fundamentals of electrical safety

8/12/2019 Fundamentals of Electrical Safety

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Fundamentals of

electrical SafetyS .Ganesh Babu.


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A WORD ABOUT LINGERING DANGER:

Electricity above 50 volts is to be considered dangerous.

Usage of electricity has become a fundamentalnecessity.There is a consequential rise in electrical accidents andavoidable fatalities. Total safety while handling electricity by all the stakeholders needs to be ensured.It is to be understood that Electricity will not pardon

when handled carelessly. Awareness, education and training has become a mustfor those handling the supply of electricity and also theconsumers.


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Dangers fromelectricity:

Fire Hazards

Electric shocks.

Electric Flash over.

Electric faults.

Explosions .


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Indian Electricity act and rulesformulated and enforced toensure safety.

Safety of supplier and user.

Safety precautions during erection,testing, operation and maintenance.

Impose several safety requirements onelectric supply undertakings,manufacturers, contractor, owner ,user, of electrical installations /undertakings .


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PRECAUTIONS IN USE OF ELECTRICITY

Before embarking on any repair/rectification works:

All electrical circuits to be treated as live andactive.

Ensure that the spot of work is isolated andfree from external interference.

Ensure that the tools and Plants to be usedare in reliable condition in all respects.

Ensure precaution that no danger arises

from such an installation.


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Requirements for a safe

operation and usage:Sufficient rating of the equipment.Proper and good insulating material.With stand fault current or short circuit

capacity.Mechanical strength.Safe in operation.To be well maintained after installationand commissioning.The equipment and the apparatus toconform to the relevant IndianStandards.


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GENERAL HINTS ON SAFETY All electrical equipments to be treated as potentially

dangerous.

Use hand gloves while working on live system.

All voltages to be treated and handled with utmostcare.

Trouble shooting and giving connections to 440v cktsor higher rating should be done under an electricalsupervisor.Obtain work permit to work on electrical defects.



Work only on one circuit at a time.

Use adequate protective gear while working onlive circuit.

Rubber gloves should be maintained in goodcondition.

Fuses of proper amperage should be used on theline.

Non-conductive ladders should be used.

Familiarize with the conditions at hand.

Do not depend upon the insulation of the

electrical wire to give protection from shock.



Treat all electrical equipment designedfor 440 V and above as though it werelive even though it is known orbelieved to be dead or de-energised.

Keep the area around the electricalequipment dry and obtain dry board tostand on.

As far as practicable, do not work onelectrical equipment having movingparts while in operation.

Open appropriate switches and tagthem before working on electricalcircuit/equipment or dismantle anymachinery driven by electrical motors.


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Pull out all the fuses if provided asan additional precaution.

Avoid replacing fuses heavier thanthe capacity of the circuits.

All electric equipment must beproperly earthed.Broken plugs, sockets, switches,loose and worn out cables shouldnot be left as they are.Remove finger ring, bracelets andmetal wrist watch while working

with electrical equipment.Place tags on switches that areopened to permit work onelectrical equipment.


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Never close a switch without having fullknowledge about the circuit concerned andthe reason for which the tag was placed.

Never operate oil immersed switches with oilcontainer in lowered position.

Confirm yourself that that the circuit breakeris open before attempting to draw out the

circuit breaker assembly from the bus bar inmetal clad circuit breaker.

Replace all cover plates, power cabinets andother enclosures after repairs.

Use safety belts when climbing a pole andworking on an elevation.Check the safety belt before each use.


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Ensure that temporary insulation conforms togenerally accepted safety practices, withsufficient clearances over rail road, roadways

and proper type of equipment should beinstalled in gaseous areas.

Suitable barricade should be installed aroundexposed temporary high voltage electrical

equipment.

Barricade and marker must be provided forunattended open ground conduitsor tunneled location.

Watch carefully for flammable material seepageinto manhole and ensure absence of gaseousvapors that may affect the person on work.


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Ground all electrical power tools andexamine the electrical extensioncables for defects before using.

Use only 24 V for hand lamps.

Avoid making loose connection orinserting naked wire into the socket.

Ensure that earth wire is connected.

Do not make temporary connectionwith loose wire hanging around.


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ELECTRICAL SHOCK PHENOMENA

This is a sudden stimulation of the nervous system dueto flow of electric current.Can be caused by direct contact with live conductor ora flash over.

Primary shock is of such a magnitude that may producedirect physiological harm, which may result infibrillation (irregular heart beat) and respiratory tetanus(continuous contraction of muscle).Secondary shock is of such a magnitude which may notcause physiological harm but may cause involuntarymuscle reaction. Results are annoyance alarm,aversion and loss of balance due to involuntary musclereaction.


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Dry skin is much more safer than wet skinand so are dry surroundings.Skin with perspiration has low resistance.Wet walls and wet insulation are dangerous.Ear to ear shock is most dangerous.Hand to hand shock is very dangerous.

Hand to foot shock is very dangerous.Shock not involving heart, brain andinvolving only remote skin is less dangerous.Skin with cuts, wounds, bruises has low

resistance.


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Severity of electric shocksDepends on several factors

Magnitude of current flowing through part ofthe body (Ma)

Magnitude varies with time during sub -transient.

Wave form of current flowing through thebody (DC or 50 Hz AC or impulse or high

frequency)

Rate of rise of current flow (mA/ms).

Path of current through human body .


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Time duration of current flow throughthe body (milli seconds to a few seconds)

Capability of the person to withstand theeffect of shock, state of heart, brain and

health.

Phase of heart cycle at the instant of theshock

Whether the body is thrown off bymuscle reaction or gets attached bymuscle contraction/paralysis


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Prevention of shocks.Body structure must be earthed.

Conductor should beinsulated/enclosed/made inaccessible.

Clear distance to be maintained from highvoltage conductors.

Use safety insulating shoes and insulationhand gloves.Working on live line should be avoided.

Ensure that the conductor is disconnectedand discharged before commencing work.


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Safety Procedures Procedures and paper work for thefollowing should be enforced.

Permit to work

Access to work

Entry passes

Material gate pass,etc


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SafetyErection, commissioning andmaintenance should be carried out withwritten permissionThe steps to be taken by concernedauthorities to ensure safety are

Isolation of the parts from live partsduring the period of workDanger notices and safety notices atwork spot

Neighboring switches to be locked toavoid switching by third person


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Permission from authorized persons

for doing specific work should beobtained.Repair/maintenance of high voltageapparatus should be made dead andisolators opened and locked.Earthing switches to be closed andlocked. HV conductors to bedischarged and connected securely toearth

Danger boards to be displayedprominently at the switching terminalDo not use anything that is wet.


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Barrier should be provided to the sectionunder maintenance to indicate clearly themaintenance zone to differentiate it fromlive zone.

Be familiar with all sources of supply andcircuits and ensure that all feeding circuitsto the point of work are disconnected.

Ensure permit is not issued to persons notconversant with nature of work. Theperson who issues the work permit shouldensure that all basic rules of safety arecomplied with.


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Training and painting of earth metal enclosures,connection of circuits to or from live HV systems,live line testing and live insulator washing maybe carried out only in accordance with specialinstruction issued for the purpose by theauthorized authorities.

Barrier should be provided to the section undermaintenance to indicate clearly the maintenancezone to differentiate it from live zone.Be familiar with all sources of supply and circuits

and ensure that all feeding circuits to the pointof work are disconnected.


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Ensure permit is not issued to persons notconversant with nature of work. Theperson who issues the work permit shouldensure that all basic rules of safety arecomplied with.

Cleaning and painting of earth metalenclosures, connection of circuits to or fromlive HV systems, live line testing and liveinsulator washing may be carried out onlyin accordance with special instructionissued for the purpose by the authorizedauthorities.


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Live line work on HV over head maybe carried out in accordance withrules i.e.:

by trained personnelwith recommended approved tools and with allprecautionsThe work should be carried out in presence ofsenior authorized person and with dueapproval to carry out the work

Check safety clearance between nearest livepoint and other physical objects duringmaintenance viz. ladders, platforms, liftingdevices, metal bars, etc.


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Keep earthed screenbetween live zones andmaintenance zonesLive line working shouldonly be carried out if shut

down is not permissible andif trained personnel for suchwork are available

Aim at safety proceduresNot even a single personshould get injuredEliminate electric shocks


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Installation of earth system

Generally earthing mat is consideredthe first activity in sub-station orother electrical installation work

Earth mat work includes burying ofearth rod, earthing mat, risers, etc.

All recommended parts are to beconnected to the earth mat to keep

the step and touch potential at safelevel.Ensure all the parts for the systemabove the ground level are carefully

laid and connected


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Follow strictly the erection documentationfor :Structure earthing

Tower earthing and earthing of over headearthing shield Apparatus and cabinet earthingEarthing switches terminalDisconnector earth switch terminalEquipment earthingTransformer neutral earthingTransformer tank earthingSurge arrestors terminal earthing

Cable rack earthingCapacitor neutral earthingShunt reactor terminal earthingEarthing of fencing, doors, screens, lampposts, cabinets, etc.


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Ensure the sequence of operation ofcircuit breaker, isolator and earthingswitch: While opening a circuit Open circuit breaker first

Open isolator nextClose earthing switch

And While closing the circuit:

open the earthing switch first, close the isolator, then close the circuit breaker


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Safety Provisions applicable to mediumvoltage/high voltage

All conductors except OH line should becompletely enclosed in metallic casingwhich is electrically and mechanicallycontinuous

All metal work, enclosures, supports of theinstallation other than the conductor shouldbe connected to the earthing system.Electrical installations/apparatus whereinflammable materials are

produced/stored/handled should complywith the requirements of flame proof, dusttight, tightly enclosed electrical fittingsdepending upon the hazardous zone as perrelevant specification.


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Sub-station installation

Whether the installation is in accordancewith the relevant standards/approveddrawingsPhase to phase and phase to earthclearances are as per standards

All equipment are efficiently earthed andconnected to required number ofelectrodesThe required ground clearance to liveterminals shall be ensuredSuitable fencing with gate and lockablearrangement is providedRequired number of caution boards, firefighting equipment, operating rod, rubbermats, etc. are kept in sub-station


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To ensure earth electrodes are of GI pipe orCI pipe or copper plate. For earthconnection brass bolts and nuts with leadwashers are provided in the pipes and theplatesEarth pits are free from rubbish and dirt andstone jelly and earth connection are visibleand easily accessibleHT and LT panel and switch gear are allvermin and damp proof and all unusedopenings or holes are blocked properlyThe earth bus bars have tight connection andcorrosion free joint surfacesControl switch fuses/isolating handle areprovided at an accessible height from theground

Adequate head room is available for indoortransformers for easy maintenance andtopping of oil etc


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Ensure that the bushing are free fromcracks and dust

Accessories of transformer such asbuchholz relay, breathers, vent pipe, etc.are in order.Connection to gas relay are in orderOil and winding temperature are set forspecific requirement in the transformersIn the case of cable cellars, adequatearrangement to pump out water due toseepage or other reasons, should beensured.

All incoming and outgoing circuits and HPand LT panel are clearly and indelibly labledfor identification.Every telecommunication line on supportcarrying a HV or EHV line shall, for thepurpose of working thereon be deemed tobe a HV line


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EQUIPMENT GROUNDING All electrical equipment, and systems should

be grounded in accordance with IS:3043 :1987 and IEC Standards. The conductor usedfor grounding should conform to thefollowing criteria:

Be permanent and continuous.Facilitate operation of circuits protectivedevices.Shall have sufficient low impedence to limit

the voltage to the ground to a safe level atall frequencies, and anticipated faultcurrents..Of sufficient capacity to carry the faultcurrent during the period of fault.


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The equipment grounding conductor shall be ofsuitable size adequate to carry the fault current.Increase in conductor size is recommended incase of long runs of the conductor so as to limitthe voltage drop to 5% of the rated voltage.The portable equipment Should be grounded bymeans of a separate green colored equipmentgrounding conductor within portable chord.

The metal enclosures of all electric equipmentincluding temporary power distn. Boards shouldbe connected to earth and the earth resistanceshall be consistently monitored an so also thecontinuity of the earthing.Temporary power distribution boards shall beprovided with suitable fire fighting supports.Residual current devices (earth leakage circuitbreakers) at the point of supply for 240v hand

held portable tools/equipments shall berovided.


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EQUIPMENT AND PERSONNEL :GUIDELINES.

Grounding of metal parts to continuouslydischarge static current.Wrist straps and other connections used toground the employees should be solidly

grounded where static safe workstations areused for semi-conductor, electronic orexplosive work sites.Bonding will equalize the potential betweentwo adjacent non current conducting metalenclosures. Only approved grounding clampsare to be used for static bonding andgrounding. Alligator clamps are to to be used.Construction aiding power equipments shall notbe exposed to moisture/ wetness, and shall notbe operated when wet.


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All tools and power operated supports shall beinspected regularly in a planned manner. Theleads, connecting terminals, earth chord andcontrols shall be included in the inspection.

Persons engaged on electric equipment shallbe provided with electric safety shoes andrubber gloves/apron.

Only trained, qualified and authorized staffshall install or repair electrical equipment.

No temporary repairs to electrical system shallbe encouraged.

Correct rating of the fuses shall beensured.


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Emergency Assistance and Rescue A serious electric shock

results in any of thefollowing conditions:

Serious injury resulting in loss of

consciousness, significant trauma

Altered mental status like confusion,low/slurred speech

Other injuries such as lasceration,muscle strain, burn, etc.


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These incidents should be reported tothe safety team in the site which shallbe trained to administer first aid andarrange for medical assistance in theshortest time possible.

In case of emergency, cardio

pulmonary resuscitation (CPR)performed by only trained personnelshould be initiated

The reason for the electric shock afterit is notified shall be investigated forthe reasons and remedial measures.


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Training All personnel carrying out electrical

work shall be periodically trained andtraining should be documented withrespect to specific equipment andtasks for which the employees isqualified.

On the job training is always anecessary component of aqualification program.

The depth of training and quantum oftraining to be provided should bedetermined by the hazardsassociated with the personnelsrespective tasks.


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Other subjects such as :

Electrical safety requirement for work places

Use of testing and measuring equipment

Safety plans and work authorization documents

Use and care of personal protective equipment

Hazard categories and personnel requirements


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In addition to the training provided for carryingout electrical related jobs and non electricalworkers, whose job assignment require them towork close to exposed circuit electrical circuitsoperating at 50 V or more to ground, shouldreceive supplementary training in the followingsubject areas :-

The proper handling of portable tools and appliancecords.Procedures for resetting over current protective devices.Techniques for approaching distances to overheadconductors.The meaning of electrical safety warnings and barriers.Electrical hazards associated with water.The proper response to electrical shock.


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Cross boundary Safety Rules shall be

prepared jointly by the entitiesconcerned to cover electrical safety,where HP and EHP equipmentbelonging to more than one entity areinstalled at a location. When de-energization of equipment or line in asystem of one entity, when needed tobe carried out by the switchgearlocated in the system of another entity,these safety rules shall be adhered to.


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Where an electric spark can cause anexplosion or fire, the entire process,space and equipment shall be covered byElectrical Safety Rules, even if theprocess is mechanical or chemical bynatureSafety to building, structures, andmechanical equipment related toelectricity directly or indirectly shall becovered under the Safety Rules andProcedures.Safety audit shall be conducted by allentities for the installations in the

respective jurisdiction for monitoring andreviewing the implementation of SafetyStandards.


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Periodical Inspection and testing ofinst allation:

Where an installation is already connectedto the supply system of the supplier, everysuch installation shall be periodicallyinspected and tested at intervals notexceeding 5 years either by the electricalinspector or by the supplier as may bedirected by the state government on itsbehalf, or in the case of installationsbelonging to are under the control ofcentral government, in mines, oil fields,and railways. The periodical inspection andtesting of HV and EHV installationsbelonging to the supplier shall be carriedout at intervals not exceeding 5 years bythe inspector or any officer appointed toassist the inspector.


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Provision for isolation of supply A switch, circuit breaker, isolator, or a dis- connector shall be provided fordisconnecting supply to any feeder, pieceof equipment, machine, apparatus, or anyitem of installation.Identification tags for the switch shall beclearly painted / labeled.The switch shall be placed at anaccessible place.

All employees shall be made to familiarizewith the switch and apparatus that itcontrols.


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Safe access and safe exit

All installations such as sub station,engine room of the generating

station, electrical rooms of factoriesshall have safe access and safe exitpassages.

Insulation to be provided to all conductors


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Insulation to be provided to all conductors

All conductors to be provided with insulation withthe following minimum specifications:-

Adequate thickness to withstand system voltage withsafety margin

Withstanding impulse voltage caused by lighteningsurges

To withstand maximum temperature at full loadsconsidering the maximum ambience temperature at thelocation

Resistant to chemical corrosion and atmosphericcondition

Retention of the above mentioned qualities over a periodof life


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Electrical maintenance

Maintenance on electrical equipment tobe done by qualified and skilledpersons.No item shall be omitted duringreassembly, and no foreign materialsshall be left inside the equipment.Defects noticed earlier while inoperation and during maintenanceshall be rectified

Installation of all partly inspected anddamaged installations replaced.The IR value shall be measured and forlow values of IR. remedial action shallbe taken.


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All loose contacts shall be rectified All corroded, eroded and damagedparts shall be replacedContacts in circuit breakers shallbe inspected and replaced ifnecessaryThe IR value of oil in the

transformer, CT and circuitbreaker shall be measured andreplaced/filtered in case ofnecessity.Effectiveness of earthing shall beensuredMaintenance work shall be carriedout in adequate lighting,ventilation and working space


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STAFF DISCIPLINEThe duties shall not be carried out by the staff

under intoxicated conditionThe in - charge shall ensure that medically unfitstaff members do not handle electrical apparatusSmoking shall be prohibited where electricalinstallations are there, in battery rooms andwhere inflammables are stored.Persons suffering from diseases like epilepsy,Parkinson disease, paralysis, etc. shall not workstanding on structures, scaffolds, ladders or any

elevated location or in the vicinity of waterreservoir, well and rotating equipmentUnauthorized persons shall not be allowed to stayin locations of electrical installations


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All work shall be pre planned and

haste shall be avoidedWork shall not be permitted to becarried by persons who are tiredor exhaust on complex apparatusor hazardous equipment

All workmen shall carry out workwith awareness of safety rulesand due concentration

All staff members shall be

encouraged to discuss and offerrelevant suggestions forimproving safety procedures


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All workmen shall aim at :-

Safety for fellow workmen

Safety for public

Protection of equipment

Good quality of work to ensurefuture safety


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G l f d l


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General safety and clearancesNeutral Conductor Ensure the electrical continuity

The cross section shall not be less thanhalf of the phase conductor in a 4 wiresystem and less than that of phaseconductor in case of a 2 wire system

The neutral shall be earthed at thetransformer


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Lines at other places:-Low, medium and high voltages Up to and including

11 KV:-If bare 4.6 Mtrs

As above but insulated 4.0 Mtrs Above 11 KV up to 33 KV 5.2 Mtrs

33 KV to 66 KV 5.3 Mtrs66 to 132 KV 5.9 Mtrs132 KV to 220 KV 6.8 Mtrs220 KV to 400 KV 8.6 Mtrs400 KV to 765 KV 12.0 Mtrs

Note: In general clearances in air shall becorrected for altitude.


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Clearance from buildings:-

Vertical clearance: Not less than 2,5 Mtrs.Shall be measured from the highest pointof roof and lowest catenary point of theline.

Horizontal clearance:Not less than 1.2 Mtrs.Shall be measured at maximum deflectionfrom the vertical due to wind pressure.


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Clearances for low and MV lines frombuildings:-

The vertical clearance shall not be less than 2.5 Mtrs.The horizontal clearance shall not be less than 1.2Mtrs.The vertical clearance shall be measured from thehighest point of the roof and at the lowest catenarypoint of line. At any point along the line the verticalclearance shall not be less than the stipulated value.

The horizontal clearance shall be measured atmaximum deflection from the vertical due to windpressure.

Clearances of HV and EHV lines from buildings:-


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Clearances of HV and EHV lines from buildings:-For vertical Clearances:

For high voltages up to and including 33 KV:- 3.7 Mtrs

For EHV line:- 3.7 Mtrs +0.3 Mtrs for every

additional 33 KV or part thereof.

Horizontal clearance on the basis of maximumdeflect ion of the conductor due to wind pressure, shall not be less than:-

For HV lines up to and including 11 KV:- 1.4 Mtr

11 KV and up to and including 33 KV:- 2.1 Mtr

EHV line:- 2.1 Mtrs +0.3 Mtrs for every

additional 33 KV or part thereof.

Transporting or storing of materials


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Transporting or storing of materialsnear OH lines :-

No rods, pipes or similar material shall be takenbelow or in the vicinity of any bare OHconductor/lines if they are likely to infringe theprovisions for clearance

They shall not be brought within a distanceequal to the flash over distance plus areasonable margin

No material, sand, stone, earthwork, agricultural

produce or grass shall be piled, dumped, orstored below or in the vicinity of bare OH linewhich may reduce the required safetyclearances. Similarly, trees shall not grown inthe vicinity of OH lines


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Crossing or location of telecom and power lines:- Whenever an OH line crosses or in theproximity to any telecom line, whoever laysthe line later shall arrange to provideprotective devices/guarding arrangement.One month notice shall be given by the

telecom authorities for laying a telecom lineacross an existing OH power line.The telecom authorities shall also providerelevant details of protection and drawings tothe utility.

A similar procedure will follow when the utilitylays his line which needs a crossing.

Angle of crossing shall be 60 or more.

Minimum clearances between power line and


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Minimum clearances between power line andcommunication line

Voltage Minimum clearance(Mtrs)

LV and MV 1.8 650 V to 11 Kv 2.3

11 KV to 33 KV 2.6

33 to 132 2.75 132 to 220 4.57

220 to 400 4.88

Crossing of OH power lines


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Crossing of OH power linesS.No Nominal System Voltage in KV

Min clearance in Mastrs between line ofvoltage mentioned in 1st col andanother line at a nominal systemvoltage (in KV) of

11 to66

110to

132

220 400 765

1 Low and Medium voltage 2.5 3.1 4.6 5.5 8.02 11 to 66 2.5 3.1 4.6 5.5 8.03 110 to 132 3.1 3.1 4.6 5.5 8.04 220 4.6 4.6 4.6 5.5 8.05 400 5.5 5.5 5.5 5.5 8.06 765 8.0 8.0 8.0 8.0 8.0

Note : Guarding shall be provided if the clearance between circuits isless than the prescribed values.

However, the clearance shall not belower by more than 20% even when guarding is provided.

Railway Crossing


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The Angle of crossing shall be 60 ormore.The crossing span shall not exceed80 of the corresponding normaldesign.

The minimum prescribed clearancesbetween the lowest power conductorand the railway track and themaximum sag condition shall bemaintained.The minimum distance betweenfooting of the nearest tower and therailway track shall not be less than1.5 times the height of the tower.


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Clearances in out door installations


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VoltageKV

For various items ofequipment and rigid

conductors in air

Phase to phase spacing inisolator and switches

Phase toPhase(cm)

Phase toEarth(cm)

Isolator(cm)

Switch with arcinghorn (cm)

400 400 350 415 500 220 335 167.5 335 396 132 201 122 257 366 66 122 76 153 214 33 92 61 76 122 22 61 46 76 107 11 46 31 61 92

04 38 31 - -

Clearances in open type out door switch gear


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Rated

VoltageKV

Minimumclearance to earth

in air (cm)Minimum clearancebetween phases (cm)

Safety

SectionalClearances(cm)

6.6 14 18 30511 18 23 305

22 26 33 27533 38 43 27766 69 79 305

110 87 99 335132 107 122 351220 178 206 428400 385 440 650

p yp gand bus bar connections


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RatedVoltage KV

Minimumclearance to earth

(cm)

Minimumclearance

between phases(cm)

Upto 0.6 1.2 1.23.3 1.2 2.06.6 2 2.511 2.5 422 4.5 6.533 6.6 9

Minimum clearance in bus bar in oil or compound

Min clearances in air in indoor switchgear


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Rated

VoltageKV

Minimum

length ofInsulator(cm)

Minimum

clearance toearth (cm)

Minimum

clearancebetweenphases (cm)

Up to0.415

2 1.6 2

0.6 2 2 23.3 5 5 56.6 9 6.5 9

11 12.5 7.5 12.515 15 10 16.522 20 14 2433 21 22 35

Min clearances in air in indoor switchgear

Clearance between phases between phase and earth


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Rated VoltageKV Minimumclearance

to earth(cm)

Creepagedistance toearth overcable end(cm)

Minimumclearance

between phases(cm)

Upto and

including 11KV

5 13 5

Above 11 KVand upto andincluding 22KV

7.5 16.5 10

Above 22 KVand upto andincluding 33KV

10 20 12.5

Clearance between phases, between phase and earth,and creepage distance to earth


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The minimum clearancesbetween lines and guardwires shall be as follows :-

Up to 33 KV 1.20 Metres

132 KV 1.75 Metres220 KV 2.00 Metres 400 KV 3.00 Metres765 KV 4.00 Metres

Minimum clearances between phase and tower material


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Voltage KV Clearance cm

Up to 22 3033 39.4

66 67.5132 123.6

220 198.4

400 351.4765 661.7

Minimum clearances between phase and tower materialAt the time of maximum deflection due to wind pressure


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Voltage KV Clearance

cmUp to 220 300400 453

Clearances over river crossings under maximum floodingconditions where there is no navigation

fundamentals of electrical safety

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