htm electrical services supply and distribution.pdf
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DH INFORMATION READER BOX
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Department of Health / Estates and Facilities Division
HTM 06-01, Part A
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HTMs 2007, 2011 and 2014
Oct 2006
PCT CEs, NHS Trust CEs, SHA CEs, Care Trust CEs, Foundation
Trust CEs , PCT PEC Chairs, NHS Trust Board Chairs, Special HA
CEs
Department of Health libraries, House of Commons library,
Strategic Health Authorities, UK Health Departments, Directors of
Estates and Facilities,
Health Technical Memorandum 06-01, Part A, provides guidance
on the design, installation and testing of all fixed wiring and
integral electrical equipment used for electrical services within
healthcare premises.
For Recipient's Use
Health Technical Memorandum 06-01, Part A: 'Electrical services
supply and distribution'
LS2 7UE
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0113 254 5932
Chris Holme
Department of Health/Estates and Facilities DivisionQuarry House, Quarry Hill
Leeds
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Feb 2007
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Electrical servicesHealth Technical Memorandum06-01: Electrical services supply and
distribution
Part A: Design considerations
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Published by TSO (The Stationery Office) and available from:
Onlinewww.tsoshop.co.uk
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Published with the permission of the Estates andFacilities Division of the Department of Health,on behalf of the Controller of Her Majestys Stationery Office.
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HTM 07
Environment &Sustainability
HTM 08
SpecialistServices
HTM 01
Decontamination
HTM 02
MedicaGases
P li i d
INTERNAT
IONAL&
EUROPEANSTA
NDARDS
IND
S
INDU
STRY STANDARD
S
HEALT
H SPEC IF IC DOCUM
ENTS
HEA
LT HTM 00
Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Health Technical Memorandum 03Heating and ventilation systems
Health Technical Memorandum 04Water systems
Health Technical Memorandum 05Fire safety
Health Technical Memorandum 06
Electrical servicesHealth Technical Memorandum 07
Environment and sustainability
Health Technical Memorandum 08Specialist services
Some subject areas may be further developed into topicsshown as -01, -02 etc and further referenced into Parts A,
B etc.Example: Health Technical Memorandum 06-02 Part Awill represent:
Electrical Services Electrical safvoltage systems
In a similar way Health Technicawill simply represent:
Environment and Sustainability
All Health Technical Memorandinitial document Health Technic
which embraces the managemenfrom previous documents and exissues.
Some variation in style and structopic and approach of the differegroups.
DH Estates and Facilities Divisio
the contribution made by profesengineering consultants, healthcNHS staff who have contributed
Figure 2 Engineering guidance
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Health Technical Memorandum 06-01 Electricalservices supply and distribution replaces HealthTechnical Memorandum 2007 Electrical servicessupply and distribution and Health TechnicalMemorandum 2011 Emergency electrical services,and absorbs Health Technical Memorandum 2014 Abatement of electrical interference.
This part (Part A) provides guidance for all works on thefixed wiring and integral electrical equipment used forelectrical services within healthcare premises.
This document should be usedesign work ranging from a nmodifying an existing final sueach section will depend on thworks.
It provides guidance to managon how European and British
electrical safety such as the IEBS 7671, the Building RegulaElectricity at Work Regulationtheir duty of care in relation t
Work etc Act 1974.
Executive summary
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Main working group
Owen Cusack Northumbria Healthcare NHS Trust
Peter Desforges Develop
Alan Gascoine Mayday Hospital
Ian Hawthorn Sandwell General Hospital
Chris Holme Department of Health Estates and FacilitiesJim Mellish Skanska UK PLC
John Murray Bender UK
Nigel Porter Welsh Health Estates
Mike Ralph Great Ormond Street Hospital
Steve Wilson Faber Maunsell AECOM
Subject working groups
Switchgear and Protection Schneider Electric
Containment Systems
Dick Shelly Skanska UK PLC
Andrew Galloway Great Ormond Street Hospital
Isolated Power SuppliesJohn Murray Bender UK
Electromagnetic Compatibility
Alwyn Finney ERA Technology
Acknowledgements
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Contents
PrefaceExecutive summary
AcknowledgementsChapter 1 Scope of Health Technical Memorandum 06-01
Abbreviations and definitionsChapter 2 Introduction
OverviewHow to read this Health Technical Memorandum
Chapter 3 Initial considerations Sources of supplyResilienceEssential/non-essential suppliesPrimary sources of supplySecondary main sources of supply generationTariff negotiations and private generationSupply voltagesDesign of installations for growth and change
Assessment of existing electrical systemsGreenfield siteNew-build on existing siteNew equipment on existing site
Load profileDiversity factorsConsideration for EMC requirements
Roles and responsibilitiesAccess for maintenanceCommissioning procedures
Connection to the DNOConnection to the healthcare site networkSupply from the DNO
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Category 2 Building services safety and securityCategory 3 Building services environmental controlCategory 4 Medical support services
Electrical infrastructureResilienceElectrical infrastructure system selection
Chapter 5 Power quality Power factor correction
Located at the intake pointLocated at sub-main distribution boardsLocated on the electrical equipment
HarmonicsLocated at the intake pointLocated at sub-main distribution boardsLocated on the electrical equipment
Voltage surge protectionChapter 6 Distribution strategy
Design for resilienceSupply connectionsRisk of transformer failuresRisk of generator failuresOther reasons for failure of electricity supply
Distribution system high voltageHV network one radial circuit with one substation onlyHV network one radial circuit with three substations
HV network three radial circuits each with one substationHV ring network ring with four substations
Primary and secondary distribution systemsPrimary supply unified infrastructurePrimary and secondary supply unified and segregated infrastrPrimary and secondary supply unified and dual-unified infraDual primary and dual secondary supply unified and dual-unDual primary and dual HV secondary supply dual-unified in
Dual primary and dual LV secondary supply dual-unified infFinal circuits
Fixed equipmentPower outletsLighting circuits
Chapter 7 Primary power distribution centres
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LV switchroomsLocationConstruction
Access and egressLayoutFire precautionsEnvironmental requirementsEquipment and notices required to be provided
Chapter 8 Secondary power centres and plant Secondary power general arrangements
Photovoltaic power secondary power sourceWind turbine power source
General secondary power plant locationEssential power capacityEssential and emergency power provisionStandby generators
Design criteria
Component partsGenerator configuration
Mobile plug-in generator island operationGenerator(s) in island operationGenerator(s) operating in parallel with PES
LV generators feeding HV ring mainGenerator control
Generating set management
Multi-set operationMains returnComputerised load management of generators
Standards and referencesGenerator enginesBatteries and battery chargingFuel and fuel storageExhaust systems
Environmental considerationsChapter 9 Protection and switchgear
High-voltage switchgearWithdrawable unitsSemi-withdrawable unitsFixed-pattern units
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Generator protectionLow-voltage switchboards
Form 2Form 3Form 4Motor control centre (MCC)Final distribution boards and consumer units
Low-voltage protection devicesSwitch
DisconnectorFuseCircuit breaker
Low-voltage busbar sectionsDiscrimination of protective devices
Discrimination with HBC/HBC fusesDiscrimination with MCB/MCCBDiscrimination with MCB/fuse
Discrimination with RCDsAutomatic load management of switchgear (HV, LV)
Chapter 10 Tertiary power supplies Batteries for uninterruptible power supplies
Battery typeBattery lifeBattery arrangementsBattery autonomy
Batteries for inverter unitsBattery typeBattery lifeBattery arrangementsBattery autonomy
Generator batteriesBattery typeBattery life
Battery autonomyChapter 11 Electromagnetic compatibility
StandardsProcurement requirementsEMC phenomena
Standards and levels
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Medical IT
Protected extra low voltage systemsSeparated extra low voltage systems
Chapter 13 Earthing High-voltage earthing methods
High-voltage network cablesHigh-voltage generator earths
Low-voltage main earthing methodsLow-voltage generator earths
Switchroom earthsEarths for radiographic roomsMedical IT or isolated power supply earths
MicroshockCircuit protective conductorsFunctional earthMonitored earthing systemsLightning protection
Lightning protection system componentsIonised fields
Chapter 14 Containment Trenches, service tunnels and ductsLadder rack tray basketryTrunking conduitsPreformed wiring containment
Layout considerations
Fire precautionsRemodelling and extensionsCircuit segregationAccess for maintenanceSuitable locations
Chapter 15 Cable and busbar types High-voltage distributionLow-voltage distribution
Cable identificationBusbar distribution
Control alarm and communication cablesControl communication and non-fire-alarm cablesInformation technology cablesFire alarm cables
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
IPS communication
ResilienceThe patient environmentIPS low-power circuits
General low-power circuitsSocket-outlets/connection unitsSockets for special locationsSockets for operating theatre suitesSocket for mobile X-ray units
Spark-proof socketsNumber of outlets per final circuit
Fixed equipmentSupplies to external buildingsTemporary suppliesConnections for mobile trailer unitsGeneral lightingTheatre operating lamps
Examination lamps lightingEmergency escape lightingStandby lightingFire alarm, security circuits and critical alarmsBEMS communication and control wiring systems
Chapter 17 Validation and commissioning Validation of specific plant
Generators and CHP plant
Uninterruptible power suppliesIsolated power supplies
Fixed wiring distribution, switchgear and protectionRecords to be keptAs-installed drawingsBuilding logbook
Appendix 1 Maximum interruption times to the primary supply Appendix 2 Sample test record sheets
Appendix 3 Drawing symbols References
Acts and RegulationsBritish, European and International StandardsDepartment of Health publicationsMiscellaneouspublications
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1.1 Health Technical Memorandum 06-01 Electricalservices supply and distribution replaces HealthTechnical Memorandum 2007 Electrical servicessupply and distribution and Health TechnicalMemorandum 2011 Emergency electricalservices, and absorbs Health TechnicalMemorandum 2014 Abatement of electricalinterference.
1.2 This part (Part A) provides guidance for allworks on the fixed wiring and integral electricalequipment used for electrical services withinhealthcare premises. The document should be usedfor all forms of electrical design work ranging froma new greenfield site to modifying an existing finalsubcircuit.
1.3 This document provides guidance to managers ofhealthcare premises on how European and BritishStandards relating to electrical safety such as theIEE Wiring Regulations BS 7671, the BuildingRegulations 2000 and the Electricity at WorkRegulations 1989 can be used to fulfil their duty ofcare in relation to the Health and Safety at Worketc Act 1974.
1.4 The policies and principles of all engineeringservices are described in Health TechnicalMemorandum 00 Policies and principles, whichshould be read in conjunction with this document.
Abb i ti d d fi iti
BSRIA: Building Services ResAssociation
CCM: CIBSE commissioning
CCTV: closed-circuit televisio
CDM: Construction Design aRegulations
CE: European ConformityCENELEC: The European CElectrotechnical Standardizati
CHP: combined heat and pow
CIBSE: Chartered Institute oEngineers
CPC: circuit protective conduCT: current transformer
DB: distribution board
DBU: distribution unit
dc: direct current
DNO: distribution network o
DRUPS: diesel rotary uninter
DTC: diagnostic and treatme
EC: European Community
ECG: electrocardiogram
1 Scope of Health Technical Memora06-01
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
ESD: electrostatic discharge
ETSI: European Telecommunications Standards Institute
EU: European Union
FL: full load
GRP: Glass-reinforced plastic
GSM: global system for mobile communication
HBC: high breaking capacityHBN: Health Building Note
HDU: high dependency unit
HFN: Health Facilities Note
HGN: Health Guidance Note
HRC: high rupturing capacity
HV: high voltage (11 kV)
HVAC: heating ventilation and air-conditioning
ICU: intensive care unit
IDMT: inverse definite minimum time
IEC: International Electrotechnical Commission
IEE: Institute of Electrical EngineeringIGBT: Insulated-gate bipolar transistor
IM&T: information management and technology
IMD: insulation monitoring device
IP: ingress protection (rating)
IPS: isolated power supplies (also known as medical IT)
ISO: International Standards Organisation
ISS: intake substation
IT: impedance terra earthed (derived from an isolatedpower supply)
MCCB: moulded-case circuit br
MD: maximum demand
Medical IT: medical impedance known as IPS
MEIGaN: Medical Electrical InsNotes
MET: main earth terminal
MRI: magnetic resonance imagi
NEAT: NHS Environmental Ass
NHS: National Health Service
OCB: oil circuit breaker
OJEC/OJEU: Official Journal oCommunity/Union
ONAN: oil natural circulation, a
PEC: protective earth conductor
PEI: primary electrical infrastruc
PELV: protected extra LV
PES: public electrical supply
PET: protective earth terminalPF: power factor
PFC: power factor correction
PFI: Private Finance Initiative
PPE: personal protective equipm
PPS: primary power source
PSCC: prospective short-circuit
PV: photovoltaic cell
PVC: polyvinyl chloride
RCBO: residual current breaker
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1 Scope of Health
SPS: secondary power source
TETRA: trans-European trunked radio access
TFL: time fuses links may also be referred to as tlf time-lag fuses
THD: total harmonic distortion
TN-C: combined neutral and earth throughout theelectrical distribution system
TN-C-S: neutral and earth is combined at point ofsupply and separate throughout the electrical installation
TN-S: separate neutral and earth throughout theelectrical system
TP & N: three-phase and neutral
TPS: tertiary power supply
UMTS: universal mobile telecommunications serviceUPS: uninterruptible power supply
VRLA: valve regulated lead acid (battery)
VT: voltage transformer
XLPE: cross-linked polyethylene
Applied part: part of a medical electrical device which innormal use necessarily comes into physical contact withthe patient for the device to perform its function
or
can be brought into contact with the patient
or
needs to be touched by the patient.
Authorised Person (HV): a person appointed to takeresponsibility for the effective management of the safetyguidance given in Health Technical Memorandum 06-03
correct and in a safe manner. T
direct employee of the healthcEssential: any part of the elecfinal circuits that can be autombetween either the primary or
Medical electrical equipmenintended to diagnose, treat or medical supervision which wil
contact with the patient, transpatient, or detect such energy Note: equipment is not covereMemorandum. The MedicineRegulatory Agency (MHRA) which is responsible for ensurworks and is acceptably safe.
Medical IT (IPS): IT electricrequirements for medical instainclude a monitoring device toof IMD connections, insulatiohigh temperature.
Medical location: location indiagnosic treatment (includinpatient under medical supervi
Group 0Medical location wintended to be used.
Group 1 Medical location welectrical supply is not a rislocation is part of a Group
Group 2Medical location welectrical supply can cause
Note: discontinuity means apower supply (seeMEIGaN).
MEIGaN: Medical Electrical Note published by MHRA.
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Point of use: Electrical distribution points where
electrical equipment may be connected. This may be anaccessory or isolator etc.
Protected extra LV: a SELV system that is earthed at onepoint only. Additional protection against direct contact isachieved by barriers and/or enclosures. Alternatively theinsulation will have a withstand test voltage of 500 Vdc for 60 seconds.
Residual risk: a risk that has not been fully mitigated bythe design process.
Segregated distribution: an electrical distribution thatincludes separated primary and secondary circuits not ofequal size or capacity. The secondary circuits are the onlycircuits that are supported by the standby power system.
Separated extra LV: an LV system (normally not
exceeding 50 V ac or 120 V ripple-free dc) derived from asafety source such as an isolating transformer to BS EN61558-1:1998 and BS EN 61558-2.
Single point of failure: a connection point (other than apoint of use) where any upstream single fault will causethe loss of supply to the downstream parts of thedistribution.
Stakeholder: a person (or organ
interest (not necessary pecuniaryquality and provision at healthcastakeholders will normally be an healthcare organisation.
Tertiary power supply: a third sthe primary and secondary supplof an UPS or battery system.
Unified distribution: primary ((essential) circuits combined as ocommon electrical distribution o
Where the secondary power sour100% capacity of the primary poautomatic devices will be requireessential circuits whenever the prnot available.
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Overview
2.1 Health Technical Memoranda 2007, 2011 and2014 have been superseded and combined into onedocument: Health Technical Memorandum 06-01.
2.2 Health Technical Memorandum 06-01 Part Aaddresses design considerations for the electricalservices supply and distribution within anyhealthcare facility. Part B addresses the operationalmanagement and maintenance of the electricalservices supply and distribution within anyhealthcare facility. Both parts provide bestpractice guidance on the design and operationalmanagement of electrical services within healthcarepremises.
2.3 Throughout this document, the following voltagesare used (see BS 7671:2001 for the defined voltagebands):
Extra low voltage 50 V ac or 120 V ripple-free dc
Separated extra lowvoltage (SELV)
50 V ac or 120 V ripple-free dc
Protected extra low
voltage (PELV)
50 V ac or 120 V ripple-free dc
Low voltage 230 V phase to neutral, phase to earthor line-to-line (medical IT)
400 V phase to phase
High voltage 11,000 V phase to phase
from the various distcircuits and point of
Chapter 3provides guidanceconsidered when planning a of the electrical services.Chapter 4explains how the be assessed to minimise the r
the consequential impact to phealthcare premises. The chaconcept of clinical risk in termof a department within the hchapter also considers the busimilar manner. The chapter may be used in the evaluationstrategy.Chapter 5defines the requirelectrical supply.Chapter 6describes the techprovide an appropriate resiliehealthcare facility (or part wiChapter 7 describes the physswitchrooms, their construct
environmental requirements.Chapter 8continues the desthat may be used for alternatpower supplies.Chapter 9provides the detaiequipment that will be found
2 Introduction
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Chapter 13describes the full earth systems to be used.The chapter has a section for HV, LV, and switchroomearths. In addition, the specific requirements forisolated power supplies, earthing radiographic roomsand circuits with high leakage currents are discussed.The method of providing earth monitoring systems toBS 4444:1989 for mobile trailer units is also consideredin the guidance. The chapter concludes with therequirements for lightning protection systems.Chapters 14and15describe the various cable typesand the respective methods of installing them inhealthcare premises.Chapter 16 describes the various final circuits,including uninterruptible power supplies, isolatedpower supplies, fixed equipment temporary suppliesand alarm circuits.
Chapter 17 provides designers and stakeholders withan insight into the validation and commissioning testsrequired before a new installation may be signed offand formally accepted.Appendices andReferencescan be found at the end.
How to read this HealtMemorandum
2.5 This document has been wformat. The design processlikely to follow a similar plconstruction order to that
2.6 It is recommended that dereviewChapter 4 as well asprojects.
2.7 Designers and stakeholderchapter in relation to the nproject.
Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
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3.1 This chapter introduces the design element of thedocument. The intent is to assist designers andstakeholders to develop the design of electricalnetworks for new builds, but equally it appliesto modifications to existing installations. Somesections of this chapter can be addressed prior to orduring the outline design stage, but all sections canbe addressed before the detailed electrical design
stage.
Sources of supply
3.2 All healthcare premises require an electricalconnection to the public electrical supply (PES),which will be provided and operated by thedistribution network operator (DNO). Electrical
supplies to large healthcare premises are mainlyat 11 kV (high voltage), while smaller healthcarepremises may be supplied at 400 V (low voltage).The supply frequency at both voltage levels willbe 50 Hz (see the Electricity Safety, Quality andContinuity Regulations 2002 for further details).
Within this Health Technical Memorandum, theconnection to the PES will be referred to as the
primary source of supply. Any embeddedgenerating plant and/or combined heat and power(CHP) plant can be used as the primary sourceof supply, provided appropriate measures forresilience, maintenance and safety have beenincluded.
b. tertiary source of sup(v) uninterruptible
rotary or silent
(vi) UPS static;
(vii) battery packs.
3.4 Adequate stocks of the f
generators and/or CHPThe fuel for wind turbinphotovoltaic systems (soreadily available at the otherefore these sources oconsidered as essential pbatteries as a power souautonomy dependent on
and battery supplies shoshort-term measure. Thused as the secondary soappropriate measures fomaintenance and safety the embedded sources oit may be less viable to pconnection than it is to
secondary power suppligenerators.
Resilience
3.5 Large healthcare premis
3 Initial considerations
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Essential/non-essential supplies
3.7 When planning for new installations, the optionof segregated non-essential and essential electricalsystems or a unified electrical system (that is,duplex or simplex) should be evaluated.
3.8 The need for more essential supplies increases thedemand on the standby system. Electrical suppliesin the healthcare sector are growing at a rate of
between 3% and 6% year on year. A suitablephilosophy should be agreed with estates staff toreflect this growth before sizing the standby plantand distribution strategy.
3.9 A risk-orientated approach should be adopted,and different categories of the essential and non-essential load identified to assign appropriate
standby provision (historically, it has beencustomary to have a discrete segregated essential/non-essential service combination). For clinicalareas, there should be 100% essential loadprovision. A segregated duplicated essential systemcould be used to overcome the inherent single-faultbreakdown potential. This would also facilitate theoperational opportunity to test and periodically
validate electrical installations.3.10 The provision of two segregated systems, each of
smaller power capacity, should be balanced againsthaving one larger unified power system in termsof economics and reliability in emergencies. Theavailability of the distribution and final subcircuitsfor testing, validation and upgrading of systemsshould also be taken into consideration.
3.11 In systems that employ a segregated duplicatedessential service, thought should given to the spaceneeded for separate feeders, independent risers andstand-alone distribution board (DB) cupboards soas to reinforce the system resilience. This will help
h l l f il ill i
damaging both circuit cab
as much as possible.3.14 In areas where there are m
separate cable trays shouldof duplex essential and non
3.15 Consideration should be gof BS 5588 and fire-protecroutes.
Primary sources of sup
3.16 This section deals with thedistribution and sub-distrielectrical infrastructure (PEpractice configurations forsupplies (seeFigure 1). Th
presented generally in ordeto high. The selection of a will be dependent on the sindividual design in terms supply, type of healthcare fpatient etc. Whichever conshould be based on a risk aappropriate level of resilien
3.17 The configurations presennot be taken as being definrestrictive. They are intendpractice and not intended any design.
Secondary main source generation
3.18 This section deals with secPEI and presents best pracboth HV and LV standby The configurations are preof resilience, from low to h
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Figure 1 Primary electrical infrastructure for healthcare premises
SOURCE OF ELECTRICAL SUPPLY
PRIMARY SOURCEPUBLIC ELECTRICAL SUPPLY
(PES) DISTRIBUTIONNETWORK OPERATOR
(DNO)LV (400 V) HV (11 kV)
OWV
OLTAGENETWORK(S)
HIGH
VOLTAGE
NET
WORK(S)
High Voltage
Substation
Low VoltageDistribution Switch Panel
Low VoltageSub Main (Unified)Distribution Board
Low VoltageSub Main (Segregated)
Distribution Board
Low VoltSub Main (Dua
Distribution
TERTIARY POSUPPLY
UNINTERRUPPOWER SU
ISPOW
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Figure 2 Secondary electrical infrastructures for healthcare premises
SOURCE OF ELECTRICAL SUPPLY
SECONDARY SOURHEALTHCARE PREMISES
INTERNAL ELECTRICAL INFRAST
AlternativeEnergyPlant
OWV
OLTAGE
NETWORK(S)
HIGH
VO
LTAGE
NETWORK(S)
High Voltage
Substation
Low VoltageDistribution Switch Panel
Low VoltageSub Main (Unified)Distribution Board
Low VoltageSub Main (Segregated)
Distribution Board
Low VoltageSub Main (Dual U
Distribution Bo
TERTIARY POW
SUPPLYUNINTERRUPTIPOWER SUPPL
ISOLPOWER
CombinedHeat and
Power (CHP)P
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responsible for the purchase of electrical energy,
they will also be responsible for the negotiations.However, in the more usual case where theelectrical energy is a pass-through cost, or wherethe building services operator is the healthcareorganisation, the healthcare organisation will beresponsible for the above negotiations.
3.20 The opportunities for alternative energy sourcesshould be explored wherever practical. For example,sources such as CHP or wind power will reduce thenet carbon emissions and potentially provide animproved economic solution. Where alternativeenergy sources are used, the resilience of such plantshould be considered. This may be in the form ofN+1 CHP plant or suitable alternative supplyfrom the DNO.
3.21 Healthcare organisations should use the NHSEnvironmental Assessment Tool (NEAT) bothto help find out how their facilities and servicesimpact on the environment and to estimate thelevel of environmental impact taking place (http://www.dh.gov.uk).
3.22 Where the proposed alterations are formodification and/or adaptations to the internalelectrical infrastructure, tariff negotiations may notbe required. Nevertheless, the use of alternativepower sources should still be considered to offsetthe increased electrical demand.
3.23 Guidance on the environmental benefits ofalternative energy sources can be obtained from:
Building Services Research and Information
Association (BSRIA) (http://www.bsria.co.uk);Chartered Institute of Building Services(CIBSE) (http://www.cibse.org);
Combined Heat and Power Association(CHPA) (http://www chpa co uk);
healthcare facility will h
one of the following vol11 kV Large
floor 11 kV/400 V Medi
typica8500
400 V TP & N Gene
healthclinicbuilddecon
230 V SP & N GP anoff-sit
The types of healthcare
are for illustration and voltage tolerances in thissue of the IEE Regulaand the Electricity SafeRegulations 2002.
3.25 Some larger sites may haintake point) with an in(seeChapters 68). In s
voltage will be either 11connection arrangemenresilience of supply.
3.26 Some healthcare sites, phave expanded over a numultiple intake points (same supply voltage). Tshould be consolidated at a common point. Sucprovide economies with
3.27 The DNO may arrange(under a wayleave agreeelectrical equipment, in
l l l l l d d b d
http://www.dh.gov.uk/PolicyAndGuidance/OrganisationPolicy/EstatesAndFacilitiesManagement/SustainableDevelopment/SustainableDevelopmentArticle/fs/en?CONTENT_ID=4119587&chk=r2HHYehttp://www.dh.gov.uk/PolicyAndGuidance/OrganisationPolicy/EstatesAndFacilitiesManagement/SustainableDevelopment/SustainableDevelopmentArticle/fs/en?CONTENT_ID=4119587&chk=r2HHYehttp://www.bsria.co.uk/http://www.cibse.org/http://www.cibse.org/http://www.chpa.co.uk/http://www.chpa.co.uk/http://www.chpa.co.uk/http://www.cibse.org/http://www.bsria.co.uk/http://www.chpa.co.uk/http://www.cibse.org/http://www.bsria.co.uk/http://www.dh.gov.uk/PolicyAndGuidance/OrganisationPolicy/EstatesAndFacilitiesManagement/SustainableDevelopment/SustainableDevelopmentArticle/fs/en?CONTENT_ID=4119587&chk=r2HHYehttp://www.dh.gov.uk/PolicyAndGuidance/OrganisationPolicy/EstatesAndFacilitiesManagement/SustainableDevelopment/SustainableDevelopmentArticle/fs/en?CONTENT_ID=4119587&chk=r2HHYe -
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
cook-chill: the introduction of cook-chill has
meant more meals are cooked electrically andward-based regeneration ovens have beenintroduced;
electronic patient records (EPR) and patiententertainment systems: although these have avery low electrical power requirement, suchsystems require a significant increase incontainment and space.
3.29 Alterations to existing installations, unless plannedand allowed for during the original construction,can be costly, particularly when structural changesare involved.
3.30 Healthcare premises are frequently remodelledwithin the economic life of an electricalinstallation. Designers and stakeholders shouldidentify means of remodelling the electricaldistribution and determine to what extent anyflexibility for remodelling should be incorporatedwith the initial design.
3.31 Each electrical distribution centre should includean element of equipped and unequipped enclosuresfor retrofitting of switches, protective devices and
so on.3.32 The designers should evaluate, by risk assessment,
the degree of remodelling and natural expansionthat will be incorporated into the initialinstallation. The risk assessment should reflect bothclinical and commercial risks.
3.33 This allowance for growth and remodelling should
be incorporated into the adopted distributionstrategy (see Chapter 6).
Assessment of existing electricalsystems
Greenfield site
3.35 Where the proposed workand not part of an existingassessment of existing electlimited to an understandininfrastructure in the area. Thelp in determining the coreinforcements.
New-build on existing site
3.36 Where the proposed workwithin part of an existing cof existing electrical systemextent of any spare capacityconnection point. The conat the site intake or embed
distribution network. Thisdetermine the practicalitieany reinforcements of switdevices and cables.
New equipment on existing s
3.37 Where the proposed workinstallation of new equipm
of sub-distribution and finrequirements and an undedistribution (including findetermine the most appropand any reinforcements of devices and cables.
Load profile
3.38 Designers and stakeholderelectrical profile of the heastage. This will prove invalviability of any secondary asources (for example CHP
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premises such as GP surgeries. The figures do not
take account of any growth. Power densities at thelower end do not necessarily imply any improvedefficiency over power densities at the higher end.However, power densities outside the range maygive cause for further investigation.
Table 1 Typical range of power densities for ahealthcare facility over a five-year period
Power W/m2 GJ/100 m3
General power 925 3.710.3
IM&T power 36 1.22.5
Medical power 515 2.06.2
Lighting
General 915 3.76.2
Special 0.91.5 0.40.6
Task 1.352 0.50.8
Medical 01 00.4
3.40 Figure 3 shows a typical
hospital. The annual prThe actual shape and kVsite and a function of thprovided.
3.41 The various options of penergy required to satisfevaluated. Where the prshort peak maximum derelation to the average dDNO connection will bexpensive, as the cost ofoptimised at the maximcases, the healthcare orgdeveloping some of the site alternative energy sopower. Where alternativthe resilience of such pla
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time of day
kVA
Figure 3 Typical diurnal electrical profiles for a hospital
Figure 4 Typical annual electrical profiles for a hospital
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Electrical services HTM 06-01 Electrical services supply and distribution: Part A Design considerat
Diversity factors
3.42 The electrical diversity factor is the ratio ofinstantaneous power to the total installed power.Diversity factors can be applied to each element ofthe electrical service (for example the lighting loador low-power load) or to a whole department.
Where the healthcare site is large and has multiplesubstations, the diversity factors can be calculated
for each individual substation. It should be clearthat the diversity factor for a particular service (forexample lighting) may differ during the day andyear, while the diversity of, say, the chiller plantmay have a different cycle. Similarly, the diversityvariation for one department (for example
radiography) may be highe
than in the afternoon, whiemergency department maevenings.
3.43 The above variations in actthe true load profile as iden3.383.41above.
3.44 Designers should assess the
for each service and departjudgement of the site-wideThis figure can then be appower and the allowance fothe electrical capacity of thTable 2 shows some typica
Table 2 Typical electrical diversity factors for healthcare premises
Power density(W/m2)
PF Building diversity
Substationdiversity
Connectload diver
AHU fans 1525 0.95 0.70.90 1.00 0.70.9
Building services pump 13 0.95 0.70.90 1.00 0.70.9
Lifts 58 0.95 1.350.23 0.50 0.30.5
Chiller 2535 0.95 0.90.95 1.00 0.90.9General low power 925 0.95 0.490.60 0.70 0.70.8
Information systems 36 0.95 0.80 0.80 1
Medical equipment 616 0.95 0.350.49 0.70 0.50.7
General lighting 915 1.00 0.49 0.63 0.70 0.70.9
Specialist lighting 0.91.5 1.00 0.350.63 0.70 0.50.9
Task lighting 12 1.00 0.450.54 0.60 0.750
Medical lighting 01 1.00 0.420.54 0.60 0.70.9Notes:
Power density: The power density relates to the relevant internal floor area of the healthcare premises.
Power factor (PF): Power factor is assumed to be the corrected power factor at each substation.
Building diversity The building diversity reflects that not all substations within the healthcare premi
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Consideration for EMC requirements
3.45 Electrical installations must be compliant with therequirements of the Electromagnetic CompatibilityRegulations 2005. The regulations describe theelectrical installation as a manufactured item, andtherefore require the installation to be tested forelectromagnetic radiation and absorption.Procurement contracts for electrical equipment
associated with the distribution of the electricalinstallation should stipulate that the equipmentmust be compliant with the ElectromagneticCompatibility Regulations 2005.
Roles and responsibilities
3.46 The Electromagnetic Compatibility Directive(EMCD) and the Electromagnetic Compatibility
Regulations 2005 describe who is responsible formeeting compliance. There are only two partiesinvolved the manufacturer and the operator.In a healthcare building project:
the designer and installer of an integratedheating, ventilation and air-conditioning(HVAC) or power distribution control systemare the manufacturer;
the manager of the healthcare premises and thebuilding services maintenance organisation arethe operators.
It will not always be pos
equipment that is CE-mwith the EMCD. An inCE-marked and non-CESupply of non-CE-markproviding the installer wthe system can be sure tundue interference to thsensitive to the electrom
the equipment will be u3.47 The designer should ob
the installer demonstratpractice has been applieof any concessions grantcompliant with the instawhich may be used with
3.48 Designers and stakeholdequipment which is supmedical environment wto operate successfully inshould not emit excessivstatement assumes that has an approved policy fmedical equipment whi
designers or stakeholderinstallation.
Figure 5 Roles and responsibilities
Building owner/designer
Ensures system legallycomplies with EMClegislation
Requires documproof of complia
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Access for maintenance
3.49 In order to comply with the Construction, Designand Management Regulations (CDM) 1994,designers need to give due account for access andmaintenance at a very early stage of the design,irrespective of the size, complexity and extent of theproposed installation.
3.50 Electrical services should not compromise the
space and access routes for other services suchas mechanical and public health. Maintenancetasks should be carried out with the minimumdisruption to continuity of supply and business.
3.51 The following documents provide additionalinformation:
Health Technical Memorandum 06-01 Part B
Operational management;Health Technical Memorandum 00 Policiesand principles;
Defence Works Functional Standard DMG 08 Access and accommodation for engineeringservices: space requirements for plant access,operation and maintenance;
manufacturers operational and maintenancemanuals.
Commissioning procedures
3.52 Designers should consider how the installationwill be commissioned and how the required testmeasurements will be made. This will include the
inspection of services that may be hidden at thetime of handover. It will also include theimplications of any phased occupation (seeChapter 17for more information).
3.53 The design team should make an application toh k h DNO h l h
3.55 In cases where the new ins
embedded generator plantPV cells), the DNO will nmethods used to clear any energy sources in order thaonto the DNOs network.
3.56 For greenfield sites, it maycoordinate the activities ofoperator and energy supplcan be completed (see para
3.57 The DNO will reserve thenew installation where thecomply with its criteria.
Connection to the healthcare
3.58 Where the new installation
part of the healthcare sitesapplication to connect willcompletion certificate asBS 7671:2001. The healthentitled to conduct a rangethat the installation is safe any fault currents which mbefore reflecting onto the r
healthcare sites network.
3.59 The site engineer should reconnect a new installation does not comply with the Health Technical Memorasafety guidance. The site enthe right not to connect a
the installation compromistrategy of any other part o
3.60 At a very early stage of theprocurement planning), ththe power requirement andrequest for a suitable suppl
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4.1 This chapter deals with the assessment of risk andthe need to ensure that the design of the primaryelectrical infrastructure (PEI) adequately protectsthe end-user, and in particular patients, fromelectrical failures. It promotes multidisciplinarydesign-team and stakeholder involvementthroughout the design process to ensure anappropriate distribution strategy (seeChapter 6),
incorporating resilience, redundancy andduplication as necessary. This should identify anyresidual risks from the design. The identificationof the residual risks will enable the healthcareorganisation to manage their collective ownershipof risk management and hence make appropriatenon-electrical and/or fixed wiring operational andemergency contingency plans in accordance with
DH Emeregency Planning Guidance.
Introduction
4.2 A failure can occur at any point or at any timein any electrical system, regardless of the designstandards employed. The design and installation ofPEI systems inherently allows failure (by operation
of a protective device) to minimise the risk ofdanger and/or risk of injury. This is true of internalPEI systems as well as the wider PES networkdelivered by the DNO. The effects of accidentaldamage and the need for maintenance and trainingshould not be overlooked. It is essential that an
4.5 The design process shoupoints of failure are minappropriate level of resilRisk management carefuto a design strategy withrelationships, where cosbusiness continuity and
4.6 Failures of the PEI systeconsidered as a consequof the incoming DNO smain switchboard etc. Ithat the emergency powor tertiary power supplyfailure of the PEI itself ipoints of failure should during the design procesystem design may be dfailure.
Note
An inappropriate level of resfailure may compromise pati
Ownership and desig
4.7 The duties of the stakehdesign, or assessment aninfrastructure should enpracticable) that all risk
4 Understanding risk and ownership
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power source (SPS) to cover an outage of the
electrical system. The management of such residualrisks may therefore be to reorganise any postponedelective consultations.
Risk profile
4.8 This Health Technical Memorandum divides riskinto two core elements: clinical risk (subdividedinto patient and non-patient areas) and non-clinicalbusiness continuity risks (subdivided into medicalservices and engineering services). Designers andstakeholders should consult with medical andtechnical staff to evaluate the overall risk andthe measures proposed to address the perceivedoutcomes. Most critical within this assessment isthe mobility and degree of healthcare supportprovided to the patient, including medicalprocedures, critical care and continuity oftreatment.
4.10 Small healthcare premises such as GP practices andhealth clinics/centres may have areas that fall intoCategory 1 and possibly Category 2. Communityhospitals may have departments in Categories 1, 2and 3, but unlikely in Category 4 or 5. Large acute
healthcare premises and above may well havedepartments in all categories. There is no rule thatdefinitively places healthcare premises in any onecategory, or defines one category for a particularhealthcare site.
4.11 Each healthcare facility will have a mixture ofcategories (clinical risks and non-clinical businesscontinuity risks) in varying ratios. The assessedhigher clinical or non-clinical and businesscontinuity risk for any particular area willdetermine the adopted electrical infrastructurestrategy for that area. Designers and stakeholdersshould evaluate the economics of providingd ff d b ( Ch 6)
4.13 The consequence of a pow
categorised against some bgroups and patient care plascale from ambulant throuConsequence is also relatedterms of contingency arranpreparedness and business have a financial implicatiooperational consequence o
in terms of the operation ainfrastructure from the pophysical construction and managerial and technical soperate the electrical infras
4.14 The level of consequence obe evaluated as increasing wcategory, for instance, and per category will equally bduration and extent of the
4.15 IEE Guidance Note 7 (alsoaddresses special locationsIEE guide deals with speciand classifies the dependendepartments have on a sus
The guide relates in part toelectrical supplies and theirequirements. These classiftime performance (secondssupply following an interrucontrolled or otherwise.
4.16 Within a GP practice or hbe assessed as acceptable to
failure in a system, given thto be more mobile than paareas, and staff will be ableaffected area in the event oother end of the scale, for
th f
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point of treatment or care. For the purpose of this
guidance, the patient levels described are notintended to be exhaustive, but rather an aid toconsider the issues.
Category 1 Support service circulation
4.19 These areas do not directly relate to the patientenvironment of any group under Chapter 10in IEE Guidance Note 7. The areas includecirculation spaces, waiting areas, offices and non-patient care areas such as laboratories or financedepartments. Consequently, engineering servicesdo not have an immediate effect on the clinicaltreatment or safety of patients (notwithstandingthe requirements of the escape lighting and so onthat may be provided from a local tertiary power
source).
Category 2 Ambulant care anddiagnostics
4.20 These areas do not directly relate to the patientenvironment of any group under Chapter 10 in
IEE Guidance Note 7. The areas may includepatients in consultation (excluding examination)or general out-patient areas. Loss of supply maygive rise to disruption, inconvenience and areduced environmental quality but would notdirectly compromise patient clinical treatmentand safety. The loss of electrical power to otherengineering services (for example ventilation or
medical gases) equally will not cause concern forthe safety of the patient or staff. There may be a
Category 3 Emergediagnostics
4.21 These areas relate to thof group 0 under ChapNote 7. The areas willwards and some maternot generally connecteequipment. However, medical test equipmen
and connected externafor a short or intermittpatient monitors or ultClinical treatment andcompromised by an inpower. However, the inpower should be limitefor other engineering s
support of the clinical medical gases, hot andcommunication etc (nrequirements of the esbe provided from a loc
business continuity risconnected to the SPS fgreater than three hourequirements of the esbe provided from a loc
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Category 4 Patients in special medical
locations
4.22 These areas will relate to the patientenvironment of group 1 under Chapter 10 inIEE Guidance Note 7. The areas may includeLDRP (labour, delivery, recovery, post-partum)areas (maternity), endoscopy rooms, accident
and emergency general/minors, haemodialysisareas, ECG areas, nuclear medicine, radiographydiagnostic, magnetic resonance imaging (MRI),endoscopic examination rooms, urologytreatment areas, or therapy rooms andultrasound. Patients may have electro-medicalequipment, medical monitoring or medical testequipment connected externally to their bodyfor a prolonged period. Clinical treatment andpatient safety may be compromised (but notendangered) by any interruption of electricalsupply. Electrical protective devices shouldinclude an RCD, but may not require an IPScircuit. Supplementary equipotential bondingwill be required in the patient environment. Anyinterruption of the electrical supply to medicalequipment should be limited to within15 seconds. Consideration may be given toproviding an alternative electrical supply (tertiarypower supplies) within 0.5 seconds, subjectto the range of patient treatment. Otherengineering services used in support of clinicaltreatment should be connected to the SPSwithin 15 seconds of any interruption ofthe electrical supply (notwithstanding therequirements of the escape lighting and so onthat may be provided from a local tertiary powersource).
Category 5 Life support or complex
for a prolonged period. C
patient safety may be cominterruption of electrical natural electrical resistancreduced when electro-meparts are placed in the boequipotential bonding (wenvironment) should be psafety. Best practice provi
but not be limited to, IPSprovision of an alternativ(tertiary power supplies) of any interruption of therequired by the medical eengineering services usedof the patient clinical treaconnected to the seconda
within 15 seconds of anyelectrical supply (notwithrequirements of the escapbe provided from a local
4.24 Tertiary power supplies suparagraphs 16.316.19) oequipment, may be consi
limit the interruption of than 0.5 seconds. StandbChapter 8) may be considlimiting the interruption between 0.5 seconds and Category 4 or Category 5at risk from both a generalocal final subcircuit fault
enhanced levels of resilienpatient therapies may be provided by interleaved cor pendant. Such arrangeability to perform maintedisruption.
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where the loss of electrical power could affect
essential diagnosis of a patient or the ability tooperate a clinic. Essential items of building servicesand plant may also necessitate the closure ofdepartments in the event of a power failure wherethese services are not adequately protected by aresilient electrical system.
4.27 Consideration of the categories in Figure 7 shouldestablish a minimum acceptable risk option at the
point of treatment or care. For the purpose of thisguidance, the non-clinical and business continuitydescribed is not intended to be exhaustive, but anaid to consider the issues.
Category 1 Business support services
4.28 The business support areas are departments such
as finance, stores, laundries and workshop areas.In general, an interruption of the electrical supplymay not compromise the treatment or welfare ofpatients. It may be appropriate to provide a single-conversion UPS (see paragraphs 16.316.19) toallow certain systems such as computer applicationsto shut down safely. Electrical load managementsystems may prove useful where the interruption to
the electrical supply (for these areas) is for morethan four hours (seeparagraphs 8.178.19;notwithstanding non-patient safety measures withthe provision of a tertiary power source).
Category 2 Building services safety and security
4.29 The requirements for these facilities are covered byvarious British and European legislative documents,
for example BS 5839-1:2002. Typically, batterypacks or single-conversion UPS systems willsupport such requirements. An interruption of theelectrical supply could compromise the safety andwelfare of patients. These facilities may be included
on the SPS, where the s
loads would only represof the SPS. An understamaintenance and the capacks employed on thes(notwithstanding the relighting etc that may betertiary power source).
Category 3 Building servcontrol
4.30 The building services ensystems will include HVservices, energy centres management systems. Inthe electrical supply couto the treatment or welf
conversion UPS should certain systems such as cbe shut down safely. Elesystems should be consiinterruption to the electwater systems) gives an internal space temperatu(seeparagraphs 8.178.
requirements of the escaprovided from a local te
Category 4 Medical supp
4.31 The medical support areas disinfection units, laband physiotherapy. An isupply may represent a treatment or welfare of pconversion UPS (seepashould be provided to alcomputer applications t
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Electrical load management systems may prove
useful where the interruption to the electricalsupply (for these areas) is for long periods, saymore than two hours (seeparagraphs 8.178.20;notwithstanding the requirements of the escapelighting etc that may be provided from a localtertiary power source).
Electrical infrastructure
4.32 This Health Technical Memorandum divideselectrical infrastructure into two core sections:primary and secondary (see Chapter 6):
the two types of distribution may share thesame cables, which defines a unified electricalinfrastructure;
where there are two sets of cables common tothe primary and secondary distribution, thenetwork is said to be a dual-unified distribution;
where the primary and secondary distributionhas entirely separate cables, the distributionstrategy is said to be a segregated distribution.
The most resilient distribution strategy will haveboth dual-unified distribution and primary and
secondary power sources.4.33 Business continuity risk assessments evaluated by
cause-and-effect models may be used to analysethe impact of electrical failures on departmentswhich are reliant on the services provided. Withinthe integrated departmental model, considerationshould be given to the cause and effect of electrical
failures which escalate exponentially with time.
4.34 Cause-and-effect risk mod
the global electrical infrastpoint-of-use equipment. Tconsider single electrical famultiple electrical faults ansimultaneous multiple fauland 9).
4.35 A distribution strategy shodrives the risk of failure of
the point of use) to a low oA lower distribution strateredundancy of primary ansupply plant which still alevel indicated above shoconsideration may be givenhigher risk factor than the for a particular clinical area
Resilience
4.36 Overall, the PEI can be cosections:
supply;
distribution;
point of use.4.37 The essential elements of a
are:
redundancy;
moving the first singleto the point of use as p
Figure 8 Electrical failure risks evaluation to clinical categories
RISK OF ELECTRICAL FAILURE BY INFRASTRUCTURE
Distribution strategy (refer to Chapter 6)
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appropriate access for practical maintenance and
testing procedures.4.38 The resilience required to maintain essential supply
in the event of not only primary failures but alsosecondary failures should be considered. A suitableassessment of the likelihood of concurrent failuresoccurring within a foreseeable period should bemade, and therefore the operation and inter-relationship of the system and its component parts
should be fully understood. With regard to theconsequence and risk, any reasonably foreseeablesecondary failures should be appropriatelyprotected against. An example here may be astandby generator failing to start (second-line fault)on a supply blackout (first-line fault).
4.39 Incoming electrical supplies may be constrained by
what the DNO is able to provide, or what has beenassessed as cost-effective for the type of healthcarefacility. The distribution strategy should maintainthe minimum acceptable resilience level throughoutthe internal electrical system.
4.40 An iterative design process will help stakeholders toassess the distribution strategy. The process may beused to determine the location of the first single
point of failure in addition to the method used tomitigate the risks on the distribution downstreamof that point. The provision of tertiary supplies(UPS) on final distribution boards or the ability tomanually reconfigure the distribution may besuitable risk mitigation.
4.41 The effects of electrical power failures due tofaults at any level within the infrastructure can bedesigned out by the robustness of the network
resilience. The distribut
adequate resilience and testing and maintenancewithout placing patientsunnecessary risk. Such sredundancy in certain eexample generators, UPof resilience for maintenpractice.
Electrical infrastructu
4.42 A number of different eform the primary and sesystem (seeFigure 9). Sobe optional dependent oChapter 6) and requiredassessed risk from powerconfigurations of the eleelements will have risk-massociated with the possoccurring. Similarly, eacelements, and the links them will present additioverall risk of a power famitigated by the correctconfigurations and intersystem and component appropriate infrastructucategorised in terms of tresidual risks. Evaluatinmake selection of the apapparent at the point ofinfrastructure.
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Figure 9 Electrical infrastructure generic flow diagram
SOURCE OF ELECTRICAL SUPPLY
PRIMARY SOURCEPUBLIC ELECTRICAL SUPPLY
(PES) DISTRIBUTIONNETWORK OPERATOR (DNO)
LV (400 V) HV (11 kV)
LOWV
OLTA
GENETWORK(S)
HIGH
VOLTAGE
N
ETWORK(S)
High Voltage
Substation
Low VoltageDistribution Switch Panel
Low VoltageSub Main (Unified) Distribution
Board
Low VoltageSub Main (Segregated)
Distribution Board
Low VoltaSub Main (Dual
Distribution B
TERTIARY POSUPPLY
UNINTERRUPT
POWER SUP
ISOPOW
SECONDARY SOUHEALTHCARE PREMI
INTERNAL ELECTRICAL INFRA
AlternativeEnergy
Plant
CombinedHeat and
Power (CHP)
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5.1 The quality of the electrical supply is theresponsibility of the DNO, which will comply withthe requirements of the Electrical Safety, Qualityand Continuity Regulations. However, the use ofthe electrical energy within healthcare premises canaffect the quality of the internal distribution interms of power factor and harmonics.
5.2 Healthcare premises have numerous switch modepower supplies and inherently high inductiveelectrical loads and unless corrected, the powerfactor will be poor, requiring large transformers,cables and high-energy cost. Improving a typicalpoor power factor from say 0.75 lagging to anappropriate power factor of say 0.95 lagging willreduce the kVA demand by 20% and will bereflected as a utility cost savings. The actual
inductive load will vary throughout the day andyear. The inductive load will also vary across thesite according to the location of mechanical plant,lifts and to some extent the clinical departments.
5.3 The normal supply frequency is 50 Hz with atolerance of 1%. The nature of the electricalequipment used throughout the site can inject
secondary frequencies that cause significantdisturbances to the internal distribution and thesupply. The majority of secondary frequencies,known as harmonics, are generated from switch-mode power supplies found in a wide range ofelectrical and electronic equipment
electrical system will be correction equipment shdisconnected if the primand if used in conjunctigenerator plant (or CHPthe generator (or CHP precommendations. Whecorrection equipment is
appropriate cable sizes fshould be used.
Located at sub-main distri
5.6 Power factor correction main distribution boardoutgoing circuits will beof power factor correctio
main distribution boardloads can be corrected wwill save on the capital c
Where the power factorlocated at the intake andboards, the appropriate higher currents should bof the sub-main distribu
equipment may need ov
Located on the electrical e
5.7 Where individual pieceshigh inductive reactance
5 Power quality
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freestanding unit. Where a cubicle of the
switchboard is used to house the power factorcorrection equipment, consideration should begiven to the effect this will have on future flexibilityand remodelling of the power factor correctionequipment and/or the switchboard circuits.
5.10 Power factor correction equipment requires naturalventilation to remove the small amount of heat itgenerates. Further information on the amount of
natural ventilation should be available from themanufacturer.
Harmonics
5.11 The normal supply frequency is 50 Hz with atolerance of 1%. The nature of the electricalequipment used throughout the site can create
secondary frequencies that cause significantdisturbances to the internal distribution and thesupply. The majority of the secondary frequencies,known as harmonics, are generated from shortsurge currents and transient currents arising fromnon-linear electrical loads such as switch-modepower supplies and rotating machinery, variablespeed drives and so on found in a wide range of
electrical and electronic equipment.5.12 Surge transient currents are also caused by lightning
strikes. Further details on the lightning strikes andsurge arrestors can be found in paragraphs 13.3913.49.
5.13 Even-order harmonic frequencies are self-negatingand do not cause a real disturbance to the electrical
distribution. Odd-order harmonics with zerorotation effect, known as Triplen harmonicfrequencies (3rd-, 9th- and 15th-order), and odd-order harmonics (5th, 7th and 11th) can causesignificant disturbances leading to high currentsand voltages, and overheating of cables and
which then should be sized
heat. Consideration shouldof clean-earth conductors fitems such as IM&T comprooms. A single-phase thirbalanced three-phase circuat 70% of the fundamentathe neutral conductor. If threach the distribution tran
reflected into the primary circulate. The unchecked hprimary winding of a distrbe dissipated as unwanted
5.15 The network analysis of hapropagated within the elecmade and communicated tstandby generator. The gen
to reflect the anticipated hHarmonic currents not allgenerator design may caustorque loads and consequegenerator while running. Ofilters or isolating passive hused while the generator is5.18).
5.16 The electrical load of a typwith many modern medicaservices may have non-lineharmonic disturbances) at Unless the harmonics are cdownstream from the tranwinding, the transformer mby the factor-K method which may typically be 70nameplate kVA rating to adamage.
5.17 Alternative methods may it l d t i
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located here, as large harmonic currents may
require neutrals oversized by as much as 300%.5.19 Note for the purpose of this section of the
guidelines, the intake point means the HV/LVsubstation, LV switchboard. Alternatively, wherethe site has an internal HV network, the intakepoint means each such substation LV distributionboard.
Located at sub-main distribution boards
5.20 Harmonic filters may be installed at the sub-maindistribution board, in which case only the outgoingcircuits will be corrected. The advantage ofharmonic filters installed at sub-main distributionboards is that several sources of harmonic inductiveloads can be corrected with one common unit. Thiswill minimise the harmonic disturbance reflectedon the sub-main and main distribution cables andsave on the capital cost and space required.
Located on the electrical e
5.21 Where an individual piea high transient current mode power supply, it isharmonic filters direct tarrangement has the advharmonic disturbances ocables.
Voltage surge protec5.22 Consideration should b
of voltage surge protectiwhere equipment whichvoltage surges is connecinstallation from the int
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6.1 For the purpose of this Health TechnicalMemorandum, it is assumed that the highestdistributed voltage in any healthcare facility will be11 kV. DNO connections to healthcare facilitiesmay be at elevated voltages such as 33 kV, but it isconsidered that such voltages are not distributedwithin the healthcare site. Where healthcarefacilities do have a DNO connection at voltages
above 11 kV, the strategy for such connections(and if appropriate, distribution) should follow thedistribution philosophy described in this chapter.This Health Technical Memorandum onlyconsiders any electrical energy used at low voltageas a three-phase or single-phase connection. ThisHealth Technical Memorandum does recognise thatsome electrical energy used in healthcare premises
will be at SELV or PELV, but is only concernedwith the fixed wiring at low voltage. In a similarway, electrical energy used at high voltage, for somelarge vapour compression chillers for example, isacknowledged, but again this Health TechnicalMemorandum only addresses the fixed wiring atHV.
6.2 When designing the strategy for the electrical
network(s), it is essential to take a holisticapproach. The electrical system may includeHV and LV distribution networks, or just LVdistribution networks, depending on the size of thesite.
switchboards. While this cresilience provided by genedescribe the starting or concan be found inChapter 8
6.5 The resilience can be enhadistribution board with thsupplies such as UPS (seep
Alternatively, the resilience
battery packs fitted to medintravenous (IV) pumps. Falternative supplies can be This section deals with thethe fixed wiring network toresilience.
6.6 To achieve this resilience, a
designers should contributdebate (seeChapter 4).
6.7 The available electrical supverified with the DNO. Mbetween 500 kVA and 800(0.4 kV) connection. Supp750 kVA and 12 MVA shovoltage (11 kV). Where a h
assumed maximum deman12 MVA, the DNO conneor above. Clearly, where than AMD no more than 50electrical infrastructure wil
h AMD ll
6 Distribution strategy
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calculating the resilience of a system it is important
to consider elements that are mutually inclusiveand not mutually exclusive. For example, thestandby generator complement (with a commonpoint of coupling) would be a mutually inclusivesystem. The standby generator complement andprimary electrical infrastructure at a common pointof coupling are mutually exclusive. Best-practiceelectrical distribution strategy solutions provide
resilience to the first-fault conditions at a commonpoint of coupling. Distribution strategies thatprovide resilience above the first-fault condition(at a common point of coupling) are unlikely tobe economically viable. Distribution strategies thatprovide N+1 resilience at several different points ofcommon coupling are more robust andeconomically viable.
Supply connections
6.9 In electrical supplies to large healthcare premises(in electrical terms this means greater than2 MVA), a general arrangement with a dual-PESconnection should be adopted, arranged with eitheran auto-changeover or a manual-selection switch.Dual supplies with diverse routes may be
considered an economic strategy to maximise theresilience and minimise the actual single point offailure. They should originate, if possible, fromseparate DNO substations, ideally fed fromseparate parts of the National Grid, withindependent cable routes to the healthcare sitessubstations. However, the origin and nature of thePES supply routes will largely be beyond the
control of the designer or stakeholders.6.10 Two separate HV supply feeders (or LV if
appropriate) may provide an additional safeguard(for the healthcare site) against a PES connectionfailure. Whether this is practicable largely depends
99.999% (or 0.001% u
mean 5.25 minutes unaHowever, the issue is thfaulty transformer, whicDistribution strategies twith a common primarysecondary linked by a nwould provide a transfoN+1. While both transf
would share the instantaOpportunities for transfmaintenance are improvcontinuity of supply foloutage. Such arrangemeintake substation (ISS) iconnected in parallel orno load are not recomm
Risk of generator failures
6.12 Generators have many mlubrication, cooling andgenerator controls are elelectromechanical devicoutput in response to thgenerators should be ma
readiness state in order tfunction of standby supmay be of the order of 9unreliable), which equaunavailability per year. Tfailures are a result of thoccur during the first fiv
6.13 Distribution strategies tgenerators (each rated apoint of coupling with twould provide generatoThree standby generatorated at 50% of the con
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the guidance within this Health Technical
Memorandum (Parts A and B) and the guidancegiven in Health Technical Memorandum 06-02 Electrical safety systems:
cable faults within the private network;
inappropriate grading of protection devices;
poorly designed network with common pointsof failure;
reliance on one form of standby protection;
accidental isolation.
Distribution system high voltage
6.15 Healthcare premises with an AMD greater than800 kVA will require an internal HV network.There are two basic forms, radial networks (forAMDs up to say 3.5 MVA) and ring networks (forAMDs above 3.5 MVA).
6.16 The following simplified schematics are provided toshow the main HV supply arrangements. They arearranged generally in order of resilience from low tohigh, but their selection as a design solution will bedependent on the supply arrangement available
from the DNO, the type of healthcare facility, andthe level of assessed risk with regard to end-users.Where typical HV distribution arrangements areshown connected to the LV distribution, these areincluded only to assist in the understanding of theLV arrangements. LV distribution arrangements areconsidered more fully inparagraphs 6.316.59.This section does not describe the control of any
standby generator system (seeChapter 8 fordetails).
HV network one radial circuit with onesubstation only
6.17 A single HV supply from t
the healthcare sites HV-swsubstation. This would typ1500 kVA.
6.18 This type of distribution sta small to medium-sized aconly a primary source of sua single point of failure righdistribution switchboard(s
stakeholders should considby the additional resiliencedependent on the clinical r
6.19 The resilience of the HV sbe enhanced by including supply at the intake, as a seor an LV standby generatoClearly, generators at the Ladd resilience to the internmultiple LV standby generprovide any economic ben
HV network one radial circsubstations
6.20 InFigure 11, a single HV
feeds onto the healthcare spart of the substation. Froa single HV radial circuit cHV substations. Each of thtypically be up to say 1500AMD for the healthcare si800 kVA and 3.5 MVA.
6.21 This type of distribution st
appropriate for a healthcardetached buildings. The arsubstation do not exceed aof Category 2. As there is oof supply, this system creat
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generators could be local to each substation or in acommon central facility, depending on the spreadof the site. Clearly, the generator at LV switchpanelswould add resilience to the internal distribution.Having multiple LV generators at a commoncentral facility may provide economic benefit to thehealthcare facility during maintenance periods.
HV network three radial substation
6.23 In Figure 12, a single Hfeeds onto the healthcarpart of the substation. Fthree HV radial circuitsare connected. Each of t
typically be up to 1500 for the healthcare site w
Substation 3Substation 2Substation 1
The healthcare site
DNO connection
Figure 11 HV network one radial circuit, three substations
Substation ISS
DNO or site connection
Figure 12 HV network three radial circuits each with one substation
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and 3.5 MVA. This distribution network is
an enhancement of that inFigure 11above, asfailure of any part of the internal HV electricalinfrastructure will affect a smaller area. The dual100%-rated transformers (not operated in parallel)of substation 2 will provide improved transformerand switchgear maintenance opportunities for thatarea.
6.24 This type of distribution strategy may be
appropriate for a healthcare premises with manydetached buildings. The areas served by any onesubstation do not exceed a clinical risk assessmentof Category 3. As there is only a primary sourceof supply, this system creates a single point offailure right through to the LV distributionswitchboard(s).
6.25 The resilience of the HV supply ofFigure 12maybe enhanced by including a secondary source ofsupply at the intake as a second DNO connection.Standby LV generator(s) connected at the LVswitchpanels will enhance the infrastructureresilience and facilitate improved transformermaintenance opportunities. Standby generatorscould be local to each substation or in a commoncentral facility, depending on the spread of the site.Clearly, the standby generator at LV switchpanelswould add resilience to the internal distribution.Having multiple LV generators at a commoncentral facility may provide economic benefit to thehealthcare facility during maintenance periods.
HV ring network ring with four substations
6.26 InFigure 13, a single HV supply from the DNOfeeds onto the healthcare sites HV-switchboardpart of the substation. From the intake substationone HV ring-circuit connects to all other internalHV substations (which may be more than the fourshown here) Each of the substations would
intake substation should co
and all field substations shswitch type. SeeChapter 9HV protection and switch
6.28 This type of distribution stappropriate for a large acutother support facilities on served by the ISS substatioinclude clinical risk assessm
Category 5. The areas servsubstation 4 may include cof Category 3. As there is oof supply, this system creatfailure right through to theswitchboard(s).
6.29 The resilience of the HV sbe enhanced by including supply at the intake, as a se
Additional transformers at100% rated and not connestandby LV generator(s) coat the LV switchpanels, mainfrastructure resilience. Tsubstation may provide restransformer failure and/or generators could be local tcommon central facility, dof the site. Clearly, the genwould add resilience to theHaving multiple LV standcommon central facility mbenefit to the healthcare famaintenance periods.
6.30 The resilience of the HV renhanced if the ring normring control. Electrical fauto a discrete section of the
b t ti l b t t
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BS 7671:2001. Within special areas, medicalrisk Categories 4 and 5 and wet areas such aspost-mortem rooms, the wiring system would
6.33 The method of fire protfor essential distributionopportunities for flexibl
Figure 13 HV ring network ring with four substations
Substation ISS
SubstatSubstation 3Substation 2
The healthcare site
PES
DNO connection
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Primary supply unified infrastructure
Figure 14 Primary supply unified distributionsystem
6.35 This is the simplest form of LV infrastructure witha primary supply only, direct either from the DNOor from a single HV transformer arrangement,feeding a unified LV distribution network. The
transformer switchgear and main cables should berated to take the AMD and an allowance forgrowth (seeparagraphs 3.283.33).
6.36 The first single point of failure will be theconnection point (to the DNO healthcare sitestransformer). A LV infrastructure of this kind isappropriate for clinical risk Categories 1 or 2 (seeparagraphs 4.124.24). This infrastructure does
not provide for inconvenience-free maintenanceopportunities. Therefore, the infrastructure lendsitself to healthcare premises that do not operate24 hours a day/7 days a week (24/7) facilities, andhence give rise to operational windows in business
6.39 This simple arrangement m
for GP practices, health ceaccommodation, dependenof risk posed by a failure.
Primary and secondary supplsegregated infrastructure
6.40 This form of LV infrastrucsupply, connected directly
or the healthcare sites trandistributed secondary suppinternal LV switchboard. Tswitchgear and main cabletake the AMD and an alloparagraphs 3.283.33). Hogenerator is rated only for part of the healthcare sites
6.41 The first single point of faiconnection point (to the Dtransformer) for the unifieHowever, the segregated essingle point of failure mucuse. This infrastructure doinconvenience-free mainteall areas. Therefore, the inf
healthcare premises that haand part non-24/7 facilitieinfrastructure resilience anstandby generator units toimprove the maintenance obusiness continuity. Alternmanagement system couplinterconnect the essential a
(via cables or a manual bussimilar increased resilience
6.42 An assessment of the potenremodelling the healthcaremade to understand how t
Substation ISS
Risk
category 1
Risk
category 1
Risk
category 2
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6.44 The first single point of failure will be at the main
LV switchboard for the unified circuits, and at thepoint of use for the dual-unified circuits. A LVinfrastructure of this kind is appropriate for clinicalrisk categories 2, 3 or 4, where the dual-unifiedcircuits are used in Category 3 or 4 risk areas (seeparagraphs 4.124.24). This infrastructure may
provide for inconvenien
opportunities in the CaHowever, the same oppthe Category 1 and Catthe infrastructure resiliestandby generator subjeThere is no resilience wi
Substation ISS
Risk category 3 or 4
Riskcategory 2
Riskcategory 1
G
Figure 15 Primary and secondary supply unified and segregated infrastructure
G
From healthcare sites networkor DNO connection
Figure 16 Primary and secondary supply unified and dual-unified infrastructur
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and/or switchgear for the Category 1 and Category
2 risk areas. The unified circuit infrastructure lendsitself to that part of the healthcare premises that donot operate 24/7, and the dual-unified circuitinfrastructure (Category 4) lends itself to thosewhich do operate 24/7.
6.45 Enhancing the infrastructure resilience maybe achieved by adding a tertiary power source.A single-conversion UPS may be connected to
dedicated final circuits of the unified distribution.Enhancing the dual-unified infrastructure resilienceand adding additional standby generator units mayimprove the maintenance opportunities andbusiness continuity for the Category 3 or 4 riskareas.
6.46 An assessment of the potential for expansion and/orremodelling the healthcare premises should bemade, to understand how the LV distribution couldaccommodate such adaptations. This arrangementmay be appropriate for a general acute or largeacute hospital with additional support services,dependent on the assessed level of risk posed by afailure.
Dual primary and dual secondary supply unified
and dual-unified infrastructure
6.47 The LV infrastructure shown in Figure 17 has adual-primary supply, connected directly to eitherthe DNO or the healthcare sites transformer, anda dual-distributed secondary power supply alsoconnected at the intake LV switchboard. Thetransformer, standby generator, switchgear and
main cables should all be rated to take the AMDand an allowance for growth.
6.48 The first single point of failure will be at the mainLV switchboard for the unified circuits, or at thepoint of use for the dual-unified circuits. A LV
single-conversion UPS (see
may be connected to dedicunified distribution. Enhainfrastructure resilience anstandby generator units mamaintenance opportunitiefor the Category 3 or 4 risk
6.50 An assessment should be mfor expansion and/or remo
premises and how the LV dand17could accommodatarrangement may be approor large acute hospitals witservices, dependent on theposed by failures.
6.51 Figure 17 shows a potentiaa CHP plant. The schematmany potential electrical cplant. Designers and stakeideal CHP connection basblack start t