Grounding and Jumpering

7/30/2019 Grounding and Jumpering

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Groundingand

Jumpering


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Table of Contents

Chapter I

Pages Subject2 - 9 Engineering and Theoretical Study

Chapter II

Pages Subject10 - 13 Protective Procedures


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CHAPTER I

GROUNDING AND JUMPERINGKEY TO SAFE WORK ON DE-ENERGIZED SYSTEMS

INTRODUCTIONTemporary grounding has received much attention fromthe application hardware and practice points of view.

This chapter will deal with the subject primarily from

the engineering and theoretical points of view. Not withthe purpose of getting involved in deep drawn out formu-

lations, but to show the basic theories which give soundfoundations for proper grounding and jumpering prac-

tices.

Two major points will be emphasized throughout thischapter. First is the use of the terms grounding and

jumpering as opposed to the classic terminology lim-ited to grounding. Importance of the term jumpering

will become more evident as you will see. Second is theemphasis on safety. Background, theory, details andapplication of safe grounding and jumpering will be a

theme throughout this chapter. The information pre-sented is equally applicable to distribution, transmis-

sion and substation work.

WHY IS TEMPORARY GROUNDINGSO IMPORTANT?This question has been asked and answered many timesso we will only review the highlights. Definitely we want

to keep safety of the work area as our prime requisite. Onsystems which are de-energized, many occurrences must

be considered for continuous safety of the workman.

Induced voltage from adjacent energized lines is a con-stant consideration. Even though the system which is

being worked has been de-energized there is electromagnetic feedover from adjacent systems which areenergized. These may be systems on the same structure

or on adjacent structures. The magnitude of feedoverwill vary with the proximity of the adjacent systems and

with the magnitude of current on those systems. Majorconcern for this feedover is that it is of a continuous

nature due to the continuous current flow on the adja-cent systems. Therefore, induced voltages must begrounded to avoid possible electrical injury, discomfort

and inadvertent reaction of the workman.

Fault currents on adjacent systems introduce a marked

increase in the magnitude of feedover on the de-ener-gized lines. While these fault currents will probably be

of short duration, their magnitudes are such that the de-energized work area must be properly grounded and

jumpered to avoid considerable danger to the work crew.

Although the de-energized work area may be bathed inbright sunlight, a storm on some other portion of the

system could result in lightning striking the de-ener-gized system and giving rise to transients which wouldrender the work area extremely unsafe unless properly

grounded and jumpered.

Another major consideration is accidental energizing of

the system. Workmen will undoubtedly make certainthat the system is de-energized before starting work, but

through carelessness or misunderstanding, switchesmay be closed and energize the system in the work area.

Accidents on adjacent systems, at crossovers or on over-builds, could result in energized lines coming in contact

with the de-energized system.

These situations all call for adequate grounding andjumpering procedures to ensure that a safe work area ismaintained.

We have covered many of the known general factorswhich give rise to the need for safe grounding and

jumpering; factors that support our contention that your

grounding and jumpering practices should be given athorough review.

Our electrical oriented world has increased the use of

electrical power enormously during the past few years.As a result, increased generator capacities have beenintroduced. Along with this growth there have been

marked increases in substation capacities, all of whichmeans more power available in the case of mistake orfault with corresponding increases in resultant danger

in the work area.

Increased congestion of current carrying systems due toincreased system complexities and the need for better

use of space and materials have given rise to consider-ably more system feedover. The increased number, size

and complexity of substations are manifestations of

these system growths. Increased numbers of conductorsper structure have come about through the need forbetter utilization of each structure. Increased numbersof conductors per right-of-way are a necessity due to the

need for better use of available land. These develop-ments have brought increasing numbers of energized

systems in close proximity with the de-energized lineand have brought increased feedover probabilities.

Increases in currents carried on systems are evidenced

by the increased conductor sizes and the increased use ofbundled conductors. With these increased currents ac-companying increases in feedover must be considered.

HOW GROUNDING AND JUMPERINGHAS DEVELOPEDTo appreciate the present grounding and jumperingpractices and to see what considerations should be

foremost in reviewing and upgrading these practices, wemust look at grounding and jumpering progress over the

years. Many papers have covered the practice of throw-ing a chain over the line or how tap clamps with No. 6

wire were used for grounding, so we will start a bitfarther down the development path. The accompanyingsketches will give some basics in the development of

grounding and jumpering practices which apply to trans-mission, substation and distribution systems.


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Figure 1 portrays the classic practice of connecting eachconductor to a driven ground by means of quite long

cables. This incorporates two points of interest which wewill pursue in depth throughout our discussion. Onepoint is the emphasis on cable length. The other is the

location of cable connections in the work area. At firstglance the workman on this structure may seem safe by

grounding practices of this nature. To evaluate theworkmans safety we will examine in detail just what the

electrical situation actually is.

The electrical equivalent of this structure is shown in

Figure 2. Rj is the resistance of the jumper cable, Rm isthe resistance of the workman and Rg is the groundresistance of the structure area. The important point of

this circuit is that during current flow conditions Rj andRgare in series and this combination of resistance is in

parallel with Rm.

Fig. 1

ELECTRICAL EQUIVALENT

The combined value of Rj and Rgwill vary considerablyfrom one work site to another. For purposes of this

discussion a rather low combined value of 1 ohm will beconsidered. The value of Rm has been the subject of many

papers and discussions. The combination of body resis-tance and contact resistance of a palm to conductor

condition typical of a work position may be in the orderof 5000 ohms but for purposes of this discussion a rather

Fig. 2

widely accepted body resistance value of 500 ohms wilbe considered.

If a current of 1000 amperes is encountered in the de-

energized system, the voltage drop across Rj and Rgwilbe the product of 1,000 amperes times 1 ohm or 1,000

volts. I think we can all agree that the 1,000 ampere

current is quite conservative on todays systems. The1,000 volt drop is thus correspondingly conservative

This voltage drop of 1,000 volts is impressed across Rm

the workman, and results in a current flow through himof 1,000 volts divided by 500 ohms or 2 amperes. As wecan readily see, there is a rather severe problem even

with the conservative current flow of amperes on thegrounded de-energized system. Much of this problemis caused by the excessive voltage drop incurred as a

result of Rg.

A natural step toward improving grounding practiceswas to connect all three grounding cables to a common

driven ground connection as shown in Figure 3. Thisreduced the Rg between phases so that the phase-to-

phase resistance was virtually eliminated. This resulted

in faster system reaction to clear the faulted line, however the practice still left the ground resistance in

parallel with the work area and thus did not reduce thevoltage drop across the workman.

Fig. 3

A further step along this line of thinking was to run the

cables close together for ease of handling as diagramedin Figure 4. The electromagnetic forces involved during

fault currents on these closely located cables resulted inexplosive results and discouraged further pursuit of this

convenience.

In an attempt to achieve work convenience while mini

mizing cable length and cable resistance between phasesthe practice of jumpering directly from phase-to-phase

was instituted as shown in Figure 5. This reduced thenumber of lengthy leads to ground, reduced the violent

action of multiple down leads during fault currents andachieved a minimum resistance between phases for

rapid clearing of system faults. The method still utilizeda single lead from one of the phases to a driven groundand thus left a high ground resistance and high voltage

drop across the work area.

A natural evolution toward reducing the voltage dropacross the work area is to run the down lead to the


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common ground of the structure. Further reduction of

the voltage drop in the down lead is accomplished byshortening the lead length and connecting it to thestructure just below the work area as shown in Figure 6.

This practice gives short jumper lengths between phasesto keep the resistance at a minimum. When a man is

jumpered in this position, he is in parallel with a mini-mum of resistance and is subjected to a minimum volt-

age drop in case of current flow in the system. Whenthere is a system neutral, a cable should also be con-nected to it for complete jumpering protection and to

ensure lowest resistance in the ground return to thesource.

The electrical equivalent of this system shown in Figure

7 readily discloses the advantages of having the manjumpered by only a cable resistance. This resistance

could be in the order of 1 milliohm. The situation has nowchanged resistance and resultant voltage drop across

the work area by a factor of 103, bringing a one voltimpressed potential across the work area. This drasticreduction in voltage drop across the work area forms the

basis for jumpering as a key to safe work practices. Themarkedly lower voltages also reduce likelihood of skin

puncture and thus permit use of man-to-conductor resis-tances of considerably greater values than body resis-

tance alone.

Fig. 4

Fig. 5

Fig. 6

Fig. 7

ELECTRICAL EQUIVALENT

To further appreciate the importance of keeping the

jumper resistance at a minimum, we should look at theseries of components which are in parallel with the workarea. The detailed electrical equivalent of the jumper

resistance is shown in Figure 8. These resistances con-sist of the surface contact resistance between the clamp

and the conductor, the resistance of the clamp itself, theresistance of the jumper cable, the resistance of the other

clamp, and the resistance of the surface contact betweenthe clamp and the structure. At the A. B. Chance Re-search Center, we have conducted extensive studies and

tests relative to the factors which make up these resis-tances.

These factors combined with other items which should

be thought of in optimizing the grounding and jumperingsystem are summarized in five major considerations.

Item No. 1 is Choose adequate capacity clamps. This

means choosing clamps for adequate mechanical size tofit the conductor (cable or bus). It also means choosing

clamps which have adequate electrical capacity to with-stand the maximum realizable system current for thefull time duration over which that current may be

encountered. Some examples of clamps with their par-ticular mechanical and electrical capacities are shown in

Figures 9 through 11. In addition to physical size and


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current rating, the clamp shown in Figure 11 offers

another feature worthy of attention. It has the ability toswivel so that it can be connected readily in difficultareas such as on the conductor at the end of a string of

deadend insulators.

Item No. 2 is Choose adequate capacity cables. Threemajor considerations should be kept in mind when

choosing the cable. One, the terminal capacity must beadequate. The terminals used on Chance grounding

cables are designed and tested to ensure good mechani-cal and electrical interfaces between the cable and the

clamp. The terminals are designed for strong, low resis-tance connection with the clamp by matching the termi-nal interface to the clamp. The design of machined

ferrules provides intimate and solid mechanical andelectrical crimping characteristics so that the cable is

captivated to withstand the severe mechanical forces ofshort circuit current and to provide minimum voltage

drop in the cable circuit.

The second consideration in choosing the cable is cable

size. The electrical system characteristics which areused in choosing the proper size are magnitude on thegreatest realizable current on the system and time

duration of that current. The cable chosen must not fuseduring this service since a fused jumper cable has a

rather high resistance and resultant high voltage drop.

Figure 12 shows fusing curves for various sizes of copperconductors as a function of current and time in cycles at60 hertz. The maximum realizable system current canbe located along the abscissa which is given in amperes

times 1000. The number of cycles for which the cable willbe subjected to the maximum system current is located

on the right hand ordinate given in cycles at 60 hertz. Asan example, a system with a maximum fault current of

20,000 amperes for 30 cycles duration would have anintersection near the 1/0 cable curve. To ensure against

cable fusing during fault conditions a cable above the1/0 size would be chosen.

Fig. 8

DETAILEDELECTRICALEQUIVALENT

OFJUMPER

Fig. 9

C600-0337MECHANICAL CAPACITY

MAIN LINE TAP

(2) 4/0 StraightStud Terminal

MAX.6.62O.D

MIN.4.50O.D

Fig. 9-1

ELECTRICAL CAPACITY

Rated Current Capacity Outdoors with 4/0 Copper Tap

CONTINUOUSCURRENT550 AMPS

15 CYCLES40,000 AMPS

FAULT CURRENT


Fig. 10


MAIN LINE TAP

2 to 4/0 GroundTerminal

MAX.1.162O.D

MIN..162O.D

Fig. 10-1

ELECTRICAL CAPACITY




FAULT CURRENT



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Fig. 11

G4228-10SJMECHANICAL CAPACITY

MAIN LINE TAP

2 to 4/0 GroundCable

MAX.2.88O.D

MIN..258O.D

Fig. 11-1

ELECTRICAL CAPACITY




FAULT CURRENT


Fig. 12

The third consideration in choosing the cable is to relatethe maximum system current, and the jumper resis-

tance so that the voltage drop across the work area isensured of being at a safe level. The work site willgenerally dictate jumper length. From the jumper length

and the voltage drop which will be safely tolerable acrossthe work site it then becomes necessary to choose a cable

size offering low enough resistance. In some instancesthis may entail use of parallel jumpers to ensure that

under maximum system currents the work area voltagedrop is sufficiently low.

Item 3 is Clean connections. The surface to which a

clamp connects is generally corroded, contaminated orin the case of structure connections possibly even insu-lated by paint. This high resistance surface will add

significant voltage drop to the jumper circuit. To get thesurface clean and ensure a low voltage drop, the conduc-

tor should be wire brushed. Some structure surfacesmay have to be filled and brushed before clamps are

applied. From an operating standpoint it would be desir-able to accomplish the cleaning without a separatebrushing operation. At the A. B. Chance Research Cen-

ter we have conducted extensive testing with clampsapplied to contaminated conductors. While we are firm

advocates of cleaning conductors prior to applying clamps,we have established that the serrated jaws of ground

clamps such as pictured in Figure 13 do serve to pen-etrate surface corrosion and provide a satisfactory lowresistance contact between the clamp and the conductor

when a separate cleaning operation is impractical. Theclamp should be lightly tightened in place, given a slight

rotation on the conductor to allow cleaning action by theserrated jaws and the clamp should then be securely

tightened in place.

In addition to the serrated jaws for aid in removingcorrosion during clamp installation the flat face clampshown in Figure 14 provides an extra margin of corro-

sion penetration. This is accomplished by means of acone pointed setscrew. After the clamp has been lightly

tightened, rotated and then securely tightened on thebus or tower structure, the setscrew is tightened to

ensure penetration of any remaining surface contami-nation.

Item 4 is Locate Clamps for Jumpering. The key tomaintaining a safe work area is to keep the voltage drop

across it at a minimum. The jumpering diagram shownin Figure 15 and its electrical equivalent shown inFigure 16 point out the key factors of phase-to-phase

jumpering combined with jumpers connected to thesystem neutral and to the structure at a point immedi-

ately below the work area.

Item 5 is Minimize cable slack. An obvious consider-ation is that shorter cables offer low resistance. However

and of greater importance is the fact that tremendousforces are involved during fault currents. These forcesresult in severe and dangerous cable movements in the

case of excessive cable slack. Words cannot begin toexpress the importance of proper cable routing to avoid


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MAIN LINEMAX. MIN.1.5 0.125

O.D.. O.D.

TAP

2 TO 4/0Ground Cable



FAULT CURRENT15 CYCLES 30 CYCLES

43,000 AMPS 30,000 AMPS

Fig. 14-1

Fig. 13


MAIN LINE TAP

(2) 4/0 THREADStud Terminal

MAX.3.00O.D

MIN..50O.D

Fig. 13-1

ELECTRICAL CAPACITY




FAULT CURRENT


ELECTRICAL CAPACITY

Fig. 15

Fig. 16

excessive slack. A film including high speed movie foot

age taken during grounding and jumpering tests at theA. B. Chance Research Center vividly portrays the

importance of minimizing cable slack as well as severalother aspects of grounding and jumpering discussed in

this chapter. Films (No. 25 and 52) are obtainable onloan from the Chance Advertising Department.

Therefore, this list of five major considerations is the

basis for safe grounding and jumpering.1. Choose adequate capacity clamps

2. Choose adequate capacity cable3. Clean connections4. Locate clamps for jumpering

5. Minimize cable slack

These are indeed the keys to safe work on de-energizedsystems.

Fig. 14


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Selecting ground clamps and cable

To serve your particular needs, the Chance grounding line comprises both ready-made sets and separate components for yourspecifications. Among the options and criteria to consider:

Coordinated connectors Terminal (either pressure-typeor threaded-type) selected for clamps dictates the cable-ferruletype (either plain or threaded) to match.

Functional fit Sizes of the clamp types in Chance ToolCatalog Section 3000, Grounding Equipment, appear in as-cending order of maximum-main-line size. By design, manyclamps serve a wide range for their conductor type (cable, busor tower).

Adequate capacity Published ratings for both clamps

and cable must withstand maximum-potential system fault-current magnitude and full-time duration. Certified test re-ports are available on request.

On-site handling Application clearances and fit (for over-

head conductors and ground wires, transmission tower shapes,URD apparatus or substation buswork) affect clamp and cabledimensions.

How to order a Grounding Set

In addition to the specifying criteria above, each part of agrounding set requires certain choices:

1. ClampsASTM designations for Type, Class and Grade for clampsshown in Chance Tool Catalog Section 3000.

2. FerrulesCopper or aluminum. Plain or threaded.

3. CableLength required to reach application distances.ASTM Type I with black or yellow elastomer jackets fortemperatures from -40F (-40C) through +94F (+90C).ASTM Type III with clear thermoplastic jacket for tempera-tures from +14F (-10C) through +140F (+60C) should beused only in well-ventilated areas.

4. Support StudThis option recommended on only one clamp to help controllifting the set to the first clamp attachment point.

5. Shrink TubingThis translucent option recommended for stress relief andinspection of cable strands between ferrule and jacket.

4. Support Stud

5. Shrink Tubing

3. Cable

1. Clamps

2. Ferrules

Substation grounding special considerations

As the ratio of inductive reactance to resistance (XL/R) increases near and in substations, so also do fault currents become moreasymmetrical. This increases heating and mechanical forces to levels beyond requirements for on-line applications. For thesesevere applications, special attention must be given to grounding-clamp selection. Working toward additional guidance in thisregard are ASTM and IEEE. For a typical substation with an XL/R of 14 the IEC (International Electro-Technical Commission)grounding standard for this application Chance has successfully tested at 43,000 amperes for 15 cycles these clamp catalognumbers: G3367-2, G4229-1SJ, C600-1743, C600-0065, C600-1733, C600-1783, T600-0658 and C600-0337. For specifics on eachclamp, see Chance Tool Catalog Section 3000.

Grounding Set Ratings

ContinuousCurrent

Rating, ARMS,60 Hz

200250300350400450

550

MinimumCable Size

with FerruleInstalledEqual or

Larger Than

#21/02/03/04/0

250 kcmilor two 2/0350 kcmil

or two 4/0

A Withstand and ultimate short circuit properties are based on performance with surges not exceeding 20%asymmetry factor (see Appendices X3 and X4, ASTM F 855).

B Ultimate rating represents a symmetrical current which the clamp shall carry for the specified time.

Reference:

Derived from ASTM F 855,Standard Specifications for TemporaryProtective Grounds to be Used on De-energized Electric Power Lines andEquipment

15cycles(250MS)

142127344354

74

Copper CableSize

#21/02/03/04/0

250 kcmil ortwo 2/0

350 kcmil or

two 4/0

30cycles(500MS)

101520253039

54

Withstand Rating,Symmetrical kA RMS, 60 Hz

Ultimate Rating/Capacity,B

Symmetrical kA RMS, 60 Hz

Short Circuit PropertiesA

6cycles(100MS)

2948617696

114

159

15cycles(250MS)

183038486072

101

30cycles(500MS)

132127344351

71

60cycles(1 S)

91519243036

50


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CHAPTER II

PROTECTIVE GROUNDING FOR LINE PERSONNELThe three basic method of protecting linemen are to:

(1) Insulate the energized conductors and other ener-gized parts.

(2) Isolate all energized conductors and energized partsfrom the work area.

(3) De-energize and place protective grounds on eachside of the work area.

For Number (1), rubber and plastic cover equipmentshould be used through the distribution voltages desig-nated as safe for the insulation method.

For Number (2), hot line tools should be used to detachand remove from their insulated supports, on the struc-tures, the energized parts, thus isolating the work areaby moving all energized parts beyond reach.

The third method is the one to be discussed today de-energized lines by forces of nature, failure of parts,

vandalism or a planned outage. Regardless of how the

line becomes de-energized, a routine procedure has to befollowed before the linemen can work safely. Remember,if you cant see both ends, its hot. If it isnt grounded,it isnt dead.

Since we cant see both ends, we have to get word fromthe load dispatcher or dispatchers at each end of the lineto be sure there is no chance for possible back feed andthat all switches have been opened and hold tags placedon them. The hold tags will be assigned to the supervisorin charge of the work and can only be removed when thatsupervisor, whose name is on the hold tag, calls in andreports all work completed, all grounds removed and allmen in the clear.

On lower voltage lines coming from unattended stations,a troubleman or member of the line crew is told whatcircuit is to be de-energized by opening the recloser bynumber and the air break switch by number and placingthe hold tag on the air break switch handle or on the lock.

In no case should anyone consider automatic switchingdevices, such as oil reclosers, as a switching clearance tode-energize the line for safety. On rural lines, if there isno visible air break on the circuit, the leads from therecloser to the section of line to be worked should beremoved. Precautions will have to taken in removing thefirst two leads if there is an ungrounded transformerbank beyond the reclosers. The first two leads could behot and provisions should be made to keep them away

from men and any part of the structure until the last oneis removed from the recloser.

With all the above, there is no guarantee to the linementhat the line is de-energized and safe to contact. Al-though infrequent, the wrong switches could have beenopened through bad communications or human error.Today, two-way radios have eliminated some of thecommunication problems. There is also the possibility ofaccidental contact with an adjacent line or on crossovers.

A car striking a pole or weather conditions have causedmany accidental contacts. All of these possibilities makegrounding absolutely necessary.

In 1954 Messrs. Harrington and Martin with BoonevillePower Administration made tests to determine safeworking conditions for linemen should the line they wereon be accidentally energized. This information is con-tained in an A.I.E.E. Paper No. 54-206, dated July 9

1954. They found the accepted rule, by most companiesof installing protective grounds on adjacent towers to theone being worked on, would not provide adequate protec-tion should the lineman contact the tower or conductorsduring accidental energization of the line. They alsodetermined that short circuiting and grounding all conductors at the work location, using leads and clamps ofadequate current carrying capacity, would provide suf-ficient protection for the linemen. Their report causedmany companies to reevaluate their grounding equip-ment and grounding practices. Many utilities made acomplete study of their fault currents and found theirequipment and practices to be inadequate to protect thelinemen should the line be accidentally energized.

Their study revealed the size conductors used in groundleads were in some cases too large. Such excessivelylarge size conductors were unnecessarily costly and theextra weight made the equipment difficult to use. Insome cases, the diameter of leads were too small as faultcurrents were continually going up. They also foundtheir clamps didnt have adequate current carryingcapacity. In many instances, hot line clamps were beingused instead of ground clamps. Hot line clamps werenever designed and tested for ratings for continuouscurrent and fault currents at 15 and 30 cycles. Since theBooneville test in 1954, Chance has joined forces withseveral operating companies conducting extensive studyand test programs on grounding equipment in our labo-

ratory. Some of the equipment tested was on the operating utilities line trucks, including weathered and corroded wire of various sizes, which was removed fromservice. Ground clamps in some cases were attached toa piece of corroded conductor. These burned the conductor in two at 3 to 5 cycles and 10,000 amps. After theconductor received minor cleaning, the same equipmenwithstood in excess of 11,000 amps for 25 cycles, whichis required for a safe operation.

In over 200 field and laboratory tests in a joint programbetween Philadelphia Electric Company and Chancesix ground clamps were developed with replaceableserrated jaw inserts that clean both the ground and

conductor during attachment. The serrations on thealuminum alloy inserts bite through enough of thecorrosion to make a safe connection during normalclamp installation. Where the attachment is on a heavilycorroded area, rotating or moving the clamp as it istightened causes a scrubbing action that cleans awaycorrosion, making a low resistance contact.

With the high forces set up on short circuits, the clampscable and cable attachments must provide adequatemechanical strength. Periodic inspection for brokenstrands that can weaken the grounding leads, electrically and mechanically, is very important.


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Fig. 1

Fig. 2

After the Philadelphia Electric Chance groundingtests, Chance conducted other tests with other utilitieson heavy distribution and subtransmission circuits todetermine what would be needed in the way of cablesizes, clamps and ferrules to handle these higher faultconditions and provide protection to their line person-nel. Along with these tests, different types of groundingprocedures were studied to find safe and easier workingmethods.

Violent action on long leads on high current tests indi-

cated that phase-to-phase jumpers would be the bestmethod of reducing the violent action of ground leadscoming down the pole in the linemans working area.

When grounding on distribution systems, the commonneutral or system ground should be considered for theground end of one or more ground leads.

For ungrounded systems, a screw or driven ground rodshould be employed to establish ground and a leadcoming up the pole and attaching to a metal bracket orground support below the work area should be used.

After the cable support has been grounded at ground,one cable lead or jumper should run from the groundsupport, attached to the pole, to one phase using thatphase as the ground source for the jumpers for the othertwo phases.

The best procedure found for single pole distribution andsubtransmission is to ground from the ground bracketon the pole to one of the outside phases. Then a jumperfrom the grounded outside phase to the middle phaseand the third jumper from the middle phase to the otheroutside phase.

In some single pole structures it may be advisable toground the two bottom phases through the metal bracketon the pole, then one of the bottom phases to the middleor top phase. This would be particularly true on two-armconstruction.

Where shield wires are used, it is also a good idea to bondor jumper the nearest phase with another jumper fromthe shield wire to one of the bonded phases. The leadsshould be kept as short as possible and, in many caseswhere longer leads are used, they can be pushed fartheraway from the pole to shorten them and to get them outof the workmans way.

Some utilities have adopted what we believe to be thesafest grounding procedure for transmission. Theyground all three phases at each end of the area. Thismight involve several crews on a major job or perhapsseveral structures to be worked by a single crew. Inaddition to placing a ground at each end of the work area,

they also require what may be considered a personalground for the phase the crew is working on. This notonly gives the lineman better protection, but also as-sures him that no mistake has been made in de-energiz-ing the line when the personal ground is placed adjacentto the work area.

On ungrounded distribution circuits andsubtransmission, guy wires should also be bonded togrounded phases. The safest position for a lineman on apole where shield wires are available is to establish aground below his feet and also a ground from the shieldwire down to the grounded conductor.

Figure 1 shows a typical 69 kV 3-phase installationwhere the ground bar is placed below the linemans feetwith a jumper being installed from a screw ground rod tothe grounding bar. The second ground jumper is placedfrom the grounding bar to the outside phase. The third

jumper is installed from the bottom phase to the topphase. If a static wire is attached to the pole, this shouldbe tied into one of the phase wires.

A typical jumpering operation is shown on Figures 2 and3 which are probably the most popular structures andconsist of 3 phases and a neutral wire. You will note inall cases that we stress that the grounding bar be placed


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Fig. 3

Fig. 5

Fig. 4

below the linemans feet to keep him and the structureat the same potential.

This procedure calls for a jumper connected from thegrounding bar to the neutral bar with a jumper runningfrom the bar to the screw ground rod. A jumper is thenplaced from the grounding bar to the middle conductorwith phase-to-phase grounding techniques used fromthis point.

Figure 4 Grounding of Steel Poles. When jumperingconductors on steel poles, certain attachments are nec-essary for adequate grounding. This can be accom-plished three ways:

a. Weld a nut on the pole for installation of a ground lugshown in Figure 4. When this nut is not in use, a plasticcap should be inserted in the nut to keep moisture andcontamination out. Before inserting lug, make sure thatthe lug is clean and also that the threads on the nutwelded to the pole are clean. A non-oxide should be

placed on the threads of the nut and stud for a goodelectrical connection.

b. A small angle can be welded to the pole which wilserve the same purpose as the lug.

c. A portable grounding bar can be placed on the polewith a screw tightener. The most important point inusing this bar is that the two set screws located one oneach side of the grounded bar be tightened so that the setscrew point will penetrate the galvanizing or paint toinsure a good electrical connection.

We realize that by tightening down on this set screw, itwill damage the galvanizing or paint, but a suitableprimer or paint can be applied to the damaged area toprevent rust. The most important thing is to have a goodelectrical connection to protect the lineman working onthe structure.

You will note that the same jumpering procedure is usedas Figure 1 except that the jumper going from the groundbar to the screw ground rod was eliminated. The pole isbeing used to replace this jumper.

Figure 5 The H fixture is one of the most commonstructures on voltages from 69 kV through 345 kV single

and bundle conductor. Install a grounding bar below thelinemans feet, jumper from grounding bar to screwground rod. If there is a pole ground on the pole, jumperthis ground to the grounding bar. Step No. 1 Jumperfrom the grounding bar to the middle phase. No. 2 Jumper from the middle phase to one of the outsidephases. No. 3 Jumper from the middle phase to theother outside phase. No. 4 If there is static wire on thepole, jumper from the static to the middle phase. No. 5 In the case where there are two linemen required on thestructure, a ground bar should be placed below thesecond linemans feet and a jumper placed from the barto the middle conductor.

Where you have long phase spacing, it may be difficultfor one lineman to control the jumper leads, however, byusing two linemen and tying a handline in the middle othe jumper to control the weight, the lineman willexperience little difficulty in making the recommended


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Fig. 5A

Fig. 6

Fig. 7

ground connections. In cases where there is bundleconductor, it is recommended that each conductor of thebundle be grounded.

GROUNDING ON STEEL TOWERS

Safety rules vary from utility to utility. Some companiesallow their linemen to ground directly over the conduc-tor while some require that they ground from below the

conductor as shown in Figure 6.

One method for grounding directly over the conductorwhere bundle conductors are used is shown in Figure 7 (grounding bar) using a single jumper attached to thetower and the middle of the grounding bar. This bar canbe lowered into position with a handline or a gripallclamp-stick. After the grounding bar is positioned sothat the clamps seat on the conductor, the eye screws canbe tightened, thus giving a good jumpering attachmentto the bundle conductor.

In the case where you cannot ground directly above the

conductor, the handline can be placed approximately inthe middle of the crossarm overhead. The tower end ofthe jumper should be attached firmly to the tower legbelow the linemans feet and the handline attached tothe stick used to put the ground on the conductor end. Byattaching the handline to the grounding stick, the line-man does not have to lift the weight of the jumper, butcan guide the ground clamp onto the conductor andtighten it securely. It is recommended that all conduc-tors of the bundle be jumpered. This can be accomplishedby running separate leads from the tower to the bundleconductor or using a short jumper, grounding eachconductor in the bundle.

We recommend phase-to-phase jumpering but with thelarger phase spacing, it may seem quite difficult. Inwhich case, the crossarm could be considered the phase-to-phase ground. However, serious consideration shouldbe given regarding ground resistance between the con-nection points.

We have conducted tests on corten steel and found that

with all the various connection points and the resistancebuilt up in the corten at the connection points, anadequate ground is not obtainable. A separate jumpermust be run down the tower and tied into the counterposeand static wire, if not insulated, to obtain a good groundconnection.


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Fig. 9

C600-1625Chisel Set

T600-1922Spiked Clamp

T600-2233

For underground cables, penetrator ground sets areavailable wih chisel- and spike-point clamps. See Figure9.

Chisel-point clamp main-line capacity is 112". C-Typeclamp in Chisel Sets fits conductors from #6 (0.162") to636 kcmil ACSR (0.998").

Spike-point clamp main-line capacity is 212". C-typeclamp in Spike Set fits conductors from #6 (0.162") to 2"O.D. bus.

Each set includes 6-ft. of #2 copper clear-jacket groundcable and ferrules, a penetrator clamp (choice of hardened-steel 12"-wide chisel or conical spike) and C-typegrounding clamp.

Screw-type copper-clad ground rod in sets indicated is24" long for easy handling. The helix (spiral), handle andwing nut are bronze.

Chisel Set with Ground Rod

For restricted-space applications and as a truck-ground-ing system, a compact ball and socket clamp designdelivers a high-current rating usually associated withonly large clamps. See Figure 8.

It applies to a wide range of switching equipment,including:

Industrial metalclad gear,Substations indoors and out,Distribution overhead and underground.

For trucks, a ball stud permanently mounts on eachbody.

Two clamp styles and two ball-stud lengths adapt tomany applications. Clamp bodies, eyescrews and ball-studs are bronze alloy. Tin-plated ball-studs have nomi-nal 1"-diameter ball and stud to fit NEMA terminalpads. Lockwasher and nut are silicone bronze.

ASTM Designation of Type I, Class A, Grade 5.

Fig. 8


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Fig. 10

SUMMARY

(1) Linemens protective grounds are one of the mostimportant parts of any line construction tool kit.

(2) Clamps should be selected with adequate continu-ous current carrying capacity, short circuit carryingcapacity and mechanical strength.

(3) Cable and cable attachments to the ground clampsshould have adequate current carrying capacity andmechanical strength.

(4) Install grounds as close to the work area as ispossible. On transmission voltages, in addition togrounding all three phases at each end of the workarea, a personal ground should be used at the worklocation on the phase being worked on.

Fig. 11

A rotating ground tool is mounted on the arbor shaftadjacent to the reel of conductor. A ground conductoris installed in the non-rotating collar connector and toa suitable ground provision. The inner end of the reelconductor is then inserted into the ground connectorlocated on the rotating flange. As the reel is turned,electrical ground continuity is assured. See Figure 11.

The GR-27BS2 has been tested to 27 kA faultcurrent level (2/0 Rating).

The GR-43BS2 has been tested to 43 kA faultlevel (4/0 Rating).

Tested per ASTM F855 Standard.

GR-27BS2

GR-43BS2

CatalogNumber

GR-27BS2(27 kA Rating)

GR-43BS2(43 kA Rating)

Max. PipeDia. (D)

21116"

ConnectorType

Two1"-diameterBall Studs

ConnectorRange

See Ball StudClamp on

Chance Cat.page 3013 inTool Catalog.

Traveling grounds are required when stringing conduc-tors in close proximity to energized conductors. Therehave been many accidents reported where conductorshave inadvertently contacted an energized conductorcausing serious injury. Also, the traveling ground willbleed off any static buildup due to inductance fromenergized conductors. See Figure 10.

A traveling ground is required on all conductors beingstrung. The jumper lead going from the traveling groundshould be attached to the system neutral. The traveling

ground should also be jumpered to the stringing orbreaking rig.

When removing conductors from the stringing blocks forclipping in, the conductors should be adequately groundedbefore removal from the stringing sheave. Do not dependon the conductive liner on the sheave wheel as this linerdoes pick up residue from the conductor.

(5) Phase-to-phase jumpering after one phase has beengrounded is the best protection should the linebecome energized.

(6) Never place a ground clamp over armor rod.

(7) Maintain the same working distance from an un-grounded conductor as you would an energized con-ductor until it is grounded.

(8) Check for potential before grounding.

(9) If it isnt grounded, it isnt dead.


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NOTE: Because Hubbell has a policy of continuous product improvement, we reserve the right to change design and specifications without notice.2004 Hubbell Printed in USA

B lletin 09 8002 R 6/2004 RGS 10M

UNITED STATES

HUBBELL POWER SYSTEMS, INC.

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Centralia, Mo 65240-1395

Phone: 573-682-5521

Fax: 573-682-8714

e-mail: [email protected]

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HUBBELL CANADA, INC.

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Phone: 905-839-1138

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Fax: 65-6454-4775e-mail: [email protected]

Web: http://www.hubbellpowersystems.comE-mail: [email protected]

Grounding and Jumpering

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