Underground Electrical Systems

Safe Practice Guide

ihsa.ca

The Infrastructure Health & Safety Association

Safe Practice Guide

UNDERGROUND ELECTRICAL SYSTEMS

Foreword

This Guide designates practices that should be fol-lowed by the member firms of the InfrastructureHealth & Safety Association (IHSA) when doing workon underground electrical plant. This Guide is notdesigned as a training manual, but contains informa-tion, best practices and general recommendationsdeemed appropriate to perform a job in a responsibleand safe manner.

The contents of this Safe Practice Guide, includingadvice, recommendations and procedures, are provid-ed as a service by the Infrastructure Health & SafetyAssociation. No representations of any kind is madeto any persons whatsoever with regard to the accura-cy, completeness or sufficiency of the information con-tained herein. Any and all use of or reliance on thisSafe Practice Guide and the information containedherein is solely and entirely at the user’s risk. Theuser also acknowledges that the safe practicesdescribed herein may not satisfy all requirements ofOntario Law.

The Infrastructure Health & Safety Association wishesto express its appreciation to those who assisted inthe preparation of this Guide.

All rights reserved. This publication may not bereproduced, in whole or in part, without the expresswritten permission of the copyright owner.

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Acknowledgments

The Infrastructure Health & Safety Associationwishes to express its appreciation to the following industry partners for their assistance in completingthis Safe Practice Guide:

Colin Barron, Cablemaster Inc.Bob Erwin, AMAC EquipmentTerry Irwin, CanTranRon Smith, Thomas & BettsDan Watters, Hydro Ottawa

Some photos are courtesy of Condux International Inc.

This Safe Practice Guide is dedicated to the workers,both past and present, who build and maintain elec-trical underground systems. IHSA also wishes to con-vey a special recognition to Doug Williams and thelate Charles Tallon. Both men dedicated their careersat IHSA to the pursuit of quality education and train-ing for underground workers, with the goal of zeroworkplace injuries.

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TABLE OF CONTENTS

Underground distribution terminology 6

SECTION ITYPES OF UNDERGROUND SYSTEMS

100 Introduction 16

101 Radial system 16

102 Loop system 17

SECTION IITHEORY AND UNDERGROUND CABLES

200 Introduction 20

201 Cable ampacity 20

202 Cable shielding 20

203 Cable components 21

SECTION IIIINSTALLATION OF UNDERGROUND CABLES

300 Introduction 26

301 Records/mapping 27

302 Direct buried 28

303 Conduit installation 29

304 Conduit roping 29

305 Mechanical rodding 30

306 Pneumatic rodding 31

307 Cable installation 33

308 Maintenance chamber/vault hardware 38

309 Installation on pole 40

310 Cable terminations 41

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311 Splices 44

312 Installation of elbow connectors 45

313 Working on underground cable installations 48

SECTION IVTRANSFORMERS AND SWITCHGEAR

400 General 50

401 Surge protection 51

402 Transformers 51

403 Switchgear 54

SECTION VSWITCHING AND GROUNDING

500 General 60

501 Equipment required 60

502 Tools 61

503 Switching 62

504 Tests 63

505 Temporary grounding 64

506 Cable testing 65

SECTION VITROUBLESHOOTING

600 General 68

601 Initial communication 68

602 Current mapping 68

603 Types of systems 69

604 Types of faults 69

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SECTION VIICABLE AND FAULT LOCATING OF URD CABLES

700 General 76

701 Electro-magnetic induction 76

702 Signal frequency 78

703 Types of signals 79

704 Applying an active signal 79

705 Direct connection 79

706 Induction 80

707 Clamping the signal 81

708 Passive signals 81

709 Cable locating tips 81

710 Fault locating 83

711 Primary fault locating 84

712 Secondary fault locating 86

METRIC/IMPERIAL CONVERSIONS 87

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UNDERGROUND SYSTEM TERMINOLOGY

AmpacityCurrent carrying capacity, expressed in amperes, of awire or cable under stated conditions.

AmbientConditions existing at a test or operating locationprior to energizing of equipment (e.g., ambient tem-perature).

American Wire GaugeA standard used in the determination of the physicalsize of a conductor determined by its circular milarea. Usually expressed as AWG.

AmpereThe unit used for measuring the quantity of an electriccurrent flow.

Anti-oxidantA substance which prevents or slows down oxidationof a material.

ApparatusAll equipment pertaining to the generation, transmission, distribution and use of electricity.

BarrierA device or procedure that effectively keeps a workeraway from a hazard.

Bend RadiusThe minimum bending radius for underground cablesas per manufacturers’ specifications.

BILBasic Insulation Level – the voltage the equipment willaccept before sparkover.

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BushingA receptacle that allows cables to be connected toapparatus.

Cable RackA device, usually secured to the wall of a mainte-nance hole, cable raceway, or building, to providesupport for cables.

Capacitive ChargeElectrical energy that remains in conductive and insulated components of a primary cable after it hasbeen disconnected from all sources of dynamic ener-gy.

Circular MilA term used to define cross sectional areas using amathematical shortcut in which the area of a roundwire is taken as a diameter in mils (0.001 in.)squared.

Concentric Neutral CableA cable with a concentric, composed of metallic wiresapplied over the insulation or insulation shielding. Theconcentric wires perform the function of a neutral.

ConductivityA term used in describing the capability of a materialto carry an electric charge. Usually expressed as a percentage of copper conductivity – silver being onehundred per cent.

ConductorThat part of a cable, overhead line or apparatusintended to conduct the flow of electrical energy.

Cross LinkedManufacturing process that significantly improves theoverall performance of polyethylene insulation.

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Current Carrying CapacityThe current a conductor of given size is capable of carrying safely without exceeding its own insulationand jacket temperature limitations.

CutoutA fused switch either overhead or underground.

Dead-end Plugs — Insulating CapA manufactured device to insulate an open recepta-cle.

Dead Front or Elbow ConnectedAny type of equipment (transformers, multi-taps andswitching cubicles) that utilize elbows. The term deadfront means that no full line potential parts areexposed (e.g., submersible and padmount transform-ers). Elbow connected equipment has no exposedcomponents when in the normal operating position.

DielectricAn insulating (non-conducting) medium.

Direct BuriedAn underground cable that is installed in the groundwith no protective covering other than sand and fill.

Disconnect(ing) SwitchA switch used for closing, opening, or changing the connections in a circuit or system, or for isolating purposes. It has no interrupting rating, and is intend-ed to be operated only after the load has been dis-connected by some other means.

Drain WireIn a cable, an uninsulated wire laid over the compo-nent or components and used as a ground connec-tion.

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DuctA tube used to install and protect underground plant.Its material may include plastic, PVC, fibres etc.

ElbowLoadbreak or non-loadbreak, a manufactured devicewhich allows cables to be connected and disconnect-ed to underground components (e.g., transformers).

ElectromagneticReferring to the combined electric and magnetic fieldscaused by electron motion through conductors.

EPREthylene propylene rubber. A form of material used inthe cable industry either as insulation or when carbon particles are added as a semi-conducting material.

EUSRThe Electrical Utility Safety Rules, published by theInfrastructure Health and Safety Association.

FerroresonanceA high voltage phenomenon which may occur onthree phase applications when the inductance of theferrous core of a transformer and the capacitance of ahigh voltage underground cable are equal and con-nected in series. As much as ten times the normalvoltage may be present.

GroundingConnecting the components of an electrical system toground potential using approved equipment.

Ground BusA bus to which the grounds from individual pieces ofequipment are connected, and that in turn, is con-nected to ground at one or more points.

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Ground GridA system of bare metallic conductors on or below thesurface of the earth, connected to ground.

InsulationA material having good dielectric properties which isused to separate close electrical components, such ascable conductors or circuit components.

Insulation RatingThe property of an insulating material which resists electrical current flow when a potential difference isapplied.

LIS Load interrupter switch. A device that interrupts theflow of electricity while under rated loads.

Live FrontAny type of transformer, switch gear, or load centrewhere full line potential is exposed when the door isopened (e.g., pole transformer and load centres).

LoadA device that consumes or converts the power deliv-ered by another device.

LugA term commonly used to describe a termination, usually pressed or soldered to the conductor, with provision for bolting to a terminal.

Maintenance Chamber/VaultA chamber or enclosure used in an underground electrical distribution system to house electrical apparatus, or the entranceway thereto.

Metal CladStation equipment with a metal enclosure around it(e.g., station breakers and bus tie).

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MilOne one-thousandth of an inch.

Nitrogen GasA gas that is often used as a blanket over oil in apower transformer to keep moisture and oxygen from contaminating the oil.

OhmA unit of electrical resistance, specifically the amountof resistance overcome by one volt in causing oneampere to flow.

OxidationA chemical reaction that occurs when metal reactswith oxygen, producing a layer of oxide on the sur-face. The oxide layer resists the flow of electricity andcan create heat.

PolyethyleneA thermoplastic material derived from polymerizationof theylene gas. Basically, pure hydrocarbon resinswith excellent dielectric properties.

Pot HeadA type of termination usually used in conjunction withlead cable (PILC), either single phase or three phase.It seals against moisture and leakage of compound.

PVCPolyvinyl chloride. A general purpose thermoplasticused for wire and cable insulations and jackets.

Riser (Dip Pole)A transition installation between underground cableand the overhead system.

Splice (Joint)The process by which cables are joined together to manufacturers’ specifications.

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Stress ConeA means of providing extra insulation at the point ofgreatest stress in the cable.

Stress LinesInvisible lines of force set up in a cable by electro-magnetism which act to break down insulation unlesscontrolled.

SubmersibleConstructed to be successfully operable when submerged in water under specified conditions of pressure and time.

SystemPhysical layout of an underground plan (e.g., loop orradial, overhead or underground).

TerminationThe method of providing a weatherproof transitionfrom the cable to equipment, while relieving stressand controlling tracking.

ThermoplasticA classification of resin that can readily be softenedand re-softened by repeated heating.

TDRTime domain reflectometer. Equipment used to locatefaults and display the fault distance on a graph.

TransformerEquipment designed to either step up or step down voltage levels as required.

TR-(XLPE)Tree retardant. An additive to cable insulationdesigned to slow the growth of cable trees (insulationbreakdown).

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URDUnderground residential distribution. Commonlyrefers to all underground installations.

UWPCUtility Work Protection Code. The written proceduresto establish an isolated tagged and/or locked out con-dition for work.

Voltage DropA term expressing the amount of voltage loss from original input in a conductor of given size and length.

XLPECross linked polyethylene – a common form of insulation used on underground cables.

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SECTION ITYPES OF UNDERGROUND SYSTEMS

100 Introduction

101 Radial system

102 Loop system

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SECTION ITYPES OF UNDERGROUND SYSTEMS

100 INTRODUCTIONThe growing use of underground electrical systemsmeans that today's utility personnel should under-stand both the theory behind and the practical use ofunderground equipment. As these underground sys-tems become more complex, utility workers willrequire more training to keep abreast of the continu-ally changing technology and to avoid unsafe actsand work practices.

Depending on the location, underground systems maybe supplied directly from a substation or an overheadline. If energized from a substation, the undergroundcables will be connected at the station by a stresscone/termination and protected in the event of ashort circuit or overcurrent by a station breaker.

If energized overhead, the pole where the under-ground cable taps onto the line is called a riser or dippole. The cable running down the pole is either pro-tected by a cable guard or enclosed in a conduit.

The underground cable makes the transition to the overhead line via a switch, lightning arrestor and acable termination called a stress cone or pot head.

101 RADIAL SYSTEMUsually the simplest and least expensive type of sys-tem, radial circuits are supplied from one source onlyand are susceptible to relatively long interruptions toservice in case of cable failure. (See Figure 1)

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102 LOOP SYSTEMThe preferred underground system has a loop feed,as shown in Figure 2. The loop system consists of asingle circuit run successively to a number of trans-former installations and returned either to the originalsource or to a different source, provided it is compati-ble. It is common practice to operate the midpoint orthe "loop open point" – thus the term "normally openloop."

While more costly to install, this system can be dividedinto sections, making for easier maintenance and shorter outage time in case of cable failure, as well asbetter voltage regulation and system reliability.

Figure 1: Radial System

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Figure 2: Loop System

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SECTION IITHEORY AND UNDERGROUND CABLES

200 Introduction

201 Cable ampacity

202 Cable shielding

203 Cable components

SECTION IITHEORY AND UNDERGROUND CABLES

200 INTRODUCTIONHigh voltage cables used in underground systems areselected on the basis of the ampacity and voltagerequirements of the circuit in which they are to beinstalled.

Cables used for underground installation are general-ly either paper insulated lead covered (PILC) or a soliddielectric type. Examples of a solid dielectric cablemay be of a cross linked polyethylene (XLPE) construc-tion or ethylene propylene rubber (EPR).

The conductor, which makes up the core constructionof the cable, can be either copper or aluminum andmay be supplied with stranded or solid wire. For spe-cific details, contact the manufacturers of the product.

201 CABLE AMPACITYThe ampacity requirements of cables and conductorsused are fairly straightforward, regardless of the operating voltage. The ampacity will depend onwhether the conductor is in duct, direct buried, or inthe air. (See Cable Ampacity Chart)

202 CABLE SHIELDING

High voltage cables must be shielded to ensure thecable is protected. Power cable shielding can bedefined as the practice of controlling the electro-mag-netic field of the cable.

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Shielding in the high voltage cable is done in twoparts. (See Figure 3) The first is the conductor shield,which smoothes out the irregularities of the conductorso that the insulating material is not subject to a non-uniform stress pattern. The second shielding is extrud-ed over the insulating material surface to act as a bedfor the metallic ground. Both materials used for theshielding are usually polyethylene with carbon parti-cles added to make it semi-conductive.

203 CABLE COMPONENTSConductorThe purpose of the conductor is to support up to itsrated amount of current flow. The conductor may beeither copper or aluminum. Most are stranded but asolid conductor is also available.

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Figure 3: Stress relief using the insulation and conductor shield.

Stress lines withoutshields

Stress lines with theshields

CABLE AMPACITY CHART

Cable Rated < 28 kV Cable Rated > 35 kV

Size Buried In Duct Duct In Air Buried In Duct Duct In Air(Awg/kcmil) In Air In Air

4 Cu 135 115 100 1254 Al 130 110 95 120

2 Cu 210 180 155 1952 Al 165 140 125 155

1 Cu 240 205 180 2251 Al 185 160 140 175

1/0 Cu 275 230 210 260 275 230 210 2601/0 Al 215 180 165 205 215 180 165 205

2/0 Cu 310 265 245 300 310 265 235 2952/0 Al 245 205 190 135 245 205 190 235

3/0 Cu 355 300 280 345 355 300 275 3453/0 Al 275 235 210 265 275 235 210 265

4/0 Cu 395 320 315 390 385 330 305 3804/0 Al 315 270 250 310 315 275 250 310

250 Cu 420 345 340 420 425 350 335 420250 Al 330 290 265 330 330 295 265 330

350 Cu 470 395 380 475 470 395 380 475350 Al 400 340 325 405 400 345 325 405

500 Cu 515 420 435 535 520 440 430 540500 Al 460 385 385 480 460 395 385 480

750 Cu 580 475 505 625 590 495 510 640750 Al 525 430 455 570 525 450 455 570

1000 Cu 640 525 580 715 625 525 555 695

1000 Al 570 470 510 635 570 485 510 635

Knowing the conductor size and whether the conductorbody is of a standard round construction, compressedconstruction or compact is important. This has an impacton the type of terminations or sleeves used.

Conductor ShieldingThe primary function of conductor shielding is to providea smooth surface and straighten any irregularities of the

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conductor. Another function is to assist with electricalstress relief on the cable. The physical properties ofthis material make it semi-conducting by adding car-bon particles to a cross-linked polyethylene material.

InsulationThe insulating materials most commonly used are:- Thermosetting cross-linked polyethylene (XLPE)- Tree retardant cross-linked polyethylene (TR-XLPE)- Ethylene propylene rubber (EPR)

The insulation is extruded to a thickness required towithstand the voltage at which the cable will be energized, above ground or phase potentials.

Insulation LevelsThe insulation for primary underground cables is generally constructed to two insulation levels, and manufactured for specific applications:

100 per cent level: the cable manufactured to this specification is best applied in a system with relay protection to provide ground fault clearances as rap-idly as possible, in may cases within one minute.

133 per cent level: a cable manufactured to this specification may be applied in situations where theclearing time of the 100 per cent level cannot be met.

Below are examples of cables manufactured for spe-cific voltage levels but that have different insulationdiameter thicknesses due to the different insulationlevels:

15 kV - 100% Ins. Level: 4.45 mm (0.17 in.)15 kV - 133% Ins. Level: 5.46 mm (0.21 in.)28 kV - 100% Ins. Level: 7.11 mm (0.28 in.)28 kV - 133% Ins. Level: 9.54 mm (0.37 in.)

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Insulation is generally measured in mils. It is impor-tant to know the insulation level of the cable, as thiswill determine which termination or splice kit shouldbe used.

Insulation ShieldThe insulation shield is made of the same materialused for the insulation shield. The main purpose ofthe conductor shield is to ensure uniform electricalradial stress relief at the insulation surface. (Refer toFigure 3)

Concentric NeutralsConcentric neutral strands provide a return path forthe system neutral. The concentric neutrals will alsoprovide some mechanical protection for the insulatedconductor and become the return of current path tostation relay protective system or some other form ofover-current protection (fusing). This will aid in theevent of a dig-in on the cable.

JacketPolyvinyl chloride (PVC) and polyethylene are thermo-plastic materials commonly used in jacket construc-tion. The jacket will provide protection againstmechanical and chemical damage. It is also meant tohold the concentric neutrals against the insulationshield. Cable construction can also include unjacketedcable applications.

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SECTION IIIINSTALLATION OF UNDERGROUND CABLES

300 Introduction

301 Records/mapping

302 Direct buried

303 Conduit installation

304 Conduit roping

305 Mechanical rodding

306 Pneumatic rodding

307 Cable installation

308 Maintenance hole hardware

309 Installation on pole

310 Cable terminations

311 Splices

312 Installation of elbow switches

313 Working on underground cable installa-tions

SECTION IIIINSTALLATION OF UNDERGROUND CABLES

300 INTRODUCTIONEnsure proper work area protection (in compliancewith current legislation) is used to protect workersfrom vehicular traffic.

Accurate phase markings are essential. Ensure that allworkers understand the phase markings that are tobe used and that those markings match the engi-neered drawings of the project.

When cables are to be installed in proximity to ener-gized apparatus, work area protection must be incompliance with the Utility Work Protection Code andthe Electrical Utility Safety Rules.

Setting and following high quality standards is partic-ularly important when installing underground plantdue to the high cost of maintenance and repair.Proper installation procedures improve system reliabil-ity, which reduces outages and the hazards associatedwith repair.

Most incidents that result in serious injury (or have thepotential for serious injury) occur on undergroundplant during after hours "emergency" situations (i.e.,when cable has failed). By limiting exposure to thosesituations through proper installation, we also limitthe possibility of an incident.

When trenching for underground plant installation, itis very important to observe proper sloping tech-niques. Many installations require only a relativelyshallow trench (less than 1.29 m / 4 ft.). However,when final grades must be altered or other installa-

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tion circumstances dictate, deeper trenching may berequired. All trenches must comply with current legis-lation. Particular attention should be given to trench-es with high water content.

Water is the primary cause of reduced cable life.When installing any type of underground cable, be itprimary or secondary, it is very important to keep thecable dry. To do so, make sure all ends of all cablesare sealed with heat shrink caps or SAPT tape forwaterproofing during installation and storage.

Avoid damaging the cable by subjecting it to roughtreatment. For example, the outer jacket can be damaged when the cable is dragged across theground.

Do not bend the cable in too tight an arc. Always fol-low the manufacturers’ minimum bend radius specifi-cations. They are designed to prevent the layers of thecable from separating and creating voids, which mayprovide an area for moisture to gather.

301 RECORDS/MAPPINGIt is important to maintain the records and mappingof your system. At minimum, you should include the following:- Duct size- Duct material- Cable size- Number of cables- Cable type- Bends and radii- Tensions experienced during installation

302 DIRECT BURIEDDirect buried installations have specifications thatneed to be followed. A typical installation will havemany utilities using the same trench, thus the namejoint use trenching. Generally, industry practice is:

TOP: Telecommunications (phone and CATV)

MIDDLE: Secondary conductorsBOTTOM: Primary conductors

Gas may also be included in the trench.

Take nothing for granted when excavating a joint usetrench for repairs. Never assume that a particularcable is your target. Always follow proper spiking tool procedures before cutting into any cable.

Unlike the duct and maintenance hole installation, thedirect buried system offers no protection from sharprocks and other debris that may come into contactwith the cable when the trench is being backfilled. Toavoid potential problems, a layer of bedding (sand,limestone screening, etc.) is required to protect thecable. NOTE: To ensure best protection, the layer of

bedding should be a minimum of 15 cm /6 inches around the entire cable.

The bedding has other benefits. It allows moisture topass through it to the bottom of the trench, awayfrom the cable and provides a visual indication tothose excavating that they might be in proximity to acable or trench.

Other methods to indicate proximity include buriedwarning tape and marker balls. (See Figure 4)

When installed above the bedding (before the originalsoil is used to backfill the rest of the trench) warningtape offers a visual indicator to those excavating that

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there is buried service inproximity. Marker ballsare also meant to beburied. They offer anadvantage as they canbe programmed. Thismeans their location andany information youchoose to include, can beretrieved with a locatingdevice.

303 CONDUIT INSTALLATIONInstalling underground cable in conduit generallyrequires two separate operations: a method ofinstalling a pull rope or line into the conduit, and theactual installation of the power or communicationscable into separate conduits. Each operation entails aspecific safe work practice. In both the roping andpulling operations, it is imperative that only appropri-ate equipment in good repair be used by competentpersonnel. Effective communication is essentialbetween workers at the rodding and pulling end andthe cable reel end.

304 CONDUIT ROPINGThere are two ways to install a rope or pull line: - manually or mechanically rodding the conduit- using compressed air

In either case, the rod or the rope should not contactany existing or adjacent conductors already in the maintenance chamber/vault. (Existing cables shouldbe moved and/or appropriately covered.)

Figure 4

305 MECHANICAL RODDINGMechanical rodders generally use a high strengthspring steel rod approximately 11 mm / 0.46 in. indiameter which is truck or trailer-mounted.Hydraulically-driven rollers push the rod through atemporary conduit guide set built from the under-ground conduit to the back of the rodder. The guideset must be securely connected to both the under-ground conduit and the rodder, and cannot contactany adjacent cables. Additionally, the rodder truck ortrailer should be properly grounded, and the operatorshould stand on a platform or a properly groundedmat.

Steel “fish” consist of flat, high-strength steel tape orrod that is manually pushed up the duct. Althoughstrong, they are heavy and electrically conductive. Toavoid incidents, workers should take care when liftingand lowering the fish into maintenancechambers/vaults and avoid contact with energizedequipment when the fish came out the duct at the farend.

Due to its lightweight and dielectric properties, thefibreglass duct rodder gradually replaced steel fish.Today’s duct rodder consists of a fibreglass core with

a plastic jacket (seeFigure 5) wound intoa dispensing storagereel equipped with abrake. NOTE: Never use abare fibreglass rod.If it breaks, thesharp end caninjure whoever ispushing the rod.

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Figure 5

Whenever the rod is fully retracted, pull the end outof the feeding eye, and insert it into the cage to pre-vent the rod from self-dispensing. Likewise, if the rod-der will be unattended while the end of the rod is inthe conduit, make sure the reel brake is engaged.This will prevent any remaining rod from self-dispens-ing.

306 PNEUMATIC RODDINGAn alternative methodis to use compressedair to blow the pullrope into the conduit.Two methods are available: low pressure/high volume(see Figure 6) andhigh pressure/low volume (see Figure 7).

Both utilize a missile to propel the lead end of therope through the duct.

The low pressure/high volume method typicallyinvolves a small handheld device with two to threefan motors (similar to a shop vacuum), operating atabout 3-5 psi at 300 cubic feet per minute air. Toavoid taking the electrical apparatus into a wet loca-tion, a 5 cm / 2 in. diameter hose is fed into the cable

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Figure 7

Figure 6

chamber. A tapered seal-off is held in the duct by atechnician while the rope is blown into the duct.

At this low pressure, a technician can safely remain inthe vault during the roping, as long as he/sheremains to one side of the duct and is wearing hear-ing protection and either safety glasses and/or a faceshield to protect against any debris or water that maybe expelled from the duct.

The high pressure/low volume method uses an air compressor that typically produces 100–125 psi at 90– 185 cubic feet per minute of air. They are gasolineor diesel powered and usually trailer or truck mount-ed.

An expanding device installed in the duct seals the airand allows free passage of the rope. These expandingring(s) can be rubber, similar to a duct plug, or a rub-ber bladder.NOTE: The duct plug style is generally rated for

only 10–15 psi air pressure.) No one should remain in the vault while the compressor is operating. Anyone looking into the vault should wear appropriate eye and hearing protection.

First, introduce compressed air into the duct andmake sure it exhausts out the duct at the reel end.This will prevent the creation of a pressure vessel inthe duct.

Winch manufacturers now offer winch line blower kitsthat operate as high pressure/low volume units capa-ble of blowing a steel winch line into the conduit asdescribed above. (See Figure 8)

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These units use a seal-off with a gripping system thatembeds in the duct and can withstand air pressure of60–100 psi. No one should remain in the cablechamber while these devices are operating.

NOTE: To determine the maximum pressure thatcould develop, multiply the duct diame-ter by Π (3.14) to find the area of the duct. Then multiply the duct area by the air pressure.

For a four-inch duct, this would be: 4 X 3.14 = 12.56 square inches x 100 psi= 1,256 psi of air in the duct.

If the duct is blocked, the seal-off and hose will even-tually exit the duct at high speed. This has the poten-tial to significantly damage equipment and/or severe-ly injure workers.

307 CABLE INSTALLATIONWinches typically consist of three designs: drum style,capstan and constant tension planetary style. (SeeFigures 9, 10, and 11)

In all styles, it is essential to ensure that the wire or synthetic rope is in good repair and free of any kinksor broken strands.

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Figure 8

Use an appropriateswivel to avoidintroducing torquefrom the twistedrope to the cable(see Figure 12).This torque candamage the cableand present a haz-ard when the ten-sion is released.

Pull a mandrelthrough the ductbefore installing thecable to make surethere is enoughclearance to avoidcable damage. Atrailing rope shouldfollow the mandrelin order to with-draw it if the ductis blocked.

Install appropriatehardware in thevaults or panels toensure that thepulling rope cannotrub against any-thing located near-by. Ideally, at thefeed end, the cable

should be totallyenclosed in the duct with a flexible cable guide or“elephant trunk” to provide mechanical protection

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Figure 9: drum winch

Figure 10: capstan winch

Figure 11: constant tension

and allow controlled application of a suitable cablelubricant to minimize pulling tensions. (See Figure 13)

At the pull end, sheaves ortravelers should be installed toavoid the winch line rubbingon the duct face, vault ceiling,or lid collar. Travelers shouldbe of sufficient diameter toavoid exceeding cable mini-mum bend radius.

Ideally, the winch shouldincorporate a tension displayand/or limiting device toavoid exceeding the rope lim-its and cable manufacturer’spulling tensions. The cableshould be installed slowly untilthe pulling eye or grip is up the duct to avoid anyhang-ups.

If the winch has no distance counter, consider wrap-ping phase tape or spraying locate paint on the winchline several metres ahead of the cable. When theoperator sees the tape or paint come out the duct atthe pull end, he/she can slow the pull down to easethe swivel/pulling eye/grip assembly out of the ductand around the travelers to the street. This avoidsshock loads that can damage the cable or strike per-sonnel.

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Figure 12

Figure 13

If the cable is not ordered with a pulling eye, technicians usually install a cable grip or sock on theend. (See Figure 14) The grip should be carefullyinspected for frays that can pierce safety gloves duringinstallation or removal. Grips should be installedaccording to manufacturers’ instructions. If a grip slipsoff at the wrong time, the end of the winch line canflail aboutfreely, pre-senting aconsiderablehazard topersonneland adja-cent equipment.

Pulling eyes are available that can be field-installedand that fasten onto the conductor, providing a highersafety factor. They are smooth, which reduces frictionin duct bends, and do not fray. In addition, cable manufacturers specify pulling on the conductor.

These pulling eyes consist of three components: asleeve nut with a tapered bore, a tapered plug (drivenor screwed into the centre of the conductor), and thepulling eye (screwed onto the sleeve nut over theplug). (See Figure 15) Make sure you use the correctsize and leave the proper amount of conductorexposed.

To avoid the eye pulling off under tension, make surethe plug is fully inserted into the conductor and cen-tred. When properly installed, the eye will be slightly

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Figure 15

Figure 14

loose on the conductor, but will seat once tension isapplied. Properly installed, the eye will withstand 200-300 per cent of the cable’s tension limit, or the cablewill break behind the eye.

The eyes are colour-coded by size. Once the cable isinstalled, the eye can be removed by cutting it off directly behind the sleeve nut, and stored until thenext use. Avoid taking the eye assembly apart andremoving the conductor pieces left inside, as they willkeep the tapered plug captive, ensuring that this com-ponent is not lost.

Crimp-on pullingeyes are alsoavailable. (SeeFigure 16) Theyare inserted ontothe end of thesingle conductor cableand crimped on with a tool that uses a wire rope tochoke the eye into the cable by distorting the conduc-tor/insulation. This is done three or four times alongthe length of the eye.

Follow the manufacturers’ instructions: the wire ropemust be embedded into the eye to a depth equal toits own diameter. Otherwise the pulling eye may pulloff under tension.

A similar crimp-on eye with a convoluted spike in thecentre is used onPILC three con-ductor cables.(See Figure 17)In this case aportion of the

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Figure 17

Figure 16

conductors are exposed before the eye is installed,and the conductors closest to the end are crimpedand distorted by the spike in three places. The eye isalso crimped in three places onto the lead jacket,making the eye assembly watertight. Again, thecrimper cable must be embedded into the pulling eyeto a depth equal to its own diameter to avoid failureunder tension.

Using either the reusable or the crimp-on eyes toinstall three separate single conductor cables requiresthe use of a pulling harness that staggers the cablesto avoid having all the cable ends in one place in theconduit. (See Figure 18) This lessens the chance thatthe cables will hang-up at a bend or joint in the duct.

The eyes are directly attached to each leg of the har-ness and a swivel of sufficient load rating is attachedto the sling link. If a large diameter synthetic pullingrope is used, a rope to swivel clevis can be usedbetween the swivel and the braided eye of the rope.

308 MAINTENANCE CHAMBER/VAULT HARDWARE

Various travelers or sheaves are available to insert in maintenance chambers/vaults to safely direct thewinch rope and the cable out of the conduit and upthe chimney toward the street. In most cases a sheave

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Figure 18

with two arms or yokes canbe lowered into the vault tothe proper height of the con-duit, then chained back to apulling eye or iron embeddedinto the wall. (See Figure 19)

Once tension is applied tothe winch rope, it is impor-tant to check that the winchline is still exiting the ductwithout rubbing on the wallof the vault. If necessary, thechain to the pulling iron mayhave to be shortened orlengthened to avoid contact.

If a pulling iron is not avail-able, or in the wrong location, a jamb skid can beused to mount the sheave.(See Figure 20) It consists ofa base section equipped witha foot on a rotating cam, andan upper extension thatslides into the top of the baseand pins into place. Theextension has a lip thatengages on the roof of thevault into the side of the chimney.

Once loosely installed, thecam can be actuated, which

raises the base section and jams the assembly inplace. A sheave or quadrant is then inserted into theassembly at the proper height so that the winch ropeand cable exit the duct without contact.

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Figure 20

Figure 19

The jamb skid is designed so thatthe more tension applied duringcable installation, the tighter thejamb skid locks into place. If theduct bank is not in the centre ofthe vault wall, the jamb skid canstill be used in conjunction with acable feeding sheave inserted inthe duct to direct the cable towardthe jamb skid. (See Figure 21)Figures 22 and 23 show otherexamples of chamber hardware.

If the winch truck cannot be posi-tioned directly over the vaultchimney, quadrant blocks or cor-ner cable guides can be installedon the lip of the cover ring todirect the winch rope and cableover the lip. This improves safetyby minimizing pulling tensions,and also minimizes dam-age to the cable sheath.Try to avoid spilling cablelubricant, as it creates aslip hazard.

309 INSTALLATION ON POLE

The place where theunderground systemtransfers to the overheadplant is referred to as a "riser" or "dip" pole. (SeeFigure 24)

The underground conductor can be terminated in oneof two ways. The most common is to apply the termi-

40

Figure 23

Figure 21

Figure 22

41

nation on the ground, theninstall the equipment on thepole. Alternatively, the cablemay be installed on the poleand the termination applied inthe air.

The method of termination youchoose depends on the size ofthe conductor, the type of ter-mination being applied, andthe proximity of other appara-tus. In either case, detailedinstructions for installationshould be followed to ensureproper operation and preventpremature aging.

Work on riser locations shouldbe in compliance with current regulations if energized con-ductors are in proximity.

It is important to support the cable as it runs the length of the pole. Any number ofdifferent methods (depending on the type of cablebeing used) are acceptable as long as they do notdamage the cable.

To complete the cable installation on the riser pole, provide protection by using steel/PVC cable guard orsteel/PVC piping.

310 CABLE TERMINATIONSFollow instructions exactly and use only approvedtools and equipment when installing these kits.

Figure 24

Improper installation starts the premature agingprocess of the cable and components. This is causedby moisture that is allowed to breach the cable andimproper control of stress that is present in an under-ground primary cable.

With all terminations, splices, and elbows, all of the layers of the underground primary cable must bestripped to the exact measurements and the compo-nents applied in accordance with the manufacturers’ specifications.

An underground primary cable will heat up and cooldown with the demands of the system. This cycling causes the cable to expand and contract and if thecable components are not installed properly, moisturecan be drawn into the component when the coolingcycle is contracting the cable. This contracting effectwill draw moisture into the cable if it has not beenproperly waterproofed.

Remember, adding a termination, splice, or elbow tothe cable creates a weak spot. Such installations mustbe constructed to specifications to maintain cablequality.

The four functions of a termination are:1. To offer a waterproof transition from the cable to

another component of the system2. To control stress3. To control tracking4. To conduct a nominal system current

1. TransitionAny transition should be waterproof to prevent mois-ture from entering the cable. (Follow the manufactur-er's instructions for a good quality termination.) Whenhand taping a termination, ensure the transition fromthe conductor lug is waterproofed using recommend-

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ed sealing tape.

Lug selection should fit the conductor size. Ensure theinstaller knows the size of the conductor and whetherit is solid, compressed, or standard round. All of theseconditions alter the physical size of the conductor andwill effect the operation of the lug connection. A looseor improperly compressed lug will create a high resistance connection that will, in turn, create heatand contribute to premature aging and failure.

2. Electrical Stress ControlElectrical stress can be controlled in two differentways. Stress created at the termination must be con-trolled where the insulation shield is cut back. This isdone using a stress ball that can be either hand tapedor pre-moulded.

The basic theory is that a stress ball adds insulation atthe point where the insulation shield is terminated.

The extra insulation at the stress ball allows for thelines of stress to find a ground reference at the insu-lation shield cut without breaking down the insulation.This is known as geometric stress control.

An alternate method of stress control is using coldshrink technology. Instead of a stress ball, whichrelieves stress at one point, this method uses a semi-conductive sleeve to redirect the lines of stressthroughout the termination. This is known as capaci-tive stress control.

Both technologies require that exact measurementsand installation procedures be adhered to, to ensureproper contact with the insulation shield and that theother layers are stepped properly so as not to inter-fere with the stress relief.

3. Tracking ControlWhen terminating a cable, there is full line voltage atone end of the termination (lug) and ground refer-ence at the other end. The distance between thesetwo points is called the tracking distance. To effective-ly control tracking, make sure that an adequate dis-tance exists between these two. (Remember that asvoltage levels increase, tracking distance increases.)

Rule of thumb for the tracking distance is 2.5 cm / 1inch per kV phase to phase. This will have to be determined and incorporated into the calculations forstripping when installing a hand taped termination.The kits will have voltage ratings on them and the instructions must be followed exactly.

To reduce the physical size of the termination, skirtsare added. These skirts add the required distance tocontrol tracking and reduce the overall length of the termination. Limits of approach should be maintainedto grounded structures and other voltages.

311 SPLICESSplices offer an opportunity to repair damage, con-nect old plant to new plant, or connect different sec-tions of new construction.

All splices, whether hot or cold kits or hand tapes,need to be waterproof to prevent moisture beingdrawn in during cycling of the cable under differentloads.

To maintain stress relief, waterproofing, and overallsafety, a splice should replace all layers of the cable (conductor, conductor shield, concentric neutrals, insulation, insulation shield, jacket).

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45

Pay particular attention to the following:Conductor: ensure the proper sleeve is used. Consider material: (copper, aluminum), size, type

(standard round, compressed, solid).

Concentric neutrals: ensure that all strands of the neutral are replaced and connected so as not to compro-mise the current carrying capaci-ty of the conductor. Always waterproof the splice when replacing the concentric neutral around the splice.

Jacket: After a splice, the jacket should continue to offer waterproofing properties and mechanical protection.

NOTE: Continuity of concentric neutral or cable shielding must be maintained by using an approved portable jumper prior to cutting or connecting those conductors.

312 INSTALLATION OF ELBOW CONNECTORSElbow connectors are designed and engineered for specific applications. It is therefore critical to followthe manufacturer's installation instructions. Whenselecting elbow connections consider insulation rating,conductor size, amperage rating, and loadbreak ver-sus non-potential elbow application.

Ensure the cable is trained into position before start-ing the installation. It must not interfere with other apparatus that may be in proximity to the elbow installation.

Consider how the elbow will operate once the systemis in operation. Ensure that there is enough slack toallow for elbow installation on an approved parkingstand or feed through.

Elbows and inserts are methods of transition betweenpieces of equipment. As with any component, followthe manufacturer's instructions. Unauthorized addi-tions/deletions to the installation of the elbows may compromise the integrity of the operation.

Elbows are an opportunity to switch the system. Theycan be switched under load and on potential if theyare designed to accommodate such operations.

The operator must positively identify the type of elbowbefore such operations are completed. Operating anon-loadbreak elbow while it is on potential or underload places the worker in immediate danger fromelbow failure and may damage the equipment

Again, waterproofing the connection is extremely important. If moisture is present when the cable iscycling, it can be drawn into the cable at the elbow connection if it not sealed properly.

Drain wires should be installed to maintain a bondbetween areas that are made of semi-conductive material. Typically there is a silicone seal that hasbeen added between these areas and the connectionbetween the semi-conductive elbow material and thesemi-conductive insulation shield is compromised. Toensure those two surfaces remain at the same groundpotential, the drain or bonding wires must be inplace.

The same applies for the insert/transformer connec-tion. Ensure the inserts are bonded to the groundinggrid in the transformer for the same reason.

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47

If these drains or bonds are not in place, trackingcaused from a difference in potential could damagethe equipment and put the worker at risk.

Remember, when the cable is manufactured, the conductor shield, insulation and insulation shield areextruded onto the conductor under extreme heat andpressure. When the cable is cooled, these layers areunder mechanical stress. When the cable is cut, themechanical stress is relieved, causing “shrink back”(the effect of the layers recessing).

That is one of the reasons that the manufacturer'sinstructions should be followed. The manufacturersfactor that shrink back into the cable design.

When selecting the manufacturer and the technologyfor terminations, splices, and/or elbows, ensure the equipment addresses these issues: waterproofing,stress control, tracking control, load make and break capabilities, custom tools that may be required, versatility for cable size.

The use of a utility knife to step back the different lay-ers of primary underground cable is not recommend-ed. Special tools are available to strip back encapsu-lated jacket, semi-conductive insulation shield, andinsulation. These tools ensure that the underlying lay-ers are not damaged during the installation of com-ponents.

Step the layers of the cable back to the manufactur-er's requirements so as not to compromise their tech-nology. The basic technology is the same across theindustry but each manufacturer will have specificrequirements for their products. Make sure to readand follow these requirements. Never apply one man-ufacturer’s procedures to another manufacturer’sproduct.

313 WORKING ON UNDERGROUND CABLE INSTALLATIONS

Once repairs to any cable system have ben complet-ed, check these items:

- Cable radius bends are gradual

- Duct boots or shoes are installed if removed or damaged

- Inspect permanent duct for damage

- Sharp objects aren't left in the trench to damage the cable

- Cables or splices are covered above and below with clean sand/fill NOTE: Do not use brick sand on high voltage

cables as it will capsulate primary cable. Limestone screening is pre-ferred.

- Document the required measurements of the splice/repair for future locating

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SECTION IVTRANSFORMERS AND SWITCHGEAR

400 General

401 Surge protection

402 Transformers

403 Switchgear

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SECTION IVTRANSFORMERS AND SWITCHGEAR

400 GENERALTransformers and switchgear are divided into two categories when referencing the method by which the primary cable is connected to the apparatus.

Live front identifies those connections that haveexposed components when in the normal operatingposition. Elbow connected equipment has no exposed components when in the normal operating position.

When operating live front or elbow connected apparatus, it is imperative that approved equipment isused to prevent flashover and undue mechanical orelectrical stress on the apparatus. The proximity ofgrounded cases to the energized apparatus can begreatly reduced depending on the type of equipment.

Steel pole encased transformers, live front equipmentand 28 kV rated elbow switches are examples of energized components in proximity to groundedcases.

Switchgear or transformers may or may not be suit-able to be used as switching and grounding locations.An elbow connection may not offer the appropriatelocation to install temporary parking stands to estab-lish open points or to perform grounding proceduresbefore removing any electrical apparatus.

Application of after market equipment may impedethe operation of an elbow switch.

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401 SURGE PROTECTIONWhenever an underground system is supplied from anoverhead system or vice versa, surge arresters shouldbe installed on the riser poles. Surge arresters shouldalso be considered at any normally open point in the underground system [for example, where doubling ofa voltage surge (e.g. lightning strike), may exceed theequipment’s basic insulation levels].

402 TRANSFORMERSTransformers are a location to step voltage up ordown. On an underground system, they can also beused as switching locations.

Figure 25 shows a live front transformer. It has liveexposed energized components in both the primarycompartment and secondary compartment.

These types of transformers have two cables in the primary compartment. One will be the feed and the

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Figure 25

other will continue to the next transformer andbecome the feed at the next location. The cables areconnected to arc-strangling switches and are appro-priate locations to switch the system.NOTE: Before opening this style of switch, make

sure the arc-strangler has been activat-ed. There should be no visible gap between it and the switch holder.

The top of the switches are connected to a bus barand there is a third switch that controls the feed tothe transformer location.

Always follow approved procedures and use only appropriate switching equipment due to the proximityof energized equipment to the grounded case.

Figure 26 shows an elbow-connected transformer. Aswith the live front padmount transformer, there aretwo cables that enter the vault. One will be the feedand the other will continue to the next location.

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Figure 26

Typical vault locations will have the elbows connectedto a three-point feed-through rack. The third positionis the cable that will connect to the transformer. As inthe minipad application, switching the system can beperformed at these locations. (These locations can beused as grounding locations for the system.)

In a submersible transformer application, the systemis an elbow connected application with no exposed energized components. Figure 27 shows a padmounttransformer. As with the submersible, it is an elbowconnected application.

These locations also offer switching and groundingcapabilities. There are exposed secondary bus bars.Depending on the type of transformer that is beingused, it can be outfitted with primary switches thatcan open the primary loop circuit inside, determinethe bushing that the transformer is to be fed from,and isolate the secondary bus bars at those locations.

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Figure 27

Figure 28 shows a three-phase padmount trans-former. These units can be outfitted to have differentfeatures. They can include a feed-through circuit forall three phases, primary switches to isolate the sec-ondary bus bars, and/or loop circuit switches.

403 SWITCHGEARSwitchgear allow the system to be switched and grounded. Depending on the type of apparatus, itcould be categorized as a live front or elbow connect-ed.

When operating gang operated switchgear, many ofthe same principles that are applied to operating an overhead air break switch can be applied.

A minimum of class 2 rubber gloves should be worn,appropriate personal protective equipment isrequired, and a portable ground gradient mat, con-nected to the system neutral to protect against steppotential hazards, should be used.

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Figure 28

When operating gang operated switches, as with anoverhead gang operated switch, it is important to perform the operation, check the operation of theswitch blades, and then lock the switch in the appro-priate position.

If Supervisory Control and Data Acquisition (SCADA)operated switches are being used for personal protection, the operation must be checked in accordance with the Utility Work Protection Code.

Figure 29 shows a fibregless switching cubicle with afour-point grounding rack for each phase that offers aswitching and grounding location.

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Figure 29

As there is limited space available to install groundingequipment, it is very important to have the cablestrained into position to allow elbow operation.

Figure 30 shows a three-phase switching cubicle.These units can be outfitted with a variety of switchingcapabilities.

Figure 31 shows a gang-operated solid blade switch.These units can also have a fused switch compartmentand may also be equipped to be operated remotelyby a SCADA system.

There are also multiple switching capabilities at a sin-gle location. It is very important that the system nomenclature accurately identifies the appropriateswitch.

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Figure 30

57

Figure 31

58

SECTION VSWITCHING AND GROUNDING

500 General

501 Equipment required

502 Tools

503 Switching

504 Tests

505 Temporary grounding

506 Cable testing

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SECTION VSWITCHING AND GROUNDING

500 GENERAL Switching on underground plant to establish work protection must be completed in compliance with theUtility Work Protection Code. Only after the work per-mit has been issued can grounds be applied to estab-lish a safe work zone.

The basic steps taken to de-energize a piece of equipment are as follows: - open- test- ground- lock and/or tag

501 EQUIPMENT REQUIREDFigure 32 illustrates the approved equipment requiredwhile conducting this type of work. Additional equipment may be required depending on the specifictype of application.

Workers should use the following (which shouldinclude but is not limited to):- FR clothing as required by Electrical Utility Safety

Rules- approved eye protection- hearing protection (as required)- minimum class 2 rubber gloves - approved hard hat

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502 TOOLSThe following tools are required:- live line tools; may include a grip all stick, switch

stick, or approved elbow puller using a weighted ram NOTE: The weighted ram should only be used

to pull the elbow and the normal phys-ical pressure from the worker to install the elbow to the new location.

- single, double and grounded parking stands- approved grounding leads with rated clamps and

elbows- if operation of a gang switch is part of the switch-

ing, a portable ground gradient mat should be used

- approved potential testing device

The following documentation is required:- OTO's (Order To Operate) as required by the Utility

Work Protection Code (UWPC)

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Figure 32

- tagging as required by the UWPC- documented tailboards- documented traffic plans as required- accurate maps and nomenclature

503 SWITCHINGAs with any switching that is performed on primary voltages, care should be taken to follow approved procedures. Unlike overhead plant, we are unable tovisually trace the conductor. Workers should rely onnomenclature, maps and approved procedures toensure safety while switching and grounding.

When switching is going to be performed, documen-tation must be completed in accordance with theUWPC and company policies.

Ensure that the equipment to be switched has been positively identified to match the OTO and maps.

A visual inspection of the switch and surroundingplant must be completed. This should include check-ing the condition of the switch for tracking, damage,signs of overheating, and, to ensure the switch can beoperated safely in an energized state (loadbreak) ifrequired by the OTO.

Along with the visual inspection, the use of high-techheat-sensing equipment (i.e. infrared guns) will assistthe worker to determine if excess heat is present therefore indicating a possible problem with theswitch.

Never operate any type of switch (elbow, fuse) usingonly your hands. No physical contact with the switchis permitted.

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Use extreme caution when operating elbow insulatingcaps that are rated above 15 kV due to the possibleflashover hazard that has been identified in the indus-try. If anti-flashover equipment can not be positively identified, other switching locations should be considered if the system allows (e.g. airbreak switch-es, gang-operated switches, oil switches etc.). If otherswitching locations are not an option, additional PPE(face shield, longer live line tools, high-rated FR clothing) should be used to protect against the flashhazard.

504 TESTSPotential tests are required before any portableground is placed on a piece of equipment. There aretwo methods to perform potential tests.

Method 1If the underground plant is equipped with a capacitivetest point, a potential indicator with capacitive testpoint capability can be used. It is imperative that the potential indicator have the capacitive test point capability, due to the false “no voltage” readings thatany other potential indicator will show.

Method 2If working on equipment that does not have a capaci-tive test point, a potential indicator should makedirect contact with the target. Making direct contactmight also be the method of choice even with acapacitive test point, due to possible false readingswith some types of test points.

In an elbow application, place the elbow on the dou-ble parking stand, and insert an approved potential indicator into the other parking stand insert.

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If the elbow is to be applied to a grounded parkingstand, the potential indicator should make contactwith the metal portion of the elbow pin to obtain anaccurate reading. An approved adapter that attachesto the potential indicator should be used.

Until the grounds are applied to a piece of equip-ment, it should be considered energized. All switchingand testing should be performed using approvedtools, PPE and approved procedures. Only after thegrounds have been installed can the work proceed.

505 TEMPORARY GROUNDINGBefore any apparatus can be considered de-ener-gized, grounds should be in place on the under-ground plant that is to be worked on.

Grounding equipment that is being used for personalprotection should be maintained and tested to ensurethat they provide the protection that is expected.

Determine the locations to apply grounds to createthe safe work zone in compliance with the UWPC. InURD work, those grounds are typically placed atexternal locations that lead to the work area.

If grounded parking stands are used to de-energizean elbow connected cable, approved procedures andequipment that ensure a potential check is performedshould be used before it is placed on the grounded parking stand.

Ensure that any grounding equipment is rated for thepossible fault currents that the system could be sub-ject to. All components including the clamps shouldbe inspected before use.

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In addition to grounding procedures that comply withthe UWPC, a procedure known as point-of-work grounding should be carried out when equipmentallows.

This is simply the application of grounds at the loca-tion that the work is to be performed. These are onlyused to verify the grounds that have been appliedaccording to the UWPC.

506 CABLE TESTINGTo identify defective equipment, to take plant out ofservice, or make repairs, the cable should first be test-ed. These tests vary but some add energy to the cableto verify the integrity of the manufacturing, installa-tion, damage, and/or repair.

Where testing will add energy to a cable or device,the test should be performed in strict compliance ofthe UWPC. Ensure tagging and work group notifica-tion has taken place.

It is imperative that each type of test equipment haveinstructions and the operator receive training on thespecific test equipment. This will help ensure properoperation, accurate results, and that the target equipment has proper status. It will also ensure safetyfor the operator, other workers and members of the public.

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66

SECTION VITROUBLESHOOTING

600 General

601 Initial communication

602 Current mapping

603 Types of systems

604 Types of faults

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SECTION VITROUBLESHOOTING

600 GENERALDuring any troubleshooting procedure, safe work methods should be adhered to at all times. Personal protective equipment, testing apparatus, and allapproved equipment should be used. Observation, constant communications and documentation are crit-ical elements for safe troubleshooting.

601 INITIAL COMMUNICATIONUpon receiving a trouble call order, document and confirm all the pertinent information from the receiv-er. Identify the correct mapping, tools, testing equip-ment, PPE, and vehicles needed. A tailboard docu-ment should be completed with the appropriate per-sonnel on site taking into account the type of systemand the type of fault.NOTE: Once the problem is identified, further

tailboard talks should be held to keep all sequences and personnel aware of work methods until power is restored.

602 CURRENT MAPPINGThe troubleshooting crew should be able to determinethe direction of the feed from the map, awareness ofopen points, correct phasing and be able to trace thecable route.

Maps should be current and verified with the control centre on any changes prior to commencement ofwork.

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All maps use symbols to denote certain apparatus,types of switches (with nomenclatures), number ofphases, voltages, and abnormal conditions such asout-of-phase status. Training to read and understandthese maps is important. NOTE: Constant communication with the control

centre should be maintained before tasks are performed to verify the mapinformation.

603 TYPES OF SYSTEMSTroubleshooters must recognize the type of under-ground system they are going to work on. These mayinclude:- all underground- mixed overhead and underground- a system fused with a breaker- a system employing fault indicators

604 TYPES OF FAULTSFaults can be permanent or transient. Awareness of abackfeed should be discussed, then the backfeed eliminated, before commencement of work.

1. Riser Poles:Complete a visual inspection at this location to identi-fy the condition of the following: - switches - ruptured fuse - arresters- leads and cable connections - cable guards - grounding attachments - burn marks - foreign objects or animals

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- terminations - overhead wire condition - damaged equipment on the road surface or lawns- evidence of tracking- ground fault indicators

2. Switch Gear/Load Centre Problems(a) Live Front

Inspect the exterior for condition of: - exterior of the unit- terminations- insulators and barriers - switches - fuses and fuse holders - condensation - contamination- ground fault indicators - cleaning, etc.

(b) Elbow Connected:Complete a visual inspection on the following items: - underground elbows and bonding leads, insulat-

ing caps- oil or gas leaks- visual open points- RFI (resettable fault interrupters)

3. Transformer ProblemsTest transformer using approved equipment

(a) Live Front: Conduct a visual inspection on: - terminations (heat, tracking) - insulators (cracks)- fuse and fuse holder (loadbreak style versus

straight fuse)- oil leaks

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- ground fault indicators

(b) Dead Front:Identify the condition of: - bayonet fuses (visual inspections and testing)- dry cannister fuses (visual inspections and test-

ing)- underground elbows and insulating caps- oil leaks- bushing inserts- arrester elbows- standoff or parked connectors- ground fault indicators

Test transformer with the approved equipment.

4. Primary Cable FaultsLocate the defective electrical apparatus.

Inspect fuses,breakers, termina-tions, elbows,arresters, etc.

Establish work per-mits, as required by UWPC.

Identify faultedsection of cableand pinpoint thefault.

Figures 33 through37 are examplesof various cableand fault-locatingequipment.

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Figure 33

The cable identification device shown in Figure 33positively identifies all three cables while they remaingrounded and there is no open end available.

Figure 34 shows adigital time domainreflectometer (TDR).It uses radar tolocate faults andwill automaticallyread the cable anddisplay the fault dis-tance with a singlethump.

Figure 35 shows ahandheld TDR. Itsends a string of suitable pulsesdown the cablewhich are wholly or partially reflected back from the

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Figure 34

Figure 35

fault. The size and shape of the pulses indicate thetype of fault.

Figure 36 shows a cable/pipe and fault locator knownas an A-frame.

Figure 37 is a phase identifier, designed to identify an isolated or de-energized cable within a group ofenergized cables. The location of the required splice isidentified by the direction and amplitude of the DCsignal coming from the transmitter.

Before excavation and repair:- acquire the appropriate locates- identify digging hazards, traffic hazards, etc. - ensure positive cable identification

Upon completion of the repair, all employees shouldreview the documented tailboard and communicate toensure a safe restoration of the apparatus.

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Figure 36

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Figure 37

SECTION VIICABLE AND FAULT LOCATING OF URD CABLES

700 Cable locating

701 Electro-magnetic induction

702 Signal frequency

703 Types of signals

704 Applying an active signal

705 Direct connection

706 Induction

707 Clamping the signal

708 Passive signals

709 Cable locating tips

710 Fault locating

711 Primary fault locating

712 Secondary fault locating

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SECTION VIICABLE AND FAULT LOCATING OF

UNDERGROUND CABLES

700 GENERALProvincial legislation requires utilities to provide accu-rate information on the exact location of their buriedplant whenever trenching or other construction workis being done in proximity to underground electricalplant. This information will reduce or eliminate dig-insand the potential for serious injury they present.

The following information will help you identify the underground magnetic fields which ultimately locatespecific buried plant. Personnel who perform this typeof work must be familiar with:- establishing a safe work area- the equipment and its operation as per the

manufacturers’ manuals, and- the importance of following safe work practices

701 ELECTRO-MAGNETIC INDUCTIONCable location devices do not actually locate thecable itself. Rather,they detect the magnet-ic field around the cable(or other buried plant)which is created by analternating current (AC)flowing along thecable/ plant along withan oscillating frequencyof reversals whichmakes this process suc-cessful. (See Figure 38)

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Figure 38

It works because it is not possible to insulate againsta magnetic field. The cylindrical shape of the inducedmagnetic field (known as a signal) is not changed bycable insulation or by the presence of different typesof soil.

To illustrate the principles of electromagnetic induc-tion, place a bar magnet into a coil of wire, then takea reading with a voltmeter. (See Figure 39) The volt-meter will show a deflection only while the magnet ismoving. As soon as the magnet stops, the instrumentreads zero.

If the magnet is withdrawn quickly, the meter deflec-tion will be in the opposite direction – but only until movement stops. The faster the magnet is moved, thehigher the reading.

The rate of change of an alternating voltage isreferred to as its frequency, which is the number ofpositive and negative pulsations (cycles) per second.Frequency is measured in Hertz (Hz). Just as movingthe magnet faster gives a higher reading, alternatinga field at a high frequency induces a higher voltagefor the same field strength.

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Figure 39

Volts

Instruments for locating buried cables use the princi-ples of electromagnetic induction in two ways:- to locate the AC signal on a cable with a receiver- for the transmitter to remotely apply a detectable

AC signal to a cable

For an electric circuit to be complete, current shouldbe allowed to flow. But how can a low powered signalsource at the surface make a detectable current flowin a properly insulated buried cable? The answer liesin the effect of capacitance on AC circuits.

Capacitance is the effect by which signals are able tojump across insulation. The surrounding soil acts as ifthere is a conducting layer around the conductor.

702 SIGNAL FREQUENCYOhm’s Law regarding signal frequency is essentiallythis:

The higher the signal frequency, the greater the AC voltage and signal induced in the conductor.

The higher the signal frequency, the greater the capacitance current flow.

Although high frequency signals are more effectivethan low frequency signals, they also flow to groundmore easily and therefore will not carry as far as low frequency signals of identical strength. Another drawback is that high frequency signals couples farmore readily that low frequency signals by mutualinduction to other cables in the vicinity.

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703 TYPES OF SIGNALSAn active signal is produced by a signal transmitterand applied to a cable so that it can be located andtraced with a receiver. The signal transmitter can alsoflood an area with signal so the cables in the areacan be found.

Passive signals occur naturally on cables as an effectof 50/60 Hz electric power or very low frequencyradio energy.

The best signal to locate and trace a line is an activesignal which has been deliberately applied for the purpose of locating and tracing.

704 APPLYING AN ACTIVE SIGNALAn active signal can be introduced by one of the following methods:- direct connection - induction- inductive coupler

705 DIRECT CONNECTIONThe output AC volt-age from the signaltransmitter is con-nected directly tothe cable at anaccess point suchas the end of theconductor. (SeeFigure 40) The cir-cuit is then com-pleted by connect-

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Figure 40

ing the transmitter to a stake or other ground point.

706 INDUCTIONThe aerial in a signal transmitter fed with an AC volt-age sets up a magnetic field through the coil returning through the earth below it.

As shown in Figure41, the transmitteraerial lies parallel toline AB and its fieldlinks around the lineon which the signalis induced. There isno linkage and nosignal induced online CD at rightangles to the aerial.

Laying the coil hori-zontal (as shown inFigure 42) producesa much less localizedfield spread. This isuseful for blanketsignal application,but the signal is not induced to a linedirectly below thecoil.

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Figure 41

Figure 42

707 CLAMPING THE SIGNALClamping uses the induction principle to give a resultsimilar to direct connection but without electrical con-tact to the cable. The output from the signal transmit-ter is applied to a target line by clamping around itwith a split, doughnut-shaped magnetic core,often referred to as aninductive coupler, whichcarries a primary windingmagnetizing the core withthe AC signal. (See Figure43) The line becomes thesecondary of a transformer,and will carry a strong sig-nal, provided that it is ade-quately grounded on eachend.

708 PASSIVE SIGNALSPassive signals are naturally present on most buriedcables. Current flowing in a cable produces a mag-netic field or passive signal, but a live cable with noload may not produce a signal strong enough to bedetectable.

However, power transmission systems induce straycurrents into the ground and form ground currentsstrong enough to enable most (not all) power cablesto be located passively. (See Figure 44)

709 CABLE LOCATING TIPS1. Identify and verify what you should locate (hydro,

CATV telephone, etc.).

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Figure 43

2. Choose the best method of applying the trace signal to the cable (direct connection, coupler, or induction with transmitter).

3. Choose the lowest frequency on your locator that puts out the best signal for that cable.

4. Locate in peak mode and confirm in null mode. Take a depth reading for your own information.

5. Ensure that all maps/prints and information concerning this locate have been visually checked and confirmed.

6. Always mark 4-9 m (15-30 ft.) more than the area requested.

7. Paint dots indicating peak location then, when returning, extend the dots into lines of direction in the work area.

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Figure 44

710 FAULT LOCATING

GeneralA cable fault may be defined as a conductor or insulation failure, potential leak, or short circuitbetween the conductor and the sheath, adjacent con-ductors, and/or ground.

The degree of accuracy in locating the fault willdepend on the type of fault, type of cable, the sur-rounding medium, the type of equipment and the skillof the operator.

Fault Locating Precautions:Fault locating procedures and/or equipment involvepossible exposure to high voltages. Take appropriate precautions to protect the public and personnel.

1. All cables should be properly identified and de-energized before any fault locating work begins.

2. The lock to lock rubber glove rule should be followed where cubicles, kiosks, padmount transformers etc. are involved.

3. If employees should enter any confined space (e.g. cable pit or underground vault) they must follow and complete the legislated requirements.

4. Proper work area protection should be estab-lished.

5. High voltage test equipment should be placed on a ground gradient mat. One employee should remain with this test equipment.

6. Before making any connections, the operator should complete a potential test on the cable to be tested, to ensure that it has been de-ener-gized.

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7. The cable should be disconnected at both ends. If necessary, work area protection should be established at each end.

8. Since high voltages and lethal currents could be involved, appropriately rated rubber gloves and proper personal protective equipment should be used when cables are being tested.

9. Before testing begins, the operator should ensure that all equipment is properly positioned, all connections are correct and all grounds are installed. Only now can the grounds on the cable be removed.

10. After the fault location is complete, the cable should be grounded to remove any capacitive charges that it may have retained. Tags shouldremain in place and the cables should remain grounded until the fault has been repaired.

Do’s & Don’ts:

- don’t over test voltage of rated cable (for 5 kV, stay under 10 kV DCfor 28 kV, stay under 56 kV DC)

- do a hi-pot test (reference cable section)

- do 100 kV DC – on 28 kV – new cable

- don’t exceed manufacturer’s recommendations on elbows and cables

711 PRIMARY FAULT LOCATINGThe best method to locate a cable fault is to thumpthe cable using a thumper with arc reflection coupledto a Time Domain Reflectometer (TDR). One or twothumps should register the fault on the TDR and showthe distance to the fault.

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Spiking procedure1. After the faulted cable has been located and

excavated, it is important to follow approved spik-ing procedures before cutting into the target.

2. The appropriate class of rubber gloves and approved personal protective equipment should be worn at all times during the spiking operation.

Preparing the spiking tool1. Connect one end of a portable ground to the

spiking tool and the other end to an approved ground (e.g. grounding grid, system neutral, tem-porary ground probe).

2. Holding the tool down toward the ground, look down the barrel to make sure it is clear of any foreign debris.

3. Load the tool with a spike and the appropriate shell. The shell size will depend on manufacturers requirements based on the type of cable insula-tion, the size of the conductor, and the concentric neutral.

4. Lay the shell firing pin activator rope out to its fulllength.

5. Install the spiking tool on the target cable, cock the firing pin, and clear the area.

Firing the spiking tool

1. Pull the rope from outside the excavation until theshot discharges.

2. Inspect the spike to ensure penetration of the cable.

3. Remove the spiking tool and proceed with the work.

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NOTE: Use only spiking tools that have been approved for use on multi-phase cable. These tools effectively referenceall the conductors to ground potential for positive identification.

712 SECONDARY FAULT LOCATING

1. Trace the entire cable route and mark it with the appropriate paint.

2. Determine what kind of fault you have (e.g. one leg to ground, a neutral burned open, a short between a hot leg and a neutral, etc.).

3. Isolate all three conductors at both ends.

4. Determine if the conductors are directly buried in the ground, or in conduit.

5. If you have a TDR, look at the various conductors to see if you can see the fault.

6. If the secondary service is directly buried, use an A-frame cable locator to pinpoint the fault from each end. NOTE: Always keep the portable reference

ground rod behind the start of the cable path 2-3 m (6-10 ft.) back.

7. If buried in corrugated high density polyethylene pipe or PVC conduit, use an A-frame cable locatorin case the pipe/duct is also damaged at the faultlocation. If there is no reversal in signal, try send-ing an 8 kHz signal to ground and retrace the route looking for a drop off at each end.

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METRIC/IMPERIAL CONVERSIONSLINEAR MEASURE

1 centimetre 0.39 inch1 inch 2.54 centimetres1 foot 0.30 metre1 metre (3 feet 3 inches) 1.09 yards1 yard 0.91 metre1 rod 5.02 metres1 kilometre 0.62 mile1 mile 1.60 kilometres

SQUARE MEASURE1 square centimetre 0.15 square inch1 square inch 6.45 square centimetres1 square foot 0.09 square metre1 square metre 1.19 square yards1 square yard 0.83 square metre1 hectare 2.47 acres1 acre 0.40 hectare1 square kilometre 0.38 square mile1 square mile 2.59 square kilometres

WEIGHTS1 gram 0.03 ounce1 ounce 28.35 grams1 kilogram 2.20 pounds1 pound 0.45 kilogram1 metric ton 0.98 English ton1 English ton 1.01 metric tons

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MARINERS' MEASURE6 feet 1 fathom120 fathoms 1 cable length5,280 feet 1 statute mile6,076.11 feet 1 nautical mile

SQUARE MEASURE144 square inches 1 square foot9 square feet 1 square yard30 1/4 square yards 1 square rod640 acres 1 square mile

MEASURE OF VOLUME1 cubic centimetre 0.06 cubic inch1 cubic inch 16.39 cubic centimetres1 cubic foot 0.02 cubic metre1 cubic metre 1.30 cubic yards1 cubic yard 0.76 cubic metre1 litre 1.05 quarts liquid1 quart dry 1.1 litres1 quart liquid 0.94 litre1 gallon 3.78 litres1 peck 8.81 litres1 hectoliter 2.83 bushels

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TEMPERATURE CONVERSIONSA Fahrenheit degree is lesser than a Celsius(Centigrade) degree, one Fahrenheit degree being5/9 of a Celsius degree.To convert Fahrenheit degrees into Celsius, subtract32, multiply by 5, and divide by 9.To convert Celsius into Fahrenheit, multiply by 9,divide by 5, and add 32.The freezing point of water is 32º F. (0º C). The boil-ing point is 212º F. (100º C).

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© Copyright 2011. All Rights ReservedInfrastructure Health & Safety Association

SPG12

• Bare Hand Live Line Techniques

• Conductor Stringing• Entry and Work in a

Confi ned Space• Excavating with

Hydrovacs in the Vicinity of Underground Electrical Plant

• High Voltage Rubber Techniques up to 36 kV

• Hydraulics

• Ladder Safety • Line Clearing Operations• Live Line Tool Techniques • Low Voltage Applications • Pole Handling• Ropes, Rigging and

Slinging Hardware• Temporary Grounding

and Bonding Techniques• Underground Electrical

Systems

Available Safe Practice Guides