which, except when varied as permitted byAS 1735.11 or AS 1905.1, is identical in assembly, construction and installation with aprototype that has established its fire-resistance when submitted to a fire test as set out inAS 1530.4.
1.4.2.10 Fire-resistant wall—wall, either loadbearing or non-loadbearing, capable ofsatisfying for stated periods the criteria of fire resistance with respect to stability, integrityand thermal insulation.
1.4.2.11 Luminaire—light fitting which distributes, filters or transforms the light given bya lamp or lamps.
1.4.2.12 Solid floor—normal structural floor onto which elevated floors can be installed orthe computer system itself may be positioned.
1.4.2.13 Stringers—structural cross-members of an elevated floor that form a grid and giverigidity and strength to the floor’s construction.
1.4.2.14 Structural floor—loadbearing building element providing the lower horizontalsurface of a building space.
(a) Underfloor clerance where support structureis lowest element
(b) Underfloor clearance where part of floor panelprotrudes below support structure
FIGURE 1.1 FLOOR HEIGHT AND UNDERFLOOR CLEARANCE
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AS 2834— 1995 8
1.4.2.15 Suspended ceiling—ceiling forming a void which may accommodate services suchas electrical and data cables, fire services, airconditioning services, plumbing, or form aplenum for air delivery or return.
1.4.2.16 Underfloor clearance—distance between the top surface of the structural floor andthe underside of the support structure or panels of the elevated floor.
1.4.3 Electrical
1.4.3.1 Bulk resistance—resistance of a material measured between a specified electrodeplaced on the surface of the sample and the safety earth of the building.
1.4.3.2 Decibel—scale unit used in the comparison of voltages or currents. The number ofdecibels is 20 times the logarithm to the base 10 of the ratio of the voltages or currents.
NOTE: Electrical noise attenuation by any device is given as the ratio of the input to output noisevoltages expressed in decibels.
1.4.3.3 Dedicated line—separate set of power conductors, plus a dedicated safety earth,routed directly from the building’s main switchboard, major distribution panel or computerline conditioner to the computer system distribution panel or to the computer equipmentitself. Only computer equipment may be connected to it.
1.4.3.4 Dedicated safety earth—separate safety earth system which ideally has a singleconnection to the safety earth, and which features insulated conductors presenting a lowimpedance to earth for high frequency noise. It is normally used to earth only computerequipment.
1.4.3.5 Earth loop—condition where two or more components in a computer system haveearth points connected together by two or more conductor paths.
NOTE: Cyclic noise currents may be generated in the loops so formed.
1.4.3.6 Harmonic voltage distortion(Un)—r.m.s. value of a harmonic voltage, of ordern,expressed as a percentage of the r.m.s. value of the fundamental.
1.4.3.7 Safety earth—electrical installation earthing system to which are connected partsthat are earthed in accordance with AS 3000.
1.4.3.8 Surface resistance—resistance of a sample measured between two specifiedelectrodes placed a nominated distance apart on the surface of the sample.
1.4.3.9 Total harmonic voltage distortion(Ur) —calculated from the expression—
and expressed as a percentage of the fundamental.
NOTE: Generally, it is sufficient to use values ofn up to 25.
1.4.4 Fire protection
1.4.4.1 Fire detector—device which gives a signal in response to a predetermined changein one or more ambient conditions in the vicinity or within the range of the detector, due toa fire.
1.4.4.2 Gas flooding system—gas fire extinguishing system that has a total blanketing effectwithin a confined area.
1.4.4.3 Manual override—an option available to prevent gas flooding systems fromoperating unnecessarily.
1.4.5 Organizations
1.4.5.1 Equipment supplier—the organization that supplies units of computer equipment.
1.4.5.2 User—the organization that uses the computer system.
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1.4.6 Vibration—regular or impulse-type mechanical movement transmitted to thecomputer equipment from the external environment. It may be of varying amplitudes andfrequencies.
1.5 CLASSIFICATION OF ENVIRONMENT TYPES Computer equipment shall beclassified by the suppliers in accordance with the environment type in which the units aredesigned to operate. Information on airconditioning requirements for these environment typesis given in Clause 2.7. The environment types are as follows:
(a) Environment Type 1 Computer room in which tight control is maintained overtemperature, humidity and air quality. It has an airconditioning system, usually withstandby capacity. Access to the computer room is limited to essential personnel, andeating, drinking and smoking are prohibited. Limited access provides a measure ofsecurity, but also keeps the ingress of unfiltered, unconditioned air and contaminantsto a minimum. An elevated floor is recommended and, in some cases, the supplier mayrequire it.
(b) Environment Type 2 Computer room in which either all or the most critical parts ofa computer system are installed. It has an airconditioning system to ensure proper andefficient cooling and filtration, although the requirements are not as strict as forEnvironment Type 1. An elevated floor may be installed, but is usually not warranted.The room may have limited accommodation for operations staff, and the equipmentmay operate unattended.
(c) Environment Type 3 Typically, an airconditioned office that can handle small amountsof computer equipment provided that the total heat load does not exceed the capabilityof the office airconditioning to maintain the optimum conditions. Air filtration isgenerally less efficient and there is the risk of contamination from food, drink andsmoke.
NOTES:
1 In practice, there are large variations in office conditions, e.g. small room with a door ora large open-plan area. Some parts of the office may have adequate air flow for heatremoval, whereas other parts may become ‘hot-spots’ owing to the build-up of heatgenerated by the equipment.
2 If there is doubt that the system will operate efficiently in an Environment Type 3, all orpart of the equipment should be classified as suitable for use in Environment Type 2.
(d) Environment Type 4 Typically, an office environment that has no airconditioning,except possibly for heating in winter. It is generally suitable only for equipment whichproduces little heat, such as small terminals.
NOTE: If the equipment heat output is high, the room temperature may rapidly rise beyond theupper limit of the operating range, the maximum rate of change may be exceeded and theenvironment could become uncomfortable for the office staff.
1.6 DOCUMENTATION Operating and maintenance instructions for all plant andequipment shall be part of all goods supplied.
For an airconditioning plant, instructions shall include design data, field commissioning testresults, fluid flows and temperatures, as-installed drawings as well as plant item locationswhere these are not immediately obvious.
NOTE: It is strongly recommended that all such instructions, results and drawings are retained onsite so that they may be made available when maintenance or future system expansion is beingconsidered.
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AS 2834— 1995 10
S E C T I O N 2 E N V I R O N M E N T A LR E Q U I R E M E N T S
2.1 FLOORS
2.1.1 General Floors shall be one of the following types:
(a) Elevated.
(b) Solid.
NOTES:
1 This Clause is intended to be applied primarily to Environment Types 1 and 2, but may haveapplication to Environment Types 3 and 4.
2 Refer to Appendix A for details relating to vapour barrier requirements.
3 Appendix B gives guidelines for the design of floors.
2.1.2 Conductivity The surface of the floor shall provide a limited electrical conductivitybetween all persons and equipment making contact with the floor to prevent the accumulationof undesirable electrostatic charges. In the interests of electrical safety, exposed, earthedmetal shall not appear at the floor surface. For a conductive floor with an earthedundersurface (e.g. an elevated floor with earthed substructure or carpet laid directly on aconcrete slab), the bulk resistance of the floor is its more important resistive property. Wherethe conductive floor is laid over an insulating surface (e.g. carpet on a rubber underlay), thenthe surface resistance is the more important parameter.
The surface or bulk resistance of the floor or floor panels shall be not less than 500 kΩ andnot greater than 20 GΩ when measured in accordance with AS 4155.6.
NOTES:
1 The requirements of this Clause are consistent with good practice when installing or renovatinga floor for computer usage. They may also be specified as mandatory by the suppliers of somecomputer equipment. However, the trend in computer design is towards equipment that is lesssensitive to electrostatic charges. In some cases, therefore, an existing floor that does not meetthe requirements below may, nevertheless, satisfy the requirements of the equipment supplier.
2 The minimum value of 500 kΩ is specified as a protection against electrical shock.
3 The maximum value of 20 GΩ is specified as a protection against the build-up of undesirableelectrostatic charges.
4 Floor coverings that meet these criteria are commercially available.
2.1.3 Elevated floors Elevated floors shall be designed and tested in accordance withAS 4154.
2.1.4 Underfloor clearance The preferred underfloor clearance shall be 300 mm but inno case less than the following:
(a) When used as an airconditioning plenum . . . not less than 250 mm.
(b) When only conduits, small diameter pipes and signal cables are installed . . . not lessthan 150 mm.
NOTES:
1 Any obstructions, which may adversely affect air flow or limit the laying or relocation ofcables, may require minimum underfloor clearances, greater than those stated above.
2 Where adequate ceiling height permits, a minimum underfloor clearance of 300 mm isrecommended. For ceiling height restrictions, see Clause 2.3.1.
3 Some suppliers may have specific requirements.
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2.1.5 Underfloor treatment Where the space beneath the elevated floor is used as an airplenum and the surface of the structural floor is concrete, the structural floor shall be sealedto prevent dust and moisture ingress. Other types of structural surface should be treated asrequired to provide a firm and non-contaminating surface.
2.1.6 Earthing of elevated floors Metal components of the elevated floor substructureshall be securely connected to safety earth in order to earth the entire elevated floor sub-surface effectively. The resistance between such metal components of the elevated floor andearth shall not exceed 1Ω.
2.1.7 Solid floors Solid floors shall be capable of withstanding the applied loads (existingand anticipated).
NOTE: For determining loads, see AS 1170.1.
2.2 WALLS All perimeter walls, enclosing computer rooms requiring an EnvironmentType 1 or Type 2 and all storage areas that share the same environment, shall be constructedso as to extend from the structural floor to the underside of the roof or the underside of thestructural floor of the next storey, as appropriate, to ensure the integrity of thermal andvapour barriers.
NOTES:1 See Appendix A in relation to vapour barrier requirements.
2 The type of wall construction and materials used will generally depend on exposure, securityrequirements, fire resistance, dust suppression, vapour sealing, sound transmission andenvironmental and building codes.
2.3 CEILINGS2.3.1 Ceiling height The minimum ceiling height shall comply with the requirements ofthe regulatory authority. Greater ceiling heights may be required if—
(a) the equipment supplier specifies a greater height; or
(b) additional space is required for airconditioning ductwork, cable trays, sprinkler headclearance, and the like.
2.3.2 Material Suspended ceilings and their linings shall be non-combustible as requiredby the regulatory authority. Linings should not give rise to the production of dust. Non-combustible mineral fibre or fibreglass filling inserted in ceiling tiles (e.g. for acoustic or airbalancing reasons) shall be contained in sealed bags of minimal fire-propagating properties.
NOTES:1 Some sprayed ceiling finishes, insulating materials and the damaged edges of ceiling tiles may
shed dust or particles.2 Acoustic properties of a ceiling should be considered.
3 If the ceiling is of concrete, the surface should be sealed to prevent dust and moisture ingress.4 See Appendix A in relation to vapour barrier requirements.
2.3.3 Cable trays Where a significant quantity of cables are to be laid over a suspendedceiling, the use of earthed cable trays, fixed to the building structure, is recommended.
2.4 LIGHTING
2.4.1 General Lighting shall comply with the requirements of AS 1680.1, AS 1680.2.2,and AS 1680.2.3, as applicable.
NOTES:1 Modern office buildings normally have a fixed grid of ceiling luminaires throughout, which are
designed to provide uniform illumination in accordance with AS 1680.1. The installation ofequipment, such as a row of tall computer cabinets, could disrupt the uniformity. This situationcan be avoided by taking existing lighting into consideration when designing the equipmentlayout and by the provision of local lighting.
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AS 2834— 1995 12
2 Where lighting does not already exist, it may be designed to fit in with the layout in order tomeet the requirements of this Clause.
3 Users and designers should ensure that the lighting is adequate in areas where service personnelwill be required to work particularly in underfloor areas. Local (task) lighting may be required(see Clause 2.4.2).
2.4.2 Local lighting Notwithstanding Clause 2.4.1, the equipment supplier may requirea higher level of illumination to be associated with certain equipment. This may be providedthrough local lighting in accordance with AS 1680.1. In such cases, the supplier shall providedetails of the location and level of the illumination required.
2.4.3 Unwanted reflections Care shall be taken when designing equipment layout andlighting to avoid unwanted reflections which would interfere with the visual efficiency orcomfort of computer room personnel.
NOTES:
1 AS 1680.1 gives guidance on dealing with unwanted reflections.
2 Particular note should be taken of reflections from equipment viewing windows, especiallyinclined or horizontal windows such as often found on printers.
2.4.4 Emergency evacuation lighting When required by the regulatory authority, or tomeet insurance requirements, the emergency evacuation lighting system shall comply withAS 2293.1.
2.5 DOORS Access doors into the computer area shall be of adequate width and heightto allow convenient movement of computer and associated equipment. Doors shall not beunder-cut or fitted with grilles. The fire resistance shall be equal to the surrounding wallconstruction.
NOTES:
1 See Appendix A for guidance on accessibility.
2 Where existing door sizes are found to be adequate, no changes are recommended. However,for new computer rooms and where existing doors require replacement, a door width giving aclear opening of 900 mm or larger is recommended.
2.6 FIRE PROTECTION Computer areas with Environment Types 1 and 2 and areasunder an elevated floor and above a false ceiling shall be provided with a fire protectionsystem encompassing detection and suppression.
Fire detection systems, where provided, shall comply with AS 1670. Sprinkler installations,where fitted, shall comply with AS 2118. Fire extinguishing systems using gaseoussuppressants shall comply with the relevant parts of AS 4214.
Computer rooms shall be provided with portable fire extinguishers, the ratings, quantity anddistribution of which shall be in accordance with AS 1850 and AS 2444.
NOTE: All fire protection equipment should be installed and maintained in accordance with theappropriate parts of AS 1851 and the Building Code of Australia.
2.7 VENTILATION AND AIRCONDITIONING
2.7.1 General Ventilation systems within computer areas shall comply with AS 1668.2,where applicable.
NOTE: See Appendix C for guidelines on airconditioning systems and information on theparticulate and chemical contamination of fresh air.
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2.7.2 Environmental conditions
2.7.2.1 Maximum sensible heat load of systemIndividual units may be rated by theequipment supplier to operate in a particular environment type. Notwithstanding thisindividual rating, if such a piece of equipment is connected with other equipment of a higherrating, or if the total heat load of a number of similarly rated units exceeds the capacity ofthe relevant environment, then the system as a whole should to be promoted to a higherrating.
NOTES:
1 The ‘maximum sensible heat load of system’ in Table 2.1 is intended as a guide to indicatewhich type of environment would be the most suitable in such circumstances.
2 As stated in Clause 1.5, Items (c) and (d), the maximum heat handling capabilities of someenvironments are subject to wide variations. Hence, the values in Table 2.1 for EnvironmentTypes 3 and 4 are typical only, and may vary according to circumstances.
2.7.2.2 Temperature and relative humidity rangesTable 2.1 specifies the requirement foreach type of environment. Equipment shall always be operated at the optimum temperatureand relative humidity. The operating ranges are intended solely as a short-term emergencybuffer in the event of airconditioning failure.
NOTE: Operation outside the operating ranges, or for long periods above or below optimumconditions, may produce the following effects:
(a) Stressing or premature ageing of some components, leading to premature or intermittentfailures. Often these problems do not manifest themselves until several weeks or months afterthe event.
(b) Electrical contact problems.
(c) Static electricity problems.
The upper operating temperature limits specified in Table 2.1 are effective up to an altitudeof 500 m above mean sea level. Above 500 m, the upper limit is derated linearly to 2500 m(the highest land-based altitude in Australia) by a value of 2°C per 1000 m. This is due tolower atmospheric pressure and air rarefaction affecting cooling capabilities.
EXAMPLE: An Environment Type 2 sited at an altitude of 2000 m would require an upperoperating temperature limit derated to 29°C.
2.7.2.3 Condensation Condensation shall never be permitted to occur in any computerenvironment (unless specifically permitted by the equipment supplier).
NOTE: If an Environment Type 4 is operating simultaneously at high temperature and high relativehumidity, relatively small changes in temperature can cause condensation to occur. Consequently,equipment in these environments should not be operated in such conditions.
This problem should not occur with Environment Types 1, 2 or 3 provided that they are maintainedwithin their specified limits.
2.7.2.4 Optimum temperature and relative humidityThe ranges of optimum temperatureand relative humidity are those over which most computer equipment operates most reliablyfor long periods. Where airconditioning is used, it shall be designed to maintain theenvironment at the centrepoints of these ranges under all ambient conditions throughout theyear and at all likely loads.
2.7.2.5 Maximum temperature and relative humidity gradientsThe rates of change oftemperature and relative humidity shall not exceed the gradients specified in Table 2.1. Rapidchanges can damage components and media when equipment is operating and, in some cases,may cause condensation.
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AS 2834— 1995 14
TABLE 2.1
REQUIREMENTS FOR ENVIRONMENT TYPES*
CharacteristicsEnvironment type
Type 1 Type 2 Type 3 Type 4
Maximum sensible heat load of system N/A N/A 2000 W 500 W
Operating temp. range 18°C to 26°C 16°C to 32°C 16°C to 32°C 15°C to 35°C
Operating relative humidity range 40% to 60% 40% to 70% 40% to 70% 20% to 80%
Optimum temperature 23±1°C 23 ±2°C 23 ±4°C 23 ±4°C
Optimum relative humidity 50±5% 50 ±10% 50 ±10% 50 ±10%
Maximum temperature gradient 1°C per 10 min 1°C per 6 min 1°C per 6 min 1°C per 6 min
Maximum relative humidity gradient 5% per hour 10% per hour 10% per hour †
Floor plenum condit ions:(a) Minimum temperature(b) Maximum relative humidity
†15°C80%
†15°C80%
N/A N/A
Minimum sett ling period † † 30 min N/A
Filt ration type (AS 1324) Type 1Class A, B
Type 1Class A, B
See Clause2.7.2.8(b)
N/A
Filter minimum efficiency ‡ 20% 20% See Clause2.7.2.8(b)
N/A
* Refer to equipment supplier for non-operating environmental limits.† Due to wide variety of condit ions encountered, it is recommended that appropriate criteria values be agreed upon
between the user and the equipment supplier.‡ In accordance with AS 1132.5, using Test Dust No. 1 or other standard specified by the equipment supplier.
2.7.2.6 Air plenum conditions Where an elevated floor is used as an air distributionplenum, the temperature of the air in the underfloor area shall be no less than and the relativehumidity shall be not greater than the values specified in Table 2.1 at any room-entrylocation, unless otherwise specified by the computer equipment supplier.
2.7.2.7 Minimum settling period When an environment has been allowed to go outside theoperating temperature and humidity ranges with the computer equipment turned off (e.g.overnight, weekend), there shall be a settling period after the environment has returned tonormal conditions before power may be applied to the computer equipment. This period isto permit the media and equipment interior conditions to stabilize in the operatingenvironment.
In addition, for Environment Types 1 and 2, the airconditioning should continue to operatefor at least 30 min after computer power-off (or as recommended by the equipment supplier).
NOTES:
1 When airconditioning is first turned on in such circumstances, there will be a rapid change intemperature and relative humidity such that the maximum operating gradients may be exceeded.The airconditioning system should be designed such that condensation cannot occur.
2 To avoid unnecessary delays due to the settling period, a time switch may be fitted to theairconditioning system such that the latter will be switched on and off at the appropriate timesin relation to the scheduled operating times for the computer.
3 A better (and preferred) solution is to operate the airconditioning continuously, even duringweekends when the computer is not turned on. This method avoids the problem of the settlingperiod entirely. With correct system design, running costs are not very much greater. As thereis no load from the system, the airconditioning will be mostly providing ventilation only. Thismethod may not be practicable for Environment Type 3 where an office may be a large openarea or where the main building airconditioning is used to cool the equipment.
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2.7.2.8 Filtration Requirements for filtration are specified as follows:
(a) Environment Types 1 and 2Both environment Types 1 and 2 require strict controlover the cleanness of the air in the computer room. Excessive dust or pollutants candamage both equipment and media.
Care shall be taken to ensure that the room is sealed such that unfiltered air cannotenter when access doors are closed. Doors should be kept closed at all times and accessto personnel restricted.
NOTE: Dust exclusion can be assisted if the airconditioning is adjusted to provide a slightlyhigher air pressure in the computer room than the ambient air pressure, and if doors that arenot normally kept locked are fitted with spring closers.
(b) Environment Type 3 Ideally, Environment Type 3 should have the same order offiltration as Types 1 or 2. If the office is reasonably small (up to 3 or 4 rooms) and isindependently air-conditioned, an adequate degree of filtration can be achieved byusing the same type, class and kind of filters specified for Types 1 and 2.
NOTE: No degree of filtration will be effective unless office personnel are disciplined to keepall external doors and windows closed and to refrain from eating, drinking and smoking in thecomputer area.
Where an Environment Type 3 is supplied from the main building airconditioning, thetype of filtration is usually determined by other criteria.
Should this be considered inadequate, or should other factors in the office affect thecleanness of the environment, it may be necessary to consider upgrading anEnvironment Type 3 to Type 2.
NOTES:
1 The main building airconditioning plant may use filters other than Type 1 filters complyingwith AS 1324. In this case, Test Dust No. 1 of AS 1132.5 may not be applicable. However, anequivalent rating from the appropriate AS 1132 test will suffice.
2 Where Type 3 (electrostatic precipitation) filters complying with AS 1324 are used in theairconditioning of the main or other parts of the building, they should not be located physicallyor electrically near the computer room. This type of filter can electrostatically discharge,possibly creating radiated or conducted electromagnetic interference, or both.
3 Pre-filters may be placed in front of the main filters to increase the effective service life of themain filters. In areas of high pollution, specialized outside air pre-filters may be required toremove the polluting gas or particles. See Appendix C for guidance on contamination levels.
2.7.3 Humidity control Information on the control of humidity is given in Appendix C.
2.7.4 Airconditioning capacity When calculating the required sensible cooling capacityof the computer airconditioning system following an agreed method, the following factorsshall be taken into account:
(a) The total sensible heat output of the computer equipment should be provided by thesupplier.
(b) The total sensible heat output of any other equipment in the area covered by theairconditioning system, e.g. card punches, decollators, power conditioning equipmentand fan loads in process coolers.
(c) Total room load which comprises sensible and latent heat from lighting, personnel andall external sources, including fresh air make-up and, in particular, gain from the sun.The airconditioning supplier or consultant shall calculate this figure, assuming theworst case situation, following an agreed method.
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(d) Minimum and maximum ambient temperature and humidity conditions during the peakof summer and winter, respectively, at the computer site location. This information canbe obtained from the Weather Bureau or the Australian Institute of RefrigerationAir-Conditioning and Heating (AIRAH) Design Data Book.
The airconditioning system shall be designed to maintain the environmental conditionsspecified in Clause 1.5 and Table 2.1 under all ambient conditions throughout the year.Maximum excursions and gradients shall not be exceeded.
NOTES:
1 Airconditioning capacity should be quoted as sensible heat (see Clause 1.4.1.10). Total heat(see Clause 1.4.1.13) is sometimes quoted.
2 People produce both dry heat and moisture (breath and perspiration). Office airconditioning isdesigned to take this into account. Computer equipment outputs are only dry (sensible) heat,consequently selection should be based on sensible cooling capacity and sensible heat factor.
3 The user should advise the consultant or airconditioning supplier of the sensible heat loads andthe room design conditions, and ascertain that the distinctions made in the above notes areproperly understood. Suppliers and consultants who deal mostly with office or factoryairconditioning do not always appreciate the special requirements of computer equipment.
2.8 ACOUSTIC CONSIDERATIONS Computer equipment, airconditioning, line-conditioners and standby power sources all generate acoustic noise which in many cases mayprove disruptive to staff working in the computer room or to people in adjoining premises.The supplier of the computer and other equipment should make available data on the noiseemission of each item of equipment associated with the computer room. Acoustic treatmentof room surfaces may be required to provide a suitable working environment (seeAppendix A and AS 2107).
2.9 VIBRATION Unless otherwise authorized by the equipment supplier, vibration of thecomputer environment shall conform to the following:
(a) Vibration limit 2.5 m/s2 rms overall in the frequency range 3 Hz to 1000 Hz.
(b) Displacement limit 0.254 double amplitude in the frequency range 5 Hz to 22 Hz.
(c) Measurement positionsOn the supporting table or structure alongside each supportor fixing of each item of equipment.
(d) Measurement directions Measurements shall be made in the horizontal plane in thefore and aft or X direction; in the left and right or Y direction; and in the vertical orZ direction.
(e) Operating conditions The equipment of concern shall be not operating, but all otherequipment including other computer equipment, shall be operating. For example, if apersonal computer and an impact printer are on a tabletop, then the vibration of thetable top should be measured alongside the computer with the computer off and theprinter operating in self-test mode.
(f) Test report—personnel, instrumentsVibration measurements shall be made byqualified personnel using appropriate instrumentation. The test report shall list allinstruments used and shall include a description of the instruments and procedures forcalibrating the vibration measurement equipment.
NOTES:
1 The equipment in the computer area (e.g. airconditioning or diskdrives) may be a source ofvibrations.
2 Sensitive equipment can usually be protected by properly selecting off-the-shelf isolatormountings.
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2.10 FURNITURE Computer room furniture should be selected in accordance withAS 3590.2.
NOTE: See Appendix A.
2.11 STATIC ELECTRICITY Static electricity may have an impact on computerequipment and should be controlled in the computer environment.
NOTE: See Appendix D for information on static electricity and Clause 2.1.1 on conductivityrequirements for floors. See AS 1020 for general guidelines on the control of static electricity.
2.12 SITE SECURITY Any security system installed shall comply with the requirementsof the appropriate regulatory authority and the appropriate parts of AS 2201, as necessary.
Security systems may address intruder detection or access control, or both. Detectors shouldbe selected and aimed to minimize false alarms whilst maximizing detection capability.Monitoring at a remote location may be desirable. Unless otherwise specified, systems shouldcomply with the relevant Australian Standards.
Security of any external communications lines should be considered with respect toreliability, and to minimizing interference with, or theft of, data.
NOTE: No other requirements are given in this Standard (see Appendix A).
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AS 2834— 1995 18
S E C T I O N 3 E L E C T R I C A L R E Q U I R E M E N T S
3.1 GENERAL All computer equipment shall be installed in accordance with therequirements of AS 3000 and those of the regulatory authorities.
NOTE: Nothing in this Section is intended to override or supersede any of the above requirements.Rather the intent is to specify additional requirements and precautions to be observed wheninstalling and operating computer equipment.
3.2 COMPUTER EQUIPMENT POWER REQUIREMENTS3.2.1 General Unless otherwise specified by the equipment supplier, computer equipmentshall be provided with a power supply service which meets the criteria specified inClauses 3.2.2 to 3.2.8.
3.2.2 Voltage The r.m.s. voltage supplied to computer equipment shall be designed toremain within the tolerances specified in this Clause at all times during computer equipmentoperation, as follows:
(a) Nominal voltage The nominal voltage of each power phase shall be as follows:
(i) Phase-to-neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 V (+6,−10%).
(ii) Phase-to-phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 V (+6,−10%).
(b) Multiphase supply Where multiple power phases are required, each phase-to-neutralor phase-to-phase voltage shall be within 5% of each other, phase-to-neutral orphase-to-phase voltage.
(c) Neutral voltage The voltage on the equipment neutral conductor (where applicable)with respect to safety earth shall not exceed 5 V as measured at the equipment powertermination. (See Note 3.)
NOTES:
1 Some computer equipment may operate on a different nominal voltage (typically 120 V). Assuch a voltage is not commercially available in Australia, it is usually derived from thecommercial 240 V service, commonly via a transformer. The equipment supplier should providedetails.
2 During site selection or preparation, it is recommended that a power survey be conducted fora minimum continuous period of 10 days. A powerline analyzer, capable of measuring thedynamic supply parameters, should be connected to all power phases at the outlet that isintended to supply the computer equipment. The results of the survey will give the user and theequipment supplier a good idea of the quality of the power service although it cannot guaranteethe future quality. Where the survey results indicate that the requirements of this Section maynot be met, Appendix E gives guidance on steps that may be taken to improve the powerquality.
3 The neutral-to-earth voltage can be a particular problem in the upper floors of high-risebuildings. This is of prime concern with regard to 3-phase equipment. Therefore, this potentialproblem can be an influencing factor in the siting of the equipment or in the use of a dedicatedline as per Clause 3.2.7. High neutral-to-earth voltages can be a fire hazard and a safety hazardto service personnel.
3.2.3 Voltage disturbances A.C. transients on the supply voltage shall be designed not toexceed 7% amplitude of the nominal r.m.s. phase-to-neutral or phase-to-phase voltage anda duration of 10 ms, and shall not occur more frequently than once in every 10 s. A completeloss of voltage shall not exceed 10 ms in duration and shall not occur more frequently thanonce in every 10 s.
NOTES:
1 Installation of a clean line in accordance with Clause 3.2.7 may minimize the effects of localdisturbances.
2 The power survey recommended in Note 3 of Clause 3.2.2 may detect voltage disturbances ofthese kinds.
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3 It is recognized that the requirements of this Clause may not be met at all times on a normally‘clean’ supply, e.g. during electrical storm activity or bushfires. However, it should beunderstood that in such cases, equipment may malfunction and process be disrupted.
4 Appendix E gives guidance on suppressing voltage disturbances.
3.2.4 Frequency Unless otherwise specified by the equipment supplier, the frequency ofpower supplied to computer equipment shall be designed to be 50±0.5 Hz.
NOTES:
1 Some computer equipment may require d.c. or a.c. of a different frequency. Typical alternativefrequencies are 60 Hz and 400 Hz to 440 Hz. It is the responsibility of the equipment supplierto specify the requirements in such cases and to recommend a suitable method for obtaining therequired supply.
2 The electricity supply grids usually provide a stable frequency within the tolerance of thisClause. However, power supplied by private generators or those of smaller towns not connectedto the grid may not be reliable in this respect.
3 The power survey referred to in Clause 3.2.2 should include frequency monitoring.
3.2.5 Voltage distortion Where the total harmonic voltage distortion (THD) of the voltagewaveform exceeds 5% at any time during computer equipment operation, the equipmentsupplier shall be consulted.
NOTE: The quality of the waveform can be approximately assessed by observing it with anoscilloscope. More accurate measurements may be made, if required, with a distortion analyzer ora spectrum analyzer. Normally, these steps would only be taken where there was doubt regardingthe THD.
3.2.6 Phase balancing At multiphase installations, the computer equipment shall beconnected such that, with the system operating in its normal configuration, each power phasedraws approximately equal current. The supplier shall indicate the phase connections mostlikely to result in current balance.
NOTES:
1 No specific tolerances are given for various reasons, e.g. at different times various units ofequipment may not be in operation.
2 It may not be possible for the equipment supplier to predict accurately the optimum currentbalance connections, due to the number of variables.
3.2.7 Dedicated line The following conductors shall be provided from the building’s mainswitchboard either directly to the computer equipment or via one or more of a computersupply distribution panel, transformer and power treatment device (see Appendix E):
(a) One, two or three phases, as required. If fuses are used in multi-phase supplysituations, then a phase failure device that would remove all phases in the event of asingle phase failure may be required.
(b) A neutral conductor, except where only a three-phase delta or a single-phase 415 V (or440 V) service is required. This shall be the same size as the phase conductors.
(c) A dedicated safety earth conductor (see Clause 3.3).
The conductors shall be sized to provide the maximum required load allowing for futureexpansion and should include a factor of at least 60%. (The factor of 60% is suggested toreduce electrical noise and to minimize switching transients which can occur on fully loadedlines.)
Where power conductors are laid in metallic conduit, the conduit shall be connected to thesafety earth system, and not to the dedicated safety earth (see Clause 3.3).
Where required by the equipment supplier, the power conductors shall be shielded by aninsulated and earthed screen. The screen shall be connected to the safety earth.
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AS 2834— 1995 20
Where a dedicated line is provided, no other devices, e.g. computer area lighting andairconditioning, shall be connected to this power service or the computer supply distributionpanel.
NOTES:
1 The purpose of a dedicated line is to minimize the incidence of noise and voltage fluctuationsintroduced into the computer equipment by conduction as a result of the operation of otherdevices within the building.
2 Equipment connected to the power service, via a plug and socket, may be protected fromaccidental disconnection by the installation of an approved locking-type plug and socket.
3 In a high-rise building, it may not be practicable to source the computer power service directlyfrom the main switchboard when the computer equipment is to be installed on an upper floor.In such cases, the service may be sourced from the main distribution panel serving the floorconcerned. Depending on the loading of the power riser, and the sizing and insulation of theearth riser, the computer power service may effectively be a dedicated line. This may bedetermined by conducting a power survey as per Clause 3.2.2, Note 3.
3.2.8 Emergency power-off control Where required, a control which effects totalshutdown of all power to the computer system shall be installed to the equipment supplier’selectrical specifications.
The control shall comply with the following requirements:
(a) Located at an easily accessible place.
(b) Protected against accidental operation but simple to operate, i.e. not requiring specialknowledge or a key.
(c) Prominently labelled with the legend ‘EMERGENCY OFF’ in white letters on a redbackground.
NOTE: It is recommended that all the user’s operations staff be trained in the correct usage of thiscontrol.
3.3 COMPUTER EQUIPMENT EARTH REQUIREMENTS
3.3.1 General All devices powered from the supply mains that are not double-insulatedrequire a connection to safety earth in accordance with AS 3000.
Within a computer system there are common reference points for logic signals. These aresometimes connected to the machine frame within each unit of the system. These frames arein turn connected to safety earth.
In some systems, these common reference points are not connected to the frame of each unitbut are interconnected between units in the system cabling for connection at a single pointwhich is generally also earthed as above.
In either case, it is important that the connection to earth is made as close as practicable toa point in the safety earth distribution system that has the lowest level of conductedinterference from external sources.
3.3.2 Dedicated safety earth connection Where the safety earth connection forms partof the dedicated line it shall comply with the requirements of AS 3000.
3.4 ELECTROMAGNETIC COMPATIBILITY
3.4.1 General Electromagnetic compatibility (EMC) is a measure of the electromagneticrelationship between a unit of electrical equipment and its environment. The equipmentsupplier should provide details of the maximum levels of radiated and conducted energypermissible within the computer area that will not interfere with the computer operation.
NOTE: Where problems in this area are anticipated or encountered, the equipment supplier shouldbe consulted for recommendations.
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3.4.2 Radiated energy
3.4.2.1 General Unless otherwise specified by the equipment supplier, the radiated levelof electromagnetic energy in the computer room and at other locations of computer equipmentshould not exceed the following peak values:
(a) In the frequency range150 kHz to 470 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 V/m.
(b) In the frequency range470 MHz to 11 GHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.0 V/m.
3.4.2.2 Radiated energy surveyA radiated energy survey may be required during thedesign phase of a computer room or as an analytical tool during remedial investigations. Thesurvey shall comply with the requirements and recommendations of AS/NZS 1052.
For the design phase, the radiated energy survey results should be used to calculate theanticipated level over the operational life of the computer accommodation and provisionsmade. For the investigation phase, excessive radiated energy levels may be rectified by theinstallation of an effective radiated energy shield.
3.4.3 Conducted energy Unless otherwise specified by the supplier, the terminal voltagelimits for the frequency range 0.15 MHz to 30 MHz and the interface power limits for thefrequency range 30 MHz to 300 MHz shall be in accordance with AS/NZS 1044.
3.4.4 Routing and ducting of cables The requirements of this Clause are intended tominimize the induction of power and noise signals onto data communication andtelecommunication cables, which could result in data corruption.
Data communication and telecommunication cables shall be routed in relation to power cables(for computer equipment, lighting, airconditioning or any other purpose) or relatedequipment, to avoid induced interference. The guide for achieving this is set out as follows:
(a) The minimum separation distance between such cables or their related equipment shallbe no less than the distances given in Table 3.1.
TABLE 3.1
SEPARATION BETWEEN POWER ANDDATA CABLES
Circuit ratingUnshielded power
cablesShielded power
cables
kV.A mm mm
≤1>1 ≤2>2 ≤5
>5
300450600
1 500
2550
150300
Where it is necessary for power and data communication cables to cross, they may doso at less than the above required distance provided that the maximum availableseparation is observed and that the cables cross only at right-angles, with straightsections on each side of the crossing point. The minimum straight length shall be thedifference between the appropriate distances listed above and the distance between thetwo cables at cross-over.
(b) Data communication cables shall not be laid in the same duct as power or otherconductors, as specified above, with less than the above separation unless electricallyseparated by a screen which is connected to the safety earth system.NOTE: Routing one group or the other through a metal conduit, earthed as specified, willsatisfy this requirement.
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(c) Data communication cables should not be routed outside a building unless properlyprotected from lightning or similar transient noise signals.
NOTE: See also Clause 3.5.
(d) Fibre-optic cables offer the possibility of avoiding power noise, earthing and lightningproblems.
Further information or cable routing is given in AS 3000 and AS 3080.
3.5 LIGHTNING PROTECTION
3.5.1 General In the presence of electrical storm activity, large electric fields develop inthe atmosphere and in the earth. These fields vary continuously with time at any location inthe storm area and are potentially dangerous to computer equipment within a radius of severalkilometres. The fields and associated lightning discharges may affect computer equipmentthrough the following means:
(a) Direct lightning strike to the building containing the computer equipment.
(b) Mains voltage fluctuations caused by induction into, or lightning strike onto, thecommercial mains network.
(c) High voltage or current induction into, or lightning strike onto, data communicationcables. This is most likely to occur under the following circumstances:
(i) Where a data communication cable directly connects two units of computerequipment which are installed in separate buildings (regardless of whether thecable is routed via an earthed duct or buried underground).
(ii) Where a data communication cable connects two units of computer equipmentinstalled in the same building, but connected to two separate sources of supplyor connected to two separate earth systems. (See also Clause 3.4.4 Items (c) and(d).)
To ensure that the risk of damage to the computer equipment and of danger to operators isminimized, precautions shall be taken as specified in Clauses 3.5.2 to 3.5.4.
NOTE: The protection devices referred to in Clauses 3.5.3 and 3.5.4 are intended to preventequipment damage. Their function may not prevent computer errors.
3.5.2 Building protection The building housing the computer equipment shall beprotected against lightning in accordance with AS 1768.
3.5.3 Electric mains protection Each live conductor entering the area housing computerequipment shall be fitted with a surge diverter (see applicable part of AS 1307) or equivalentdevice.
3.5.4 Data communication cable protection All data communication cables shall beprotected at each end with transient voltage surge protectors when directly connecting twounits of computer equipment installed in either of the following situations:
(a) In separate buildings. (See Clause 3.4.4 Items (c) and (d).)
(b) In the same building, but connected to separate sources of electrical supply. (SeeClause 3.4.4 Items (c) and (d).)
The discharge current shall be routed as directly as possible to a suitable safety earthconnection which is independent of the computer system dedicated safety earth.
The equipment supplier shall nominate a suitable type of protector for each type of data cableat risk.
3.5.5 Equipment protection The computer equipment shall be protected against lightningin accordance with AS 1768.
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APPENDIX A
GUIDELINES FOR FACILITY DESIGN OF COMPUTERINSTALLATIONS
(Informative)
A1 SCOPE This Appendix provides guidelines which apply to installations requiring acomputer room in Environment Types 1 or 2. However, portions of this Appendix may beapplicable to other installations.
A2 GENERAL CONSIDERATIONS Prior to designing a computer facility and in orderto identify whether any external problems exist, carry out a survey of the general area inwhich the installation is to be made. A number of areas where problems may arise are listedbelow, but the list is not exhaustive. Should any problems be found to exist, thenconsideration may have to be given to selecting an alternative location but, where relocationis not practicable, it will be necessary to make special provisions in the design of thecomputer facility so that the particular problem or problems can be obviated. The areas ofconcern are listed below together with appropriate questions, as follows:
(a) Fire and safety Are there any potential fire hazards in the general locality? Whatadditional fire protection will be required?
(b) Security Are there any security problems due to the general locality? Will specialsecurity provisions be required? (See Clause 2.12.)
(c) Abnormal environmental conditionsAre there any abnormal environmental conditions,such as pollution from factories and processing plants? Special room andairconditioning design may be required. (See Clause 2.7.)
(d) Electrical supply What is the type and quality of electrical service available to servethe computer hardware? Is it acceptable? Or do problems exist such as unusual loadingby neighbouring factories or facilities? (See Clause 3.2.)
(e) Excessive vibration Are there heavy presses, rail systems or other types of operationsthat could create excessive vibration within the computer room? Special vibrationisolators may be necessary. (See Clause 2.9.)
(f) Electromagnetic radiation Are there radio, television, radar stations or other sourcesin the area that could create electromagnetic interference? If so, special shielding maybe required or that area should be avoided altogether. (See Clause 3.4.)
(g) Flooding Is there excessive water or flooding in the area? This can be extremelyimportant in ground floor and lower level site locations. It must be considered.
(h) Airconditioning Can the airconditioning facilities be satisfactorily installed?
(j) Tenancy Can the existing facilities be modified to meet the requirements of the user?Problems due to objections from the owner, or other tenants, can occur in tenantedbuildings where computer room facilities are installed.
(k) Telecommunications What is the availability of telecommunication facilities at thelocation?
A3 SELECTING THE COMPUTER ROOM LOCATION (ENVIRONMENTTYPES 1AND 2) The location of the computer room and the other data processing areas may havean influence on the overall efficiency of the data processing operation. Thought should begiven to facilitating the work flow between the actual data processing area and the relatedoffices.
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Selection of the computer site requires evaluation and consideration of several factors. Thefollowing are generally common to all sites:
(a) Location of associated equipmentFor non-distributed systems, the proximity of thecomputer equipment room to the related processing areas, such as data entry anddecollating offices, is important. The work flow must be established and the areasarranged for maximum efficiency. Handling of supplies and paper stock has to beconsidered. Generally, the computer room should be easily accessible to its relatedfunctions.
(b) Interior vs exterior zones of the buildingIt is recommended that the computerequipment room be located in an interior zone (if at all possible). It should be locatedin an area of the building which is least affected by outside temperature or moistureconditions.
If a site is chosen with an outside wall with window glass, it is recommended that theglass area be totally eliminated, i.e. closed in and sealed. If this is not possible, theglass area should be kept to a minimum. In some parts of Australia, double-glazedwindows should be used to prevent condensation in the wintertime.
(c) Floor level The ground floor level is generally considered optimum from thestandpoint of accessibility, if security is not a major consideration and, if there is anoption, this level should be given prime consideration. Floor location, however, is notrestricted to this level. The type of data processing operation and proximity of thecomputer room staff to their base operations often will dictate the floor location.Basement sites may be subject to flooding.
Services to and from the airconditioning plant should be kept as short as possible.
(d) Accessibility Regardless of floor level, the layout should be such as to allow themovement of hardware, air units and other large pieces of equipment into the computerroom. Door openings, corridor widths, floor loadings and lift size and capacity mustbe checked to be sure the equipment can be routed into the computer room withoutabnormal rigging or major building changes.
(e) Security Security is becoming an increasingly important factor in room location.Generally, the interior zone or core area of the building provides for better security.Exterior zones and especially areas with windows are more vulnerable and should beavoided, particularly those on the ground floor.
The perimeter walls around the computer equipment room should extend from thestructural floor to the roof or floor deck above, for security, noise and vapour sealing.Condensers, dry coolers, associated equipment and essential services, such as electricityand water, that are located outside the computer room should be made secure andtamperproof, so as not to be damaged or turned off by unauthorized persons.
A security lock is recommended for in-house security. Magnetic card and othermethods are available, depending on the needs of the user. However, for safety reasons,a door serving as a required exit or forming part of a required exit shall be capable ofbeing readily opened at all times using a single hand action in one operation, notrequiring special knowledge and without recourse to a key, from the side facing anyperson seeking egress.
(f) Floor loading The computer system, when properly arranged for efficient operation,should not overload a floor structure rated at 5 kPa uniform distributed live load.Today’s office buildings are generally designed to this rating or higher.
It is the user’s responsibility to ascertain the adequacy of the floor structure on allexisting buildings and proper floor design ratings for all new buildings. In all cases,the equipment supplier should provide the user with size and weights of the proposedhardware and assist in the general arrangement within the computer room.
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(g) Room expansion The location of the computer room within the building should lenditself to ready expansion. Be sure it is not ‘locked in’ due to the structure of thebuilding, e.g. certain walls cannot be moved, making expansion of the room almostimpossible. Investigate the building construction and determine which walls are load-bearing and which walls are readily movable.
(h) Services Careful consideration should be given to proximity and access to buildingservices, such as electric power, airconditioning, water, drains and other servicesneeded for the facility. It is desirable to be as close to these services as possible, toreduce site construction costs. This may mean locating the computer facility at the rearof the building instead of the front or vice versa.
(i) Vibration Do not locate the computer room above, below or adjacent to areas thatproduce excessive vibration that would affect the computer. (See Clause 2.9.)
(j) Air supply Do not locate the computer room or airconditioning fresh-air intakes nearprocesses that emit contaminating vapours or dust particles detrimental to the computerhardware, e.g. generator set exhaust.
(k) Electromagnetic compatibility Check for possible local electromagneticincompatibility, e.g. emission, susceptibility (see Clause 3.4).
A4 DESIGNING THE COMPUTER ROOM
A4.1 General A block plan showing the computer room and general arrangement of thesupport areas should be developed prior to designing the computer room itself. This plan mayassist in revealing potential design weaknesses, such as access problems, expansionlimitations or an awkward work flow, that should be changed. Exact area dimensions are notrequired to develop the block plan.
After completion of all preliminary work, the room itself should be developed. It isrecommended that the following basic design procedures be followed:
(a) The proposed hardware configuration, arrangement of the hardware, and futureexpansion requirements are key factors that generally establish the room size. There areno fixed rules or easy formulas for making this determination. Each item must bedesigned to the user’s specific needs.
(b) The equipment supplier is responsible for providing the user with adequate siteplanning information. The user is responsible for meeting the installation requirementsof the supplier.
(c) The initial layout may be templates properly arranged on a sheet of 1:50 scale paper,with phantom walls, simply to determine the general floor area required. All hardware,airconditioning units, data safes, service clearances and the like, should be a part of thislayout.
(d) Expansion within the initial computer room is very important and should be includedin the room size. The amount of expansion will depend on the user’s projected growth.
(e) The shape of the room is also important. Long, narrow rooms do not lend themselvesto efficient arrangement of hardware and can create airflow, noise and other problems.
For smaller rooms, the aspect ratio (length divided by width) should not exceed 1.5.
EXAMPLE: Area determined by initial layout . . . . . . . . . . . . . . . . . . . . . . . 70 m2.Anticipated growth factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 %.Total area = (70 m2 × 1.3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 m2.Room size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 m× 10 m.Aspect ratio (10÷ 9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.
Columns, fixtures and other intrusions should also be taken into account when calculating theavailable space.
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A4.2 Acoustic considerations The acoustic properties of the computer room should beconsidered. If treatment is required or desired, the following may be used:
(a) Carpeted floors provide good acoustic treatment owing to their inherent properties.However, carpet should be chosen for its quality and conductive properties. SeeClause 2.1.1 and Appendix B, for further information.
(b) Acoustic wall and ceiling tiles and other absorbers may be used. They should be dust-fibre- and erosion-free, and non-combustible.
(c) If large areas of glass are used on opposite and parallel walls, some treatment willalmost certainly be required, e.g. acoustic drapes. However, large glass areas shouldbe avoided.
(d) Where possible, high noise level equipment should be isolated from the workingenvironment.
(e) Consideration should be given to limiting the ingress or egress of noise to or from theadjoining areas. This may require noise barriers in the floor or ceiling spaces, or both.
(f) External noise emission from plant, such as generators and cooling towers, shouldcomply with local noise regulations.
A4.3 Other considerations When designing computer installations, provision should alsobe made for the following:
(a) Service areas Areas designated for use by engineering personnel may be a part ofevery site. The specific size and requirements will depend on the size of the facilityand whether it is a multisupplier environment.
The equipment supplier’s engineers should be consulted to determine the specific roomsize, electrical outlets required and furnishings, such as desks, tables, workbenches, andstorage cabinets, needed to maintain the computer system properly.
(b) Printer/paper handling room It is recommended that all printers and paper handlersbe isolated from the other computer hardware to minimize the effects of dust and noise.
(c) Equipment location The equipment should be located to enhance the operatingefficiency of the system. Printers should be readily accessible to the bursting anddecollating area. Where practicable, peripheral units should be located adjacent to theirrespective media storage facilities.
Location of the computer hardware relative to airconditioning units and electricaldistribution panels is important and the following points should be considered in thetotal design:
(i) The airconditioner(s) should be located for optimum air distribution. However,consideration should also be given to its location relative to the printer, cardpunch, and other dust-producing units. Short circuiting the dust particles to theair unit filters will reduce contamination of magnetic file devices and magneticfile media.
(ii) The electrical distribution panel should be located within the computer room forsecurity and to minimize the length of power cables to the units.
(d) Furniture Only furniture essential for efficient operation should be located within thecomputer room, to limit the fire loading and static problems. (See Appendix D forguidelines on the control of static electricity.)
(e) Occupancy The occupancy of the computer room should be restricted to essentialpersonnel. Smoking, eating and drinking should not be permitted in the computer room.
Good housekeeping rules should be practised.
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(f) General purpose outlets A sufficient number of general purpose outlets should beallowed for at convenient locations around the room, for use by service personnel andcleaners. The supplier may have specific requirements in this regard.
(g) Media storage in the computer roomThere should be no permanent storage of masterfiles or paper supplies in the computer room. (See also Appendix A.)
(h) Vapour sealing of the computer roomThe computer room walls, floor and ceilingshould contain a vapour seal to prevent transmission of water vapour either into or outof the computer room with the corresponding loss of humidity conditions within theroom.
(i) Thermal insulation Consideration should be given to insulation of the structural floor,walls and ceiling where large temperature differentials exist, e.g. low floortemperatures can cause condensation on the ceiling below.
NOTE: Consideration should be given to the location of the vapour barrier in relation to thethermal insulation to prevent condensation from saturating the insulation and rendering itineffective. Under some circumstances, vapour barriers may be required on both sides of theinsulation.
(j) Infiltration and exfiltration All building elements and joints should be adequatelysealed to prevent the uncontrolled infiltration and exfiltration of air. All penetrationsshould be similarly sealed. Any opening for an exhaust system should be provided withan airtight sealing damper which will be closed when the system is not in operation.
A5 MEDIA STORAGE FACILITY DESIGN
A5.1 Records An initial step in the production of records on magnetic tape, disk, and thelike, is to assess their level of importance. For example:
(a) Vital records Vital records are those which are essential to the continuous operationof the computer system, cannot be quickly reproduced or may be irreplaceable.Examples include important programs, master records, and certain operational data.
(b) Important records Important records are those that while essential or important canwith difficulty or extra expense be reproduced without a critical delay. Mostoperational data have this level of importance.
(c) Useful records Useful records are those which may be readily replaced and their lossdoes not in the meantime present an insurmountable obstacle to prompt restoration ofoperations.
A5.2 Storage consideration After deciding which records must be preserved, the properprotective equipment should be selected and installed. While no universal Standards for thepreservation of records have been defined, the user should review the following:
(a) Risk of fire in the surrounding compartments or structures and its possible effects onthe proposed storage area.
(b) Merits of adding, during site construction, additional fire protection measures in thecomputer room or the storage area, or both.
(c) Existing facilities for storage protection in the building, media storage rooms, fire-resistant cabinets, and the like.
(d) Access control and security available day and night.
(e) Various types of protective storage equipment offered by a number of manufacturers.
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A5.3 Fire-resisting storage Where used, media storage rooms should be of fire-resistingconstruction and provided with automatic smoke detection and fire-extinguishing systems.Both media storage rooms and safes should have a minimum 2 h fire rating. A remotelocation with security and protection comparable to the primary media storage rooms orrecord container should be utilized for storage of duplicate system and application programs.The following points should be taken into consideration:
(a) Media storage rooms where magnetic and paper records are stored should be separatedfrom the computer room and other occupancies by a minimum 2 h rated fire separation(see AS 1530.4). Normal fire-resisting safes and cabinets designed for paper storageallow the temperatures within them to rise to damaging temperatures for magnetic datastorage devices. Specially designed containers should be used for magnetic datastorage. If media storage rooms open into the computer room, a secondary means ofaccess to them should be available for firefighting purposes so that the computer roomis not exposed to the release of heat, smoke and fumes during such operation.
(b) Floor carpeting and drapes may be permitted only if it is demonstrated that theproposed material will not contribute to the spread of fire, does not produce corrosivefumes, is not readily ignited by sparks or burning embers and does not restrict liftingof panels for access to the underfloor space. (See also Clause 2.11.)
(c) Insulation used over piping or duct work and electrical cables should benon-combustible.
(d) Only non-combustible materials should be used to block floor or equipment openings.
(e) With respect to temperature and humidity, the environmental requirements for diskpacks and other media are similar to those for the related units. Media stored atconditions other than operating conditions should be allowed to achieve the conditionsof the operating unit before reliable operation can be expected. This can be achievedby moving the media into the operating environment at least 4 h prior to its use. Whenmedia are stored outside the computer room, the limits for temperature and relativehumidity should be those specified by the media supplier.
It should be kept in mind that rapid changes in temperature can cause condensation. Ifthis occurs, the equipment supplier’s engineers should be notified immediately so thatcorrective action can be taken.
A5.4 Magnetic media storage Equipment suppliers should ensure that operators at theuser’s site are instructed on the proper care of magnetic media. The following informationis furnished as an aid in reducing or preventing magnetic media storage problems:
(a) Magnetic fields Magnetic media should not be allowed to come within the influenceof or contact with magnetic fields at any time. No field strength should be greater than4 kA/m intensity as this may introduce noise or cause loss of information.
NOTE: Field strengths of this magnitude are not normally encountered.
(b) Disk packs It is recommended that disk packs be stored in a dust-free environmentequivalent to the computer room.
(c) Magnetic tapes Reels should always be stored within their containers which in turnshould be stored vertically, e.g. hanging from a rack or stacked side by side.
(d) Flexible disks Diskettes should always be stored within their sleeves and stackedvertically.
(e) Other magnetic media Other types of magnetic media should be stored strictly inaccordance with the manufacturer’s specifications.
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APPENDIX B
GUIDELINES FOR DESIGNING FLOORING FOR COMPUTERINSTALLATIONS
(Informative)
B1 SCOPE This Appendix provides guidelines on the design of floors for computerinstallations.
Two types of floors are covered as follows:
(a) Elevated floors, including recessed subfloors.
(b) Solid floors.
B2 ELEVATED FLOORS
B2.1 General Elevated floors should be designed and tested in accordance with AS 4154.The elevated floor permits routing, protection and concealment of the system cabling and easeof equipment arrangement. The elevated floor also provides an excellent air plenum (somelocal authorities may not permit the use of the elevated floor for an air plenum) and permitsthe addition or relocation of the air grilles when equipment is added or relocated within thecomputer room.
Elevated floors should be constructed to provide protection from static electricity build-up.
B2.2 Construction The design of a raised floor should be such that it retains its integrityand provides adequate thermal insulation in the event of a fire developing in the voidbeneath, until an alarm is raised or sprinklers activate (see Clause 2.6). Where combustiblematerials are used, the raised floor should be faced on the underside with non-combustiblematerial. Materials used to support raised floors built above structural floors should be ofadequate strength, non-combustible and should not incorporate materials having a meltingpoint lower than 350°C.
The top finish of the floor panels must meet the conductivity requirements of Clause 2.1.2.
NOTE: See Paragraph B4 for floor finish.
B2.3 Floor openings The floor opening edges are required to be protected withnon-conductive trim, flush with the floor opening.
The floor air grilles, which may be the adjustable type for air volume and direction control,are required to be flush with the floor panel surface. The air grilles can be constructed ofnon-conductive materials with no metal screws exposed. If the air grilles are constructed froma conductive material, the grilles are required to be insulated from electrical earth. The airflow rating of floor grilles or perforated panels should be based on a pressure differential of25 Pa with the damper fully open, where applicable, and a maximum face velocity of 2 m/s.
Edge cutouts are permissible only in elevated floors that have stringer supports or additionalsupporting pedestals installed. It is recommended that arrangements be made with theinstalling contractor for cutting cable access and air grille cutouts in the floor panels. Cutoutsshould be dressed both top and bottom to remove sharp or jagged edges. One or more panelsshould not be permanently omitted, for air access or the like, since such action may causepanel creep, particularly on stringerless floors.
B2.4 Removal of floor panels It is recommended the floor panels of the elevated floorsystem be readily removable to allow installation of the system cabling and peripheral signalcables. A panel lifting device is to be supplied.
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Care should be taken when removing multiple panels around the perimeter of heavily loadedareas, as this will reduce the stability and strength of the loaded areas. If the underfloor isused as an air plenum it could also cause the environment to become unbalanced.
B2.5 Floor installation The elevated floor should be installed in accordance with themanufacturer’s instructions. Particular attention should be given to the floor levelling. Floorpanels must not tilt or rock.
The elevated floor is required to be completed and thoroughly cleaned prior to the equipmentdelivery date. If the elevated floor is used as an air plenum, the underfloor area is requiredto be vacuumed free of dust, with particular emphasis on the removal of all metal filingsfrom the underfloor area.
B2.6 Ramps Equipment access ramps should be provided to the elevated floor with amaximum slope of 1 in 8. The load characteristics of the ramp should be the same as thoseof the floor panels. Access ramps for the disabled should have a maximum slope inaccordance with AS 1428 or the authority having jurisdiction. Where space is at a premium,consideration should be given to a hoist suitable for the disabled and the movement ofequipment.
B2.7 Bonding of elevated floors The elevated floor construction is required to providea path for the discharge of static electricity through the following means:
(a) The supporting structure is required to be metal and tied to building earth.
(b) The floor panels are required to be constructed in a manner as to provide a continuingpath of electrical discharge. The top surface must be covered by a material whichprovides the required conductivity path to earth.
Any floor surface treatment must preserve the inherent conductive properties of the floorsurface.
B2.8 Temporary protection During installation or other movement of heavy equipment,the elevated floor should be protected from surface damage and concentrated loads. For thispurpose, suitable protective sheeting should be used. Plywood or hardboard with a thicknessof at least 6 mm, or appropriate metal sheeting, is generally suitable.
B2.9 Room maintenance Room cleaning and maintenance is important in keeping aircontamination within safe and acceptable levels. Special attention must be paid to filterchanging, cleaning beneath the elevated floor and the prevention of smoking, eating anddrinking in the computer room. The following warnings should be observed:
WARNINGS:
1 AS MOST RAISED FLOORS ARE NOT WATERTIGHT, WET MOPPING OFTHE FLOOR IS NOT RECOMMENDED. IT MAY RESULT IN A SERIOUSSHOCK HAZARD TO CLEANING PERSONNEL OR IN DETERIORATIONOF THE FLOOR.
2 WAXES AND FLOOR POLISHES SHOULD NOT BE USED BECAUSE OFTHEIR DEGRADING EFFECT ON THE ANITSTATIC PROPERTIES OFTHE FLOOR.
B2.10 Spare floor panels A small number of uncut spare floor panels should be retained.
B2.11 Drainage Provision should be made to allow drainage of the underfloor space incase of accidental flooding, condensation or sprinkler operation. A suitably trapped drain ordrains should be provided at the lowest point or points on the structural floor.
B2.12 Vermin Care should be taken to seal the underfloor space against vermin. As anadditional precaution, the underfloor space should be inspected periodically for signs ofvermin and, if found, steps should be taken to eradicate them and to locate and seal theirmethod of entry.
NOTE: Rats and mice have been known to damage underfloor cabling by chewing the plasticinsulation.
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B3 SOLID FLOORS
B3.1 General A solid floor is a normal structural floor upon which equipment is directlyinstalled.
Small- to medium-sized computer systems may be installed on a solid floor, although anelevated floor is recommended for medium to large size systems.
B3.2 Construction A solid floor shall be capable of withstanding both the distributed andconcentrated loading of the computer equipment plus any ancillary equipment, such as worktables, disk storage cabinets and a fire-resistant safe. In some cases, it may be necessary torestrict equipment layout so that heavier units are installed adjacent to pillars or structuralwalls (see Appendix A, Paragraph A3(f)). However, in so doing, the equipment supplier’sspecifications on minimum access, cable lengths and the like should be adhered to.
If all requirements cannot be satisfied, it may indicate that the room is unsuitable.
The basic floor structure will usually be either concrete or wooden with a suitable finish (seeParagraph B4). It should be noted, however, that a parquetry finish or a normal tongue-and-groove floor without any covering is not desirable. These floors tend to gather dust in thecracks, especially as the planks shrink with age or the parquet tiles come loose, thus makingit very difficult to clean. Such dust may eventually contaminate and damage the equipmentand media.
B3.3 Provision for cables
B3.3.1 General A solid floor may present some difficulties in cabling (both for power anddata) if the computer system comprises more than one unit and if the units are not abutted.There are a number of solutions to the cabling problem, many of which are notrecommended. Paragraph B3.3.2 gives four solutions which are recommended andParagraph B3.3.3 gives two that are not.
B3.3.2 Recommended solutionsThe following are recommended solutions:
(a) Overfloor but under equipmentThis method is only possible if all units in the systemare abutted. Cabling between units is totally concealed beneath the equipment, with twopossible exceptions, i.e. the power cable to the system, and data cables to remoteterminals. Both these problems are solved if any part of the system abuts against awall. If the system is totally freestanding within the room, the power could be suppliedfrom a floor-mounted outlet adjacent to or underneath the equipment. The outlet shouldbe accessible but not placed where it constitutes a mechanical hazard to personnel.
(b) Overfloor but inside ducts This method provides protection both to cables andpersonnel at moderate cost—cables between freestanding units and those between unitsand walls are routed through ducts. Ducts may be supplied in various lengths withaccessories, e.g. mounting hardware, right-angle transitions, by the computer equipmentsupplier, or may be tailor-made by the user to suit his or her particular layout. A ductshould have the following characteristics:
(i) Be mechanically rigid and firmly mounted to the floor or equipment, or both,at both ends.
(ii) Be strong enough to walk on—the top should have a non-slip surface.
(iii) Be readily visible so that personnel are unlikely to trip over it.
(iv) Have a top cover that is removable along its entire length to provide full accessto the cables.
(v) Be constructed of non-combustible material where power cables are installed.
NOTE: Some equipment suppliers may require that power and data cables do not sharethe same duct unless the duct is internally divided by an electrical screen to preventnoise from being induced into the data cables.
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The advantages and disadvantages of over-floor ducts are as follows:
(A) Advantages Tidy, cables out of sight, reasonably easy to clean the floor,moderate cost and no alterations required to the floor.
(B) Disadvantages Trolleys cannot be wheeled over ducts unless a ramp isprovided on either side. Relocating equipment could involve modifying lengthsof ducts or replacing them with new ones.
(c) Within ducts recessed into floorThis method is similar in principle to that describedin Item (b). However, in this case, the duct is recessed into the floor with the top coverflush with the surface. It overcomes some of the problems associated with the above-surface duct, but has problems of its own—including cost of installation. Somecharacteristics required of this type of duct are as follows:
(i) The cover is required to be perfectly flush with the floor surface, with no dust-collection cracks.
(ii) The cover is required to be watertight.
(iii) The cover is required to be removable along its entire length to provide fullaccess to the cables.
(iv) The cover and duct have to be strong enough to bear the weight of personnel,media trolleys and the movement of equipment when necessary.
(v) The cover should be constructed of non-combustible material where powercables are installed.
NOTE: Some equipment suppliers may require that power and data cables do not share thesame duct unless the duct is internally divided by an electrical screen to prevent noise frombeing induced into the data cables.
The advantages and disadvantages of recessed ducts are as follows:
(A) Advantages Very tidy, cables out of sight, very easy to clean the floorand no obstruction to personnel or trolleys.
(B) Disadvantages Could be expensive to install and does not lend itselfreadily to relocating of equipment within the room.
Although this is a recommended solution, the costs should be considered.
(d) Through holes in floor This method involves drilling holes through the floor undereach unit, large enough to accept cables and connectors. The cables are run underneaththe floor, either in cable trays or attached at intervals to the underside of the floor. Theadvantages and disadvantages are as follows:
(i) Advantages Tidy, cables out of sight, easy to clean floor, no obstruction topersonnel or media trolleys and moderately inexpensive.
(ii) Disadvantages Holes may be difficult to drill, holes may weaken the floor,relocating equipment means drilling new holes, holes must be sealed to maintainthe fire rating of the floor and the integrity of the computer environment, andwaterproofed to protect the floor below.
This solution is only recommended if the fire rating of the floor is not diminished anda safe and easy access is available to the underfloor area.
B3.3.3 Solutions not recommendedThe following solutions are not recommended:
(a) Over open floor with no protection Although this method is the simplest and thecheapest, it has the following serious disadvantages:
(i) It is hazardous to personnel.
(ii) It is hazardous to the equipment (should a cable be snagged).
(iii) It is very difficult to clean the floor properly without disturbing the cables.
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(b) Chased into concrete floor and cemented overWhile the result is tidy, this methodis totally inflexible. Once completed, it is extremely difficult to replace cables (shouldit be necessary) or to relocate equipment without contaminating the computerenvironment. Such a project could also be costly and time-consuming.
B4 FLOOR FINISH
B4.1 General The following guidelines apply to the choice of floor finish.
B4.2 High pressure laminate High pressure laminate is used mainly on access floorpanels. It does not require waxing and can be cleaned by damp mopping. It normally providesa dissipation path for static and is the most widely used of all floor coverings. It is stronglyrecommended.
B4.3 Vinyl Conductive vinyl can also be used on elevated floor panels. However, it ismore frequently used as a covering material for solid floors when elevated floors are notused. This type of covering generally requires more maintenance.
B4.4 Carpet Where carpet is desired, it should be of a type with resistance specified bythe manufacturer, or is actually measured, to fall within the range specified in Clause 2.1.2in accordance with the test methods described in Appendix E, without requiring special orregular treatment.
Generally, treating carpet with antistatic solutions is not satisfactory. The carpet should bevacuum-cleaned daily and shampoo-cleaned as required.
NOTE: Low-quality carpets may be a source of dust or lint.
B5 STRUCTURAL TESTING OF ELEVATED FLOORS Elevated floors for computerinstallations should comply with the structural requirements of AS 4154.
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APPENDIX C
GUIDELINES FOR DESIGNING AIRCONDITIONING FORCOMPUTER INSTALLATIONS
(Informative)
C1 SCOPE This Appendix provides guidance on designing airconditioning for computerinstallations for Environment Types 1 and 2. Some parts may also have application to theairconditioned office environment (Type 3).
Nothing in this Appendix is intended to supersede any current Australian Standard or specialsupplier requirement concerning airconditioning. Instead, the information given is intendedas a guide where a number of options are available.
C2 GENERAL Computer equipment requires an airconditioning system designed for year-round operation. Ideally, the computer room temperatures are maintained by an individualairconditioning system responsive to the heat load demands of the data processing equipmentand to the general heat load of the computer room.
The airconditioning system must be reliable and must have the capacity and tamperproofcontrol systems to maintain the computer room within the specified tolerances withoutsubjecting the equipment in the room to variations in temperature and humidity.
The electrical input rating of the airconditioning equipment should be stated for the maximumoperating load on the system, in amperes per phase.
C3 VENTILATION AND INFILTRATION The method and type of construction of thecomputer room has a definite effect on the performance of an airconditioning system and theconsequent environment maintained within the space. This is particularly true whenattempting to maintain the relative humidity of the space within the specified tolerances.
If large volumes of cool air are permitted to infiltrate or are intentionally introduced into thespace, the airconditioning system is required to have a means of adding more moisture to thespace. The performance of a computer system is affected when the humidity falls belowspecifications.
The ventilation requirements are to comply with AS 1668.2 and include any additionalinfiltration allowances that are required. All make-up air introduced into the computer roomis required to be passed through a suitable filter (see Clause 2.7.2.8).
Existing comfort airconditioning systems should be isolated and sealed from the computerroom.
Arrangements should be made to limit the change of air with the space outside the computerarea by use of techniques such as air locks.
NOTE: See also AS 1668.2.
C4 CONTAMINATION Chemical and particulate contamination, in sufficient quantities,can contribute to the degradation of computer systems. Common sources of airbornecontaminants are given in Table C1.
As a general guideline, the maximum chemical concentration are given in Table C2 and themaximum particle concentration given in Table C3. Mechanical ventilation andairconditioning systems should use this data as a basis for design performance. This datashould also be used as an analytical tool for remedial investigation.
In any design, the equipment supplier should be consulted regarding the particular sensitivityof the equipment being installed.
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TABLE C1
TYPICAL SOURCE OF AIRBORNE CONTAMINANTSINDUSTRIAL AND COMMERCIAL PROCESS EMISSIONS
Process Emissions
Ceramics manufacture Hydrogen fluoride
Chemical industry Hydrogen sulfideSulfur dioxide
ChlorineNitrogen oxide
OrganicsInorganics
Acids
Electronic industry Hydrogen fluoride Chlorinatedsolvents
Fertilizer manufacture Hydrogen fluorideAmmonia
Hydrocarbons Organics Dust
Food industry Hydrocarbons Organics
Fossil fuel combustion Hydrogen sulfideSulfurSulfur dioxide
CarbonCarbon monoxide
Nitrogen oxideHydrogenchloride
HydrocarbonsOrganics
Meat processing Sodiumhypochlorite
Chloride ion
Metals manufacturing Hydrogen fluorideChlorine
Hydrogen sulfideSulfur dioxide
CarbonCarbonmonoxide
Inorganic dust
Ore processing Hydrogen sulfideSulfur dioxide
HydrogenchlorideChloride ion
Carbonmonoxide
Inorganic dust
Paint manufacture Carbon Hydrocarbons Dust
Polymer manufacture OrganicsHydrocarbons
CarbonCarbon monoxide
Sulfur dioxide Nitrogenoxide
Pulp/paper industry ChlorineHydrocarbons
Hydrogen sulfideSulfur dioxide
Carbonmonoxide
Dust
Refinery industry Hydrogen sulfideSulfur dioxide
CarbonCarbon dioxide
Hydrocarbons Organics
Rubber manufacture Hydrogen sulfide Sulfur compounds
Sewage treatment Hydrogen sulfideSulfur dioxide
OrganicsHydrocarbons
Ammonia Carbonmonoxide
C5 HUMIDITY CONTROL The relative humidity of the computer area is required tobe maintained between specified limits. Maintaining the relative humidity sometimes requiresmoisture to be added or removed by the airconditioning system.
The airconditioner should incorporate a humidifier located in the bypass air stream formaximum efficiency. Humidifying equipment should be designed for high efficiency andminimum operating costs. Particular attention should be given to the ease and frequency ofmaintenance due to the precipitation of solids from the water supply, especially in areas withwater of high mineral content.
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TABLE C2
MAXIMUM CHEMICAL CONCENTRATIONS
Reactive chemical species Maximum Units
Chlorine 0.001 ppm *
Hydrogen sulfide 0.01 ppm *
Sulfur dioxide 0.05 ppm *
Nitrogen oxides 0.05 ppm *
Hydrocarbons 0.24 µg/m3
Particulate contamination 50 µg/m3 24 h
* Measured by volume at 25°C and 760 mm pressure
TABLE C3
MAXIMUM AIRBORNE PARTICLE CONCENTRATIONS
Particles larger than (micron) Maximum (particles/m 3 of air)
0.5 12 000 000
1.0 3 300 000
2.0 550 000
5.0 60 000
10.0 10 000
25.0 1 000
A controlled method of dehumidification shall be provided. This should basically consist ofcooling, then reheating as necessary, to maintain relative humidity within the specified limits.Where electric heaters are used, low watt-density elements should be fitted to avoid falsetripping of fire detectors.
NOTE: The method of humidification should ensure that minerals contained in the water are notintroduced into the conditioned space as they could affect the performance of magnetic tape unitsand printed circuitry. No chemical additives should be used without reference to the supplier.
C6 TEMPERATURE AND HUMIDITY RECORDING INSTRUMENTS In order toprovide a continuous record of the environmental conditions in the computer room, theinstallation of temperature and humidity recording instrumentation is recommended. Shouldthe airconditioning requirements not be maintained, then this record will contain sufficientinformation to establish the extent and duration of the undesirable conditions and assist indetermining any problems concerning the airconditioning system, or operation of thecomputer equipment.
The record of temperature and humidity provides the following:
(a) Verification of the proper function of the airconditioning system. Efficiency losses dueto a malfunction of some part of the airconditioning system are quickly detected.
(b) Sufficient data to determine if a mandatory drying-out period is required (seeClause 2.7.2.7).
(c) Data to establish whether malfunction of computer equipment was due to the computerroom environment being outside design conditions.
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C7 INTAKES, FILTERS AND DUCTS For intakes, filters and ducts, the followingrequirements are recommended:
(a) Fresh air intakes should be located so as to minimize exposures to external sources offlame, smoke and noxious corrosive fumes.
(b) Filters and frames should consist of non-combustible material.
(c) All supply ducts should be metal with insulation to suit the geographical location.Insulation should be non-combustible.
C8 ALARMS It is recommended that audible and visual high and lowtemperature/humidity alarms be incorporated in the airconditioning system. Operators shouldbe instructed on the correct procedure to bring about an orderly shutdown, if necessary, inthe event of an alarm being activated. The alarm thresholds should be set to provide sufficienttime for the operator to execute an orderly shutdown before the environmental limits arereached.
The equipment supplier should be consulted on unattended operation of the equipment andrequirements for automatic thermal shutdown facilities.
Where an elevated floor is installed, it is also recommended that a moisture alarm be installedto detect condensation or airconditioning leakage. The detector(s) should be located at astrategic point(s) on the structural floor.
Audible alarms should be associated with a conspicuous visual indication in order todistinguish the alarm source.
The airconditioning system should be interlocked with the fire detection system whereinstalled (see Appendix D).
C9 OTHER CONSIDERATIONS Other considerations should be as follows:
(a) Maintenance requirements.
(b) Shutdown procedures for maintenance.
(c) Standby capacity.
(d) Energy consumption.
(e) Plant efficiency.
(f) Required hours of operation.
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APPENDIX D
GUIDELINES FOR THE CONTROL OF STATIC ELECTRICITY
(Informative)
D1 SCOPE This Appendix provides guidance for the control of static electricity in thecomputer area (see AS 1020).
D2 GENERAL The generation of electrostatic charges (static) is a naturally occurringphenomenon brought about by the contact and separation of almost any pair of surfaces.Rubbing is not essential but it will usually increase the magnitude of the static produced.
In practice, static may not be noticed either because too little is formed when surfaces arecontacted and separated, or because the charge so formed is rapidly conducted away by thelow surface or bulk resistance of the materials involved.
Persons may suffer electrostatic shocks on touching conducting surfaces (e.g. metal doorhandles, filing cabinets, computer consoles) after walking over carpeted floors, while similareffects may be experienced after rising from a chair, removing outer garments, and the like.Electrostatic shocks are usually accompanied by a small spark which is normally only ofnuisance value, except in situations where the energy involved is sufficient to interfere withcomputer systems or possibly cause permanent damage to delicate electronic components.Indeed, in many cases, a spark is not required as the electrostatic field alone may besufficient to cause the damage.
When the relative humidity of the environment is greater than 50%, there is generally noelectrostatic problem with most textile materials because the normal moisture content of thetextiles is sufficient to lower their electrical resistance to a satisfactory level. When therelative humidity is reduced, the moisture content of the textile materials also decreases,thereby increasing the electrical resistance of the textile and consequently its electrostaticpropensity.
NOTE: Non-textile materials are not as sensitive to changes in relative humidity in this regard.
Obviously, therefore, maintaining the relative humidity above 50% would reduce the staticproblem in most cases. However, the optimum computer environment often ranges below50% which means that many textile materials will have an electrical resistance above thatspecified in Clause 2.1.1 for computer areas.
In order to minimize electrostatic charge generation, one or both of the following approachesmay be taken:
(a) Ensure that the contacting surfaces have a similar position in the triboelectric series.
(b) Decrease the electrical resistance of one or more of the contacting surfaces.
While materials made antistatic by Item (a) above may well have a low electrostaticpropensity to the generation of charges, they suffer from the disadvantage that chargesproduced by any other activity (e.g. rising from a chair) cannot discharge through thesematerials.
The preferred method of static control is to decrease the electrical resistance between thefurniture surfaces and the floor, and that of the floor itself, to within the specified range andthereby ensure that, irrespective of the method of generation, the electrostatic charge willrapidly dissipate. The manufacturer of textile fibres usually achieves this objective byincluding a suitable conducting agent within the fibres at the point of production. Theresulting antistatic effect is generally permanent. A second possibility is to apply a surfacefinish to the fibres which will act as a conducting layer. However, this method suffers fromthe disadvantage that the surface finish wears off in time and requires re-treatment (which
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may be forgotten!). When re-treating carpets, for example, the spray mist may penetratecomputer cabinets, and contaminate the equipment and storage media. Therefore, only carpetsthat have a permanent resistance meeting the criteria (stated in Clause 2.1.1) arerecommended.
Experience has shown that antistatic flooring of the plastic floor-tile kind is very often,indeed almost universally, degraded by polishing.Computer equipment should be located on the conductive floor in relation to potential sourcesof static (e.g. an access doorway from another room which does not have an antistatic floor),such that the equipment cannot be touched by a person who has been in contact with sucha source without that person taking several steps on the conductive floor.
NOTE: Conductance is the inverse of resistance.
D3 FLOOR RESISTANCE TEST METHODSD3.1 General While Paragraph D2 recommends that both flooring and furniture shouldhave conductive properties, the more important of these is the conductive floor. As personnelare always in contact with the floor while moving about the room, any residual charge on thebody will be dissipated rapidly provided that the resistance of the floor is within the limitsspecified in Clause 2.1.1 and that appropriate footwear is worn.
NOTE: Certain types of footwear may have a high electrical resistance.
Floor resistance can be measured and expressed in two ways, either as a surface or bulkresistance. Where an elevated floor with an earthed metal substructure is used, the bulkresistance is the property to be measured. However, if the final floor surface is laid on aninsulating material (e.g. carpet on a rubber underlay), then the surface resistance is theimportant parameter.D3.2 Test situations There are two different test situations, as follows:(a) Laboratory test of floor materials This is the preferred situation as the test conditions
can be accurately controlled. The results can be examined by prospective users priorto purchasing the materials.
(b) Field test of completed floors in situThis test is applicable where it is desired to testan existing floor constructed of materials with unknown conductive properties. Theresults may not be as accurate as in the laboratory tests.
The following requirements shall apply to both test situations:(i) Resistance shall be measured with a calibrated ohmmeter which shall operate on a
nominal open-circuit d.c. output voltage of 500 V.(ii) The mass of each electrode shall be 2.5±0.1 kg and shall have a dry, flat, circular
contact area of 65±2 mm diameter, which shall comprise a surface of aluminium ortin foil 0.015 mm to 0.025 mm thick, backed by a layer of rubber 6±1 mm thick andmeasuring between 40 and 60 durometer hardness as determined with a Shore Type ADurometer (ASTM D-2240-86).
(iii) The electrical resistance of high pressure laminate (HPL), lino and similar type floorsshall be measured with the specified electrodes and an electrode contact liquid. Theconductive liquid shall have the following parts by mass:(A) Anhydrous polyethylene glycol of molar mass 600 . . . . . . . . . . . . . . . 800.(B) Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200.(C) Wetting agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.(D) Potassium chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.
(iv) Measurements shall be made at five or more locations on the floor or floor materialunder test (hereinafter referred to as the ‘test floor’) and the results averaged. Wherethe bulk resistance of an elevated floor is being measured, the measurements shall bemade on five or more separate panels with the electrode placed at the approximatecentre of each panel. No individual value shall lie outside the resistance range specifiedin Clause 2.1.1.
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(v) The report shall contain the date of the test, the temperature and relative humidity ofthe test environment, the individual resistance results and the location of eachmeasurement and, finally, the average resistance for the test floor.
D3.3 Laboratory testsD3.3.1 Conditioning The test floor shall be clean and conditioned for a minimum of 48 hat 20±2°C and 40±3% relative humidity. A recording instrument of the type referred to inAppendix C should be employed to verify the environmental conditions during theconditioning period and during the tests.D3.3.2 Surface resistance The surface resistance shall be measured between two electrodesplaced 1 m apart between centres at any point on the test floor. In order to ensure that surfaceresistance only is measured, it will be necessary to use a ‘guard’ circuit technique, anexample of which is shown in Figure Dl, or to use an insulating rubber underlay.
NOTES:1 When testing a floor covering, the material should be laid on the test floor and should include
any underlay material(s) normally laid with the floor covering.2 When testing an elevated floor where the size of the panels is such that the two electrodes will
be placed on different panels to obtain the required separation, an additional test is required.An additional electrode(s) requires to be placed evenly across the intervening junction(s)between panels in line with the two test electrodes. The lowest reading thus obtained needs tomeet the requirements of Clause 2.1.1. The purpose of this additional test is to ensure that theresistance at the junctions between panels is not masking an inherently low surface resistanceof the panel itself.
D3.3.3 Bulk resistance The bulk resistance shall be measured between one electrodeplaced on the surface of the test floor or finished floor panel and the other on a clean metalcontact on a metal foil underlay or, in the case of an elevated floor, the floor substructure.D3.4 Field testsD3.4.1 Prerequisites The test floor shall be as clean as practicable. The temperature andrelative humidity should be at their normal values and should have been as stable as possibleduring the preceding 48 h. A recording instrument of the type referred to in Appendix Cshould be employed to record the environmental conditions not only during the test but alsoduring the preceding 48 h.D3.4.2 Surface resistance The surface resistance shall be measured between two electrodesplaced 1 m apart between centres at any points on the floor under test. (SeeParagraph D3.3.2, Note 2.)D3.4.3 Bulk resistance The bulk resistance shall be measured between one electrodeplaced at any point on the surface of the floor and the other connected to a suitable buildingearth.
NOTE: This reading may be inaccurate if the test is carried out near any point of the surface thatis connected to building ground, e.g. via equipment leg or conduit.
D3.5 Interpretation of test results Test results should be reported in tabular form(see Figure D2).It may reasonably be implied that the laboratory test results would be typical of any sampleof the product(s) tested provided that the product(s) continue to be manufactured by the sameprocess(es) and remain at the same standard of quality as the test samples. Therefore, it maybe assumed that, for the purpose of this Standard, any floor materials whose test samplesmeet the requirements of Clause 2.1.1 will also meet these requirements when installed in amanner similar to that of the test floor.Field test results give a reasonable guide to the conductive properties of the total test floorinstallation. The results shall not be implied to be typical of any of the materials that makeup the floor.
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41 AS 2834— 1995
FIGURE D1 SURFACE RESISTANCE TEST CIRCUIT (WITH GUARD CIRCUIT)
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AS 2834— 1995 42
RESULTS OF FLOOR RESISTANCE TESTSCONDUCTED IN ACCORDANCE WITH AS 2834 (APPENDIX D)
Laboratory test
Field test
Test subject description . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Temperature and relative humidity
Conditions at time of tests —Highest temperature and RH during preceding 48 hLowest temperature and RH during preceding 48 h
Temperature°C
Relativehumidity
%
TEST MEASUREMENTS
Test Location or Samplenumber
Bulkresistance
Ω
Surfaceresistance
Ω
Surfaceresistance*
Ω
1.
2.
3.
4.
5.
Highest measurement
Lowest measurement
Average measurement
* Use only where a second measurement is required for elevated floors in accordance withParagraph D3.3.2, Note 2.
Tests conducted by: Date of tests
Organization:
Address:
Signature:
FIGURE D2 TYPICAL FORMAT FOR THE RECORDING OF FLOOR RESISTANCE
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43 AS 2834— 1995
APPENDIX E
GUIDELINES FOR IMPROVING THE QUALITY OFCOMPUTER ELECTRICAL POWER
(Informative)
E1 SCOPE This Appendix provides guidelines for improving the electrical quality ofpower services for computer equipment.
NOTE: Nothing in this Appendix supersedes any requirements of AS 3000 or of the regulatoryauthorities.
E2 POWER QUALITY
E2.1 General This Appendix deals primarily with computer equipment that derives itsoperating power from a 50 Hz alternating current source, such as that made available by anelectricity supply authority. Such equipment is designed to operate reliably within certaintolerances of the power supply. (These tolerances vary somewhat from one supplier toanother and from one generation of equipment to another.) More recent computer technologyhas wider tolerances than that of earlier generations. The requirements of Clause 3.2(computer equipment power requirements) are intended to cover the bulk of equipmentcurrently available. The supplier should provide details of the requirements of each unit ofequipment.
Although electricity supply authorities operate to voltage and frequency criteria specified inAS 2926, they usually do not guarantee that these criteria will be met.
E2.2 Aspects of power quality The following are aspects of the power supply whosevariation from nominal values may be of concern to computer equipment users:
(a) Frequency variations The State electricity grids normally supply power with afundamental frequency well within the requirement of Clause 3.2.4. However, powerderived from other sources (such as small towns not connected to the State grid orprivate standby alternators) may not have the required frequency stability.
(b) Harmonic distortion Any significant distortion of the power sine wave, (i.e.harmonics) is usually generated by other electrical loads in the vicinity. Distortion maybecome a problem with some equipment when it exceeds the requirement ofClause 3.2.4.
(c) Average voltage too high or too lowThe nominal voltage may be consistently outsidethe requirements of Clause 3.2.2 or of the computer supplier, or it may vary slowlywith time in association with increases and decreases of loads on the distributionsystem.
(d) Sags and surgesSags and surges are rapid changes in voltage that persist for periodsranging from 10 ms to 10 s before reverting to the previous steady-state voltage. Theyare usually caused by the switching on or off of local loads, such as airconditioning,lifts, plant and machinery. Sags and surges may become troublesome if they exceed thevoltage disturbance requirements of Clause 3.2.3.
(e) Transient impulses Transient impulses may occur as single ‘spikes’ or as bursts ofelectrical noise. They are rapid impulsive excursions of voltage which can each last forperiods ranging from less than 0.1 microsecond to a millisecond or so, and can rise toseveral multiples of the nominal voltage. Noise bursts may occur sporadically orcontinuously. Most computer equipment can tolerate occasional noise spikes or burstsup to relatively high voltages (usually the briefer the spike, the higher the voltage thatis tolerated). However, in some cases, the amplitude and duration of spikes or burstsmay be sufficient to interfere with the normal operation of computer equipment,
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AS 2834— 1995 44
although it is unlikely to cause any permanent damage except possibly where it is dueto lightning (see Clause 3.5).
Transient impulses (or noise) injected via power conductors can be classified as‘common mode’ or ‘normal mode’. Although the end result is the same, this distinctionis made because the source and solution for each are usually different. The modes areas follows:
(i) Common mode noiseCommon mode noise (CMN) occurs as equal disturbingvoltages relative to a common point (usually earth) appearing simultaneouslyin active and neutral conductors. It can be conducted through the mains froma remote disturbing source but, providing the system is well earthed, it is morelikely to be induced electromagnetically from local sources, such as arc welders,X-ray equipment, switching contacts and radio or radar transmitters.Additionally, lightning activity can induce very high CMN voltages over a widearea.
(ii) Normal mode noise (also called transverse mode noise)Normal mode noise(NMN) is a disturbing voltage which appears between active or neutralconductors. It is conducted through the mains and is caused primarily byelectronic or mechanical switching of other loads, usually in the vicinity.
(f) Blackouts These are complete power outages where the voltage falls to zero forperiods ranging from a few milliseconds to several hours. Most computer equipmentcan store enough energy to ‘ride through’ voltage losses of up to 10 ms (seeClause 3.2.3).
E2.3 Improving power quality Where the quality of power supplied to computerequipment is of concern, action may be taken to improve it. The nature of this action willdepend on the type and severity of the problem. Some possible solutions for each of theaspects, described in Paragraph E2.2, are as follows:
NOTE: The power treatment devices referred to are described more fully in Paragraph E2.4; thecomputer equipment supplier may be able to offer further advice.
(a) Frequency variations The solutions are as follows:
(i) If power is derived from the State grid or a town supply, the supply authorityshould be approached for a solution.
(ii) If a private motor-alternator set is supplying the power, it should be checkedfor—
(A) maintenance;
(B) improper loading; and
(C) level of frequency stability.
(iii) If the source of the problem cannot be rectified, an uninterruptable powersupply (UPS) or a suitable motor-alternator set may be considered.
NOTE: Frequency variations should not be a problem with the State electricity grids.
(b) Harmonic distortion As harmonic distortion is usually generated by loads in thevicinity, often within the same building, installation of a dedicated line in accordancewith Clause 3.2.7 should reduce the level of harmonics in many cases.
(c) Average voltage too high or too lowThe solutions are as follows:
(i) If the average voltage is consistently high or low, the supplier may be able toadjust the equipment to operate on a voltage range that covers the suppliedvoltage. Many computer units have the facility to operate from the major worldvoltages. However, as Australia’s nominal voltage (240 V) is one of the highest,the facility is more likely to benefit situations where the voltage is consistentlylow.
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45 AS 2834— 1995
(ii) If the average voltage is consistently high or low, or if it varies greatlythroughout the day (e.g. is low during weekdays and is high at nights and atweekends due to industrial loading), an approach can be made to the electricalsupply authority. Depending on the particular circumstances, they may be ableto improve the voltage level and its stability.
(iii) If the average voltage is consistently too high or too low, a simple step-up/step-down transformer may suffice. If the voltage varies greatly, a more elaboratepower treatment device may be required.
(d) Sags and surgesThe solutions are as follows:
(i) Where sags and surges are caused by load-switching within the computersystems, it may indicate that the power conductors supplying the computerequipment are not sized in accordance with Clause 3.2.7.
(ii) Where variations are due to the switching of loads within the same building, itmay indicate that the power conductors common to the computer and otherloads are not sized correctly.
(iii) Where caused by load-switching in the vicinity, but outside the buildinghousing the computer, an approach may be made to the electrical supplyauthority. (See Paragraph E2.3(c)(ii).)
(iv) Sags and surges may be eliminated or minimized by the installation of certaintypes of power treatment devices.
(e) Transient impulses Where transient impulses are of concern, there are two basicapproaches as follows:
(i) Locate the source and remove or correct it.
(ii) Filter the power input to the computer equipment.
In extreme cases, most electricity supply authorities have the authority todisconnect devices that cause interference to other consumers, unless suchdevices are altered or adjusted to eliminate the interference. Most computerequipment has built-in filtering in the power supply to enable it to handle areasonable level of conducted electrical noise. Where the noise level is deemedto be beyond the handling capacity of the equipment, the following steps maybe required, the nature of which will depend on whether the noise is commonmode noise (CMN) or normal mode noise (NMN):
(A) Common mode noiseThe solutions are as follows:
(1) Common mode noise is usually induced electromagnetically. Powerconductors should be routed away from the vicinity of knownsources (arc welders, radio transmitters, X-ray equipment and thelike). Shielded power conductors may be used to connect thecomputer equipment, or the power conductors may be routed via ametallic conduit. The screen or conduit should have a low impedanceconnection to building earth.
(2) An isolation transformer or line conditioner will usually eliminatemost cases of CMN. (Some other types of power treatment devicesare also effective, but would not normally be considered only toremove CMN.)
(B) Normal mode noise The solutions are as follows:
(1) Normal mode noise is usually caused by switching. Installing adedicated line with conductors sized as per Clause 3.2.7 willminimize noise originating from loads within the same building.
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AS 2834— 1995 46
(2) A line conditioner will usually eliminate most cases of NMN. (Someother types of power treatment devices are also effective, but wouldnot usually be considered only to remove NMN.)
NOTE: To determine whether noise on a particular power phase is CMNor NMN, a three-phase power line analyzer of the type referred to inClause 3.2.2, Note 3, may be used with its three inputs connected phase-to-neutral, phase-to-earth and neutral to-earth, respectively. CMN will showas simultaneous impulses on the phase-to-earth and neutral-to-earthconnections. NMN will show impulses on the phase-to-neutral connectiononly.
If a line conditioner or certain other types of power treatment devices areto be installed, such measurements need not normally be made as thesedevices will handle both CMN and NMN.
(f) Blackouts Most modern computer equipment can ride through a momentary blackoutof the type that causes lights to flicker. Some power treatment devices can storesufficient energy to maintain an acceptable output for about 10 ms. To cope with longerterm blackouts, there are two basic approaches. Both are relatively expensive, and theircost would have to be weighed against the consequences of an interruption of mainspower or of an extended blackout. The following are ways for providing power duringblackouts:
(i) A standby engine-alternator set will provide power independent of thecommercial mains. However, there would still be an interruption between thecommencement of the blackout and the time required to start the engine-alternator set and to bring it up to speed, plus another brief interruption whenswitching back to mains power at the end of the blackout.
(ii) An uninterruptable power supply (UPS), as the name suggests, will permit thecomputer equipment to continue to operate without interruption in the event ofa blackout. Depending upon the capacity of the UPS system and the computerload, the UPS will keep the equipment operating for a period of time rangingtypically from a few minutes to half an hour. This period may be long enoughto handle a blackout of short duration, to bring the computer system to anorderly shutdown or to bring a standby engine-alternator set into operation.
(iii) A UPS and standby engine-alternator set may be combined to provide long-termuninterruptable power.
NOTE: There are a number of other factors that are relevant when considering either a UPS oran engine-alternator set (see Paragraphs E2.4 and E3).
E2.4 Power treatment devices
E2.4.1 General considerations The following is a brief description of some of the powertreatment devices that may be used to improve the quality of power provided to computerequipment. The list is not intended to be comprehensive. New devices become available fromtime to time. Two or more basic devices are sometimes combined to provide the differentfeatures of the components in a single enhanced device.
When choosing power treatment devices, the following should be taken into account:
(a) The untreated quality of the power available, e.g. noise, sags and surges.
(b) Alternative or additional measures that may be taken, e.g. dedicated line.
(c) The quality or power required, e.g. tolerance of the computer equipment.
(d) The cost of the devices.
(e) The location of the device and its environmental impact with regard to factors such asheat, acoustic noise and radiofrequency interference.
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47 AS 2834— 1995
E2.4.2 Particular devices Particular power treatment devices together with summaries oftheir capabilities are as follows:
(a) Noise isolation transformer This is a transformer with a Faraday screen betweenprimary and secondary windings. Triple-shielded devices can provide up to 140 dBattenuation of CMN and a leakage resistance in excess of 10 GΩ.
The following is a summary:
(i) Very good protection against CMN, including noise generated by lightning.
(ii) Little effect on NMN.
(iii) No maintenance required.
(iv) Low output impedance.
(b) Electronic line conditioner An electronic line conditioner usually consists of anisolation transformer or a transformer with multiple tappings, or both. Electroniccircuitry monitors the output voltage and selects the appropriate tap (triac-switched) toprovide the required output voltage. Regulation depends on the tapping increment andthe response time. It provides up to 120 dB attenuation of CMN. NMN attenuation mayvary from very little to about 60 dB, depending on the frequency components of thenoise and, generally, higher frequencies are better attenuated.
The following is a summary:
(i) Very good regulation (although output may vary in step within the regulationlimits).
(ii) Very good protection against CMN.
(iii) Moderate protection against NMN.
(iv) Some maintenance may be required from time to time.
(v) Low output impedance.
(c) Electric motor-alternator set An electric motor-alternator set (sometimes called a‘buffer set’) consists of a synchronous motor or an induction motor with a 50 Hzalternator mounted on a single shaft (although it can also be used to generate power atother frequencies, such as 60 Hz or 400 Hz, by substituting a suitably-wired alternator).
The output is totally isolated electrically from the input (provided that input and outputwiring are carefully separated). Therefore the output is normally free of sags, surgesand noise. Voltage regulation is typically±5% of nominal for a wide range of inputvoltages (assuming the size of the system is correctly rated). The output frequencyexactly follows the input frequency when the motor is up to speed, although there maybe some slippage when using an induction motor under heavy load. This system canprovide up to 0.5 s ‘ride-through’ in the event of a momentary blackout by virtue ofmechanical inertia.
The following is a summary:
(i) Good voltage regulation.
(ii) Very good immunity to sags, surges and noise (both CMN and NMN).
(iii) Frequency may slip slightly if the motor is an induction type and the system isheavily loaded.
(iv) Can ‘ride’ through momentary blackouts.
(v) Bulky.
(vi) Acoustically noisy.
(vii) Periodic maintenance required.
(viii) Poor power transfer efficiency.
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AS 2834— 1995 48
(d) Uninterruptable power supply (UPS)There are many variations and features, butbasically a UPS consists of three components— rectifier/charger, batteries and inverteror d.c. motor-alternator set as follows:
(i) Incoming power is rectified and filtered to produce a smoothed d.c. voltage.
(ii) The smoothed d.c. voltage charges a bank of rechargeable batteries.
(iii) Current is drawn from the batteries by the inverter (or motor-alternator) whichregenerates the 50 Hz power (or optionally 60 Hz or 400 Hz) with regulatedvoltage.
The output frequency (if 50 Hz) may be locked to the input frequency, and hencesubject to any variations in the input frequency; or it may be very accurately controlledindependently of the mains frequency.
The main feature of a UPS is its ability to continue supplying power to the loadwithout interruption in the event of a blackout. The length of time that the UPS willoperate during a blackout depends on both the capacity of the batteries and the size ofthe load. Because the output of a UPS is derived from a smoothed d.c. voltage source,it is inherently free of any noise (CMN and NMN), or sags and surges on the inputvoltage. The output voltage is regulated.
A UPS may be operated in either continuous mode or in forward transfer mode. Incontinuous mode, the load draws power from the UPS at all times, thus takingadvantage of its power treatment features even when normal mains power is available.In forward transfer mode, the load draws current normally from the mains, andswitches electronically to the UPS only when there is an interruption of the mainspower. A continuous mode UPS requires a greater capacity rectifier section than anequivalent forward transfer mode UPS. A UPS should be used in applications whereany interruption to the power supply would be intolerable.
The following is a summary:
(A) Excellent voltage regulation and immunity from CMN, NMN, sags and surges.
(B) Frequency may be crystal-controlled or locked to the mains frequency.
(C) Can ‘ride’ through blackouts for varying periods (typically 30 min).
(D) Requires regular maintenance.
E2.4.3 General guide As a general guide when selecting a power treatment device, thefollowing characteristics (where applicable) may be considered as minimum requirements:
(a) CMN attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >65 dB.
(b) NMN attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >25 dB.
(c) Voltage regulation at≤ 100% load and for input±10% . . . . . . . . . . . . . . . . ±3%.
(d) Frequency regulation (where controllable) . . . . . . . . . . . . . . . . . . . . . . .±0.5 Hz.
(e) Winding isolation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . <2 pF.
(f) Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Required.
(g) Total voltage harmonic distortion . . . . . . . . . . . . . . . . . <3% (unity power factor).
and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . <5% (any load).
NOTE: The total voltage distortion should be not less than 3% into a resistive load of unitypower factor and not less than 5% under any load condition into an active computer load.
(h) Response time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ms.
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49 AS 2834— 1995
Most commercially available power treatment devices have characteristics (where applicable)which meet or exceed those listed above. In some applications, certain characteristics maynot be required; in other applications, some characteristics may have more criticalrequirements.
E3 STAND-BY OR EMERGENCY POWER Some form of stand-by or emergencypower source may be required in situations where blackouts (other than momentary ones)occur regularly or where the cost resulting from power interruptions would outweigh the costof providing the stand-by or emergency power.
When planning a stand-by power source that will be required to supply emergency power formore than a few minutes, it should be noted that such a source may have to provide powerfor lighting, airconditioning (where applicable) and other ancillary services in addition topowering the computer equipment. The stand-by power source must have sufficient capacitysuch that switching loads and starting currents, e.g. from the airconditioning, not causeunacceptable disturbances on the power input to the computer equipment. To avoid suchdisturbances, a separate stand-by power source may be considered to provide power for theancillary services.
Types of stand-by or emergency power sources are as follows:
(a) Engine-alternator set Consists of an alternator driven by an internal combustionengine, and has a speed control to ensure that power from the alternator is at thecorrect frequency, e.g. 50 Hz. May be started manually or automatically at the onsetof a blackout. Takes up to a few minutes to start and to stabilize at operating speed.Voltage regulation is good provided the alternator is adequately sized. CMN and NMNisolation is total.
The following is a summary:
(i) Delay of up to a few minutes to become operational.
(ii) Totally independent of mains power and mains disturbances.
(iii) Low harmonic distortion.
(iv) Frequency may wander.
(v) Good voltage regulation, if correctly sized.
(vi) Bulky, heavy, polluting and acoustically noisy.
(vii) Requires regular maintenance.
NOTE: See also Paragraph E2.3(f).
(b) Uninterruptable power supply (UPS)See Paragraphs E2.3(f) and E2.4.2(f).
(c) Combination of UPS and motor-alternator setSee Paragraph E2.3(f).
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