Cable Ladder Bonding with Earth Wire, Is it Necessary?

TPMJH-201001

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Abstract — In Western Australian mining sites there is a

practice of bonding cable ladder sections with an earth wire,

instead of relying totally on the splice plates for earthing. A

common requirement today is the provision of earthing

conductors linking cold formed cable ladder sections. There is a

lack of information relating as to the relevance of this

requirement or where this practice has originated. This paper

reports on testing carried out on actual cable ladder, and

examines the effect of adding an earthing conductor to achieve a

continuous low resistance earth path between the cable ladder

sections. From an examination of the results, assessment is made

of the effectiveness of the bonding conductor, followed by

discussion of the risks involved with and without earth wires, and

the merits of discontinuing or continuing the practice.

Index Terms — Bonding, Earth Wire, Jumper, Cable Ladder,

Cable Tray, Earthing.

I. INTRODUCTION

OR the majority of installations, especially in process and

crushing plants in mining industries, there is a large

quantity of cable ladder installed, where it is used primarily for

supporting electric cables. The cable ladder generally used is

metal, and as such is considered a wiring enclosure which may

become live, requiring grounding. Earthing of the cable ladder

is important and is also a requirement of The Wiring Rules,

AS 3000. Electrical grounding is essential for both personnel

safety and to ensure protection systems operate correctly to

remove power from a faulted cable. However the wiring

standards do not stipulate that cable ladder sections be bonded

by earthing wires across each joint, merely that the ladder

itself be bonded to the main earthing system.

There appears to be mixed opinions and engineering

knowledge as to the practice of installing bonding wires, or to

its relevance in the installation of cable ladder systems.

This paper investigates the effectiveness of the current

Manuscript received April 1, 2010. (Current version published April 1,

2010.) This work was supported in part by Kounis Metal Industries Perth

WA. Paper no. TPMJH201001.

Michael J Hamilton is with Elinco Engineering Services, Perth WA; PO

Box 510 Balcatta WA 6914, Tel: 0418 277 177, e-mail:

[email protected].

File Number: TPMJH-201001.

practice of using bonding wires across joined sections of cable

ladder for providing a continuous earth path, and the merit of

providing earth wires as an improvement to reducing the

resistance across a splice plate section of the cable ladder

system. The risk will also be investigated where an earth

bonding wire is not used to form part of the earthing system.

II. BACKGROUND

The current practice as seen from experience of many cable

ladder installations is the prolific use of bonding wires. Figure

1, shows an example of such a typical installation in a mining

environment that has earth bonding wires between all cable

ladder sections. Figure 2 showing a close up of the cable

ladder. Generally only one earth bonding wire is installed to

the ladder, which is to the outside face of the ladder system as

the inside rail would not easily be visible or accessible.

Fig. 1. Typical photograph of installed cable ladder showing separate earth

bonding cables.

In an effort to find out where this practice may have

developed from, questions that have been asked of electrical

personnel on various sites offered no resolution. Some people,

a minority, believe the earth bonding wire is not required,

whereas the vast majority believe it is required. Commonly

electrical supervisors on site would not approve the installation

and would not allow power to be applied until all cable ladder

bonding wires had been installed to all splice joints of cable

ladder.

Cable Ladder Bonding with Earth Wire,

Is it Necessary?

Michael J Hamilton, Member IEAust.

F

TPMJH-201001

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Fig. 2. Close up of installed cable ladder showing earth bonding cables.

One manufacturer of cable ladder systems in Western

Australia, through requests from users and installers of such

cable ladder, also supplies bonding wires, firstly only with

16mm2 cable and later more so with 25mm

2 cable, and a

special bonding wire bolt hole for such bonding wires.

Previously bonding wires had commonly been bolted to one of

the splice plate bolts prior to these specific bonding wire bolt

holes being available.

Generally the final inspection and sign off on an installation

is in the hands of the site electrical supervisor, whom will

often call for bonding wires to be installed to cable ladder

splice sections at all joints. When asked as to their reasoning

behind such an instruction the answer is often because it is

specified, or because it provides a sense of security. No

reference to sound engineering theory or practice was cited.

This paper investigates some theoretical analysis and

various tests on the cable ladder circuit to review the effect on

resistance with and without the use of bonding wires.

Assessment is also carried out on the risks that may present,

such as failure of bolts or failure to tighten splice plate bolts

during construction, if there is no bonding earth wire present.

III. THEORETICAL ANALYSIS

A. System Components / Component Values

For the theoretical analysis, the following assumptions are

used for calculations. To determine the resistance of the

ladder, the steel has been taken as iron with a resistivity of

9.71 x 10-8

m, compared with copper that has a resistivity of

1.72 x 10-8

m, copper being 5.65 times better than iron.

Note that the area offered by the ladder rail is 272mm2 for

1.6mm and 340mm2 for 2.0mm, where the 1.6mm rail offers

more than 10 times the area compared with 25mm2 copper

cables.

The resistance values of 1 meter lengths of ladder and 1

metre lengths of cable are given as:

16mm2 Copper Cable – 1.15 x 10

-3

25mm2 Copper Cable – 7.27 x 10

-4

Ladder Rail (1.6mm x 130mm) – 0.357 x 10-4

Ladder Rail (2.0mm x 130mm) – 0.285 x 10-4

The change from using 1.6mm ladder to 2.0mm ladder gives

a reduction in resistance by 20%. Similarly a change from

using 16mm2 bonding wire to 25mm

2 gives a reduction in

resistance by 37%. For the analysis only 1.6mm type ladder is

considered as this would represent the most commonly used

type of cable ladder, and also give the least improved results.

For simplicity the galvanised coating of the steel has been

ignored.

Figure 3 shows the splice plate arrangement of two typical

joined cable ladder sections in detail. There are slotted holes

in the splice plate which allow for expansion of the ladder.

Generally expansion is allowed for by leaving a 20mm space

from each end of the cable ladder sections, and with all the

splice plate bolts tightened the ladder will still provide

movement during expansion and contraction.

Fig. 3. Picture of cable ladder sections joined with spice plate showing the

earth bonding wire connected.

The equivalent circuit of the splice section between the

joining of two sections of cable ladder is shown in figure 4.

This circuit model is used to determine the Thevenin

equivalent resistance between the points A and B, which is at

the locations where the bonding wire connects to the ladder.

The following naming representation is used:

R.wire – the bonding wire resistance.

R.rung – the resistance of the rung section

between the two side rails.

R.rail – the resistance of the side rail sections.

R.sp – the resistance of the splice plate

sections.

R.gap – the resistance across the 20mm gap

between the two ladder sections,

relying on the splice plate only.

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Fig. 4. Equivalent circuit of two joined cable ladder sections.

The resistor ‘R.wire’ between points A and B is the

resistance of a connected bonding wire, whose length is

typically 600mm to reach between the two bonding points on

each section of ladder. Figure 5 shows the resultant circuit.

Fig. 5. Resultant circuit of cable ladder and bonding wire.

‘R.ladder’ represents the Thevenin equivalent resistance of

the series parallel combinations of the cable ladder and splice

plates. The simplified circuit however does not fully show the

parallel effects of the remaining lengths of ladder.

Due to the splice plate having a similar construction to the

ladder side rail the resistance of the end sections is effectively

halved by the paralleling of both the rail and splice plate.

Providing a good low resistance connection is made between

the splice plate and rail section, the bonding wire in effect is

trying to improve on the resistance offered by the splice joint

gap.

B. Theoretical Findings

From figure 5 the equivalent resistance across the points A

and B, R.ladder is determined by calculation to be 88 µ.

After adding a bonding wire across the points the effective

resistance becomes:

With 16mm2 cable – 78 µ, and

With 25mm2 cable – 73 µ.

To determine the improvement of adding the bonding wires

formula (1) is used to calculate this, where A represents the

resistance without bonding wire and B the resistance with a

bonding wire attached.

%1

100tImprovemen%

A

BA (1)

The percentage improvement, taken as the decrease in

resistance across the points for the addition of each cable size

is then:

With 16mm2 cable – 11.3%, and

With 25mm2 cable – 16.8%.

A summary of the theoretical values for various widths of

cable ladder are given in Table I.

TABLE I

THEORETICAL RESISTANCE VALUES FOR VARIOUS SIZES OF CABLE LADDER

WITH AND WITHOUT BONDING WIRE.

Ladder

Width

Resistance b/w

Points A and B

(µ)

Resistance b/w

Points A and B With

Earth Bonding Wire

(µ)

PERCENT

IMPROVEMENT

(%)

With 16mm2 bonding wire

600 88 78 11.33

300 85 76 11.01

150 81 72 10.51

With 25mm2 bonding wire

600 88 73 16.82

300 85 71 16.36

150 81 68 15.69

From Table I it is seen that the percentage increase is only a

small value, which is not providing for much of an

improvement. The decrease in resistance with 16mm2 cable is

only 10 µ. Note though that the analysis is performed at

close proximity to the splice plate section where the effect is

greatest with regards to the improvement in reducing the splice

section resistance. Another important point to consider is the

end-to-end resistance of the cable ladder system in determining

the net benefit of adding a bonding wire, discussed further in

section V.

However these figures for the ladder are based on assumed

values of the resistivity of the cable ladder and that all joints

are perfect with no additional resistances, hence to obtain more

meaningful results it is required for actual test data to be

explored and analysed.

IV. TESTING OF CABLE LADDER

A. General

There are various types of cable ladder in use which are

generally constructed of steel and hot dip galvanised. For the

Kounis cable ladder the galvanising is a coating of zinc at 390

gm/m2, approximately a thickness of 55µm. These cable

ladder types include:

TPMJH-201001

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3/50 (NEMA 16A), 1.6mm thickness, 100mm high rails

4/70L (NEMA 20B), 1.6mm thickness, 130mm high rails

4/70 (NEMA 20B), 2.0mm thickness, 130mm high rails

5/112 (NEMA 20C), 2.0mm thickness, 146mmm high rails

The most common cable ladder used in mining sites is the

heavy duty type NEMA 20B. The NEMA 20B to Australian

rated ladder represents the Kounis 4/70L using 1.6mm steel

thickness and 4/70 uses 2mm steel thickness, where the 2mm

type ladder is being used predominantly in cyclone prone

areas. For the tests the 1.6mm steel ladder 4/70L will be used

for determining the effect of the bonding wire, as this will be

more common than with the 2mm ladder construction. Also

the 2mm ladder will give improved results over the 1.6mm

ladder tests.

The purpose of the testing is to determine the reduction in

resistance across the splice joint with the addition of the earth

bonding wire, and to determine if the bonding wire provides an

advantage in various scenarios.

B. Method of Testing

The measurement points for the tests have been taken at 1

meter distance from each end of the ladder sections with a gap

between the two ladder sections of 20mm as would be

maintained in an installation to allow for expansion. The

measurement points therefore are 2.02m apart.

The removal of bolts is performed by removing the outer

bolts and working in a clockwise direction on the left side and

an anticlockwise direction on the right side. Bolts are

removed from the front and rear splice plate. Where ‘a bolt is

removed’, it refers to one front and one rear bolt being

removed. Where ‘bolts are removed from one side’ this refers

to the right side section only, both from the front and back.

The various tests are performed with finger tight and torque

tight bolts. The torque for tight bolts is maintained at 28Nm,

the nominal torque value for 10mm bolts. For the finger tight

bolts, the bolts were screwed to a point where the nut and

washer made contact with the ladder, just nipped up by the

unassisted fingers of one hand.

Each set of the tests were performed without a bonding wire

attached, and then with the bonding wire attached. Where the

bonding wire is attached, the bolts securing the bonding wire

are always tightened with a toque wrench.

The tests have been carried out using a Megger digital low

resistance meter (Ductor tester) with the measuring current set

at 10Amps, giving a range of 1.999m and an accuracy of

±0.2%, ±0.2µ.

The tests have been carried out on short lengths of ladder,

only 2 meters long. The effect this will have on the results will

be to raise the resistance values slightly as paralleling effects

of the ladder are reduced due to the remaining 4 meters of

ladder not being present.

C. Test Results

Tables II and III give the test results from the series of tests

carried out on 600mm wide cable ladder, and Tables IV and V

for 300mm wide ladder. Where tests include an earth bonding

wire, the size of the cable is 16mm2.

TABLE II

RESISTANCE TEST RESULTS FOR 600MM WIDE LADDER

WITH FINGER TIGHT BOLTS.

Bolts

Finger

Tight

Resistance Without

Earth Bonding Wire

(µ)

Resistance With

Earth Bonding

Wire (µ)

Percentage

Improvement

Bolts In Splice Plate - 1 Side Only

4 601.2 532.6 11.41%

3 598.1 534.5 10.63%

2 606.1 536.7 11.45%

1 515.7 540.7 -4.85%

Bolts In Splice Plate – 2 Sides

4 573.3 537.7 6.21%

3 606.9 552.7 8.93%

2 630.5 560.7 11.07%

1 662.7 603.9 8.87%

TABLE III


WITH TIGHTENED BOLTS.

Bolts

Tight

Resistance Without

Earth Bonding Wire

(µ)

Resistance With

Earth Bonding

Wire (µ)

Percentage

Improvement


4 481.0 472.8 1.70%

3 483.2 474.8 1.74%

2 489.9 480.8 1.86%

1 496.4 485.5 2.20%

Bolts In Splice Plate - 2 Sides

4 482.0 472.3 2.01%

3 485.5 475.5 2.06%

2 497.4 485.7 2.35%

1 515.8 500.9 2.89%

Table VI shows the results of tests conducted with the full

set of bolts in the splice plates and comparing the use of

16mm2 bonding wire with 25mm

2.

Table VII gives results to further tests on independent

sections of ladder and earth bonding wire. Due to the

complexity, theoretical values for 1 and 2 meter sections of

ladder have not been determined.

TPMJH-201001

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TABLE IV


WITH FINGER TIGHT BOLTS.

Bolts

Finger

Tight

Resistance Without

Earth Bonding Wire

(µ)

Resistance With

Earth Bonding

Wire (µ)

Percentage

Improvement


4 534.1 510.4 4.44%

3 537.8 511.1 4.96%

2 544.6 515.3 5.38%

1 543.1 511.9 5.74%


4 530.0 504.2 4.87%

3 549.6 512.1 6.82%

2 582.3 525.0 9.84%

1 610.1 542.8 11.03%

TABLE V


WITH TIGHTENED BOLTS.

Bolts

Tight

Resistance Without

Earth Bonding Wire

(µ)

Resistance With

Earth Bonding

Wire (µ)

Percentage

Improvement


4 453.4 446.0 1.63%

3 456.1 447.6 1.86%

2 462.7 454.0 1.88%

1 469.4 458.5 2.32%


4 453.4 446.0 1.63%

3 457.4 449.8 1.66%

2 470.5 461.8 1.85%

1 484.1 471.4 2.62%

TABLE VI

MISCELLANEOUS TESTS FOR SECTIONS OF LADDER.

Test

Measured

Resistance with

16mm2 Bond wire

(µ)

Measured

Resistance with

25mm2 Bond wire

(µ)

Percentage

Improvement

600mm,

Finger

Tight Bolts

524.9 537.7 2.44%

600mm,

Tight Bolts

472.8 469.6 0.67%

300mm,

Tight Bolts

448.3 445.2 0.69%

TABLE VII

COMPARISONS BETWEEN THEORETICAL AND MEASURED RESISTANCE VALUES

FOR SECTIONS OF 600MM WIDE LADDER AND EARTH WIRE.

Test Theoretical

Resistance (µ)

Measured

Resistance (µ)

Percentage

Error

Splice Plate 230.6 216.8 5.98%

600W Ladder

(1m)

Not Determined 354.4

600W Ladder

(2m)


300W Ladder

(1m)


300W Ladder

(2m)


16mm2 Earth

Wire

736.0 699.5 4.96%

25mm2 Earth

Wire

461.6 476.0 3.12%

D. Summary of Results

The results show that between 300mm ladder and 600mm

wide ladder, the percentage improvements with the bonding

wire attached are similar and as such further comparisons will

refer only to 600mm ladder as this is the most common type

used. The 300mm wide ladder tests give better results due to

the reduction in rung resistance, and are provided only for

reference.

From the results it can be seen that the measurements taken

are as expected, as bolts are removed the resistance across the

splice increases. The addition of the earth bonding wire in the

case for finger tight bolts provides a reasonably consistent

value as bolts are removed from the one side. As bolts are

removed from both sides of the splice plate the resistance

varies considerably, indicating that the splice plate is

providing the majority of conductivity.

Interestingly the finger tight tests provided a low resistance

value without the bonding wire and with only a small

improvement of around 10 to 11% with the bonding wire

attached. The case of torque bolts shows that the splice plate

provides a very low resistance, and little improvement was

measured with the addition of the bonding wire, around 1.74%

with all tightened bolts. The use of a larger bonding wire

25mm2 also proved little advantage in reducing the effective

resistance, as the percentage improvement is only 0.7% against

using the 16mm2 wires.

Comparing the measurements between a straight 2m length

of ladder, at 629.0 µ to the tested joint section without a

bonding wire of 481.0 µ, shows that the tested splice section

has less resistance than a nominal section of ladder, this can be

attributed to the paralleling effect of the splice plate with the

ladder rail sections. Also comparing a length of ladder with

copper cable shows that a one meter length of cable ladder has

less resistance than a 600mm length of cable, 16mm2 or

TPMJH-201001

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25mm2. In fact the resistance of ladder would be comparable

to copper cable a little greater than 50mm2. If the resistance of

the splice section under test is compared, we obtain a cable

that would be equivalent to almost 95mm2 copper cable.

V. DISCUSSION

A. General

Theoretical results show that the bonding wire has a small

advantage, around 15% in reducing the resistance at the splice

section, however this result is only based on using an isolated

section of ladder, localised at the splice joint. This is only

across a short distance of 540mm, not a complete ladder

length.

The findings presented from the testing shows that the

bonding wire provides almost no value in reducing the

resistance across the splice plate; however this testing is

performed over an increased distance of 2 meters compared

with the theoretical result. Further, the effectiveness should be

calculated over complete lengths of ladder which are joined

together to obtain a better representation. To determine how

the testing point locations affects the results a look at end to

end resistance is required.

B. End to End Resistance

End-to-end resistance refers to the location of the measuring

points along the length of the ladder system and the effect that

this has when the test points are moved further away from the

splice plate location. Thus assuming a linear resistance value

per meter for the ladder section and another value for the

splice section, located within a small bounded region, and then

comparing this with installing a bonding wire to further reduce

the resistance of the splice region.

The effect then of end-to-end resistance is the change in

resistance as measured as the points are moved outwards from

the centre, and as a result the resistance increases due to the

linear addition of the ladder length the further the

measurement points are moved away, and as such the

advantage (reduction in resistance) of the bonding wire

becomes less the further the measurement points are moved

out. This is further shown by formula (2).

laddersplice RLR totalR (2)

Where;

L = length of ladder minus splice [m]

Rladder is for a 1m section

Combining (1) and (2) to obtain (3).

laddersplice

ladderwirespliceladdersplice

RLR

RLRRLR

||%I (3)

From (3) it can be shown that as L is increased then the

addition of Rsplice and Rsplice||wire is significantly reduced. If this

theory is applied to two infinite lengths of ladder joined

together, then as the test points are taken to infinity, the

improvement by equation (3) would reduce to zero.

For the case where two 6m ladder sections are connected

with a splice plate and comparing the resistance from each

end, i.e. 12m apart with and without the earth bonding wire we

obtain the following resistances.

With no bond wire – 3,705.8 µ

With bonding wire – 3,697.6 µ

Then using (1) the improvement calculated by adding the

bonding wire is 0.22%, a very small improvement. Conversely

if we look at conductance instead of resistance, taking the

inverse of the above values and calculating the improvement

using (1) in terms of conductance we obtain;

With no bonding wire – 3,705.8 µ 269.847 Siemens

With bonding wire – 3,697.6 µ 270.445 Siemens

The improvement by adding the bonding wire is 0.598

Siemens, the percentage improvement however remains the

same at 0.22%, as the value of change remains proportional,

the percentage improvement anyhow is basically zero.

C. Risk of Splice Joint Failure

To look at the risk associated with not having a bonding

wire attached the following assumption is made; the splice

joint provides no benefit, hence the reason for the bonding

wires. The risk is that the cable ladder earthing system fails to

provide a continuous earth path.

It appears reasonable to argue that a failure might be

rendered by 3 possible events; corrosion induced – fracture

and failure of a bolt or bolts – a bolt or bolts that have come

loose, any of which would then allow the splice plate and rail

to open up, all 3 events then leading to a high resistance joint

and therefore reducing the conductivity of the ladder system.

The probability of a failure of one bolt or bolts (be it a

bonding wire bolt or a splice plate bolt) is difficult to

determine and a figure is not assumed, rather one method is

compared to another. If a system is relied on with a single

bonding wire then if a single bolt fails, the complete earthing

system fails. However if two bonding wires are installed, one

on each of the side rails, then the probability would be halved,

assuming the events are independent, in other words, would be

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considered twice as unlikely to fail compared with the single

wire bonding method.

For the case where splice plates are deemed suitable and no

bonding wires exist then there are 8 bolts in each splice plate,

thus for a ladder splice there are 16 bolts in total making an

earth connection. If for the worst case bolts failed only on one

side, 8 bolts for a total failure then the probability of this

system failing would be 8 times less likely to fail than for the

first case relying on a single bonding wire. The splice method

is therefore offering very good odds against a failure of the

earthing system.

For the case where cable ladder is purposely broken, then if

two bonding wires are installed, one to each side rail, the

probability of a complete failure is less likely by a factor of

two. Thus this would be a preferred method for bonding and

earthing in this situation due to the reduced risk involved.

It would be very unlikely that a bolt would fail under normal

conditions, correctly tightened and with minimal vibration.

However failure may be caused by the following; over-torqued

bolts at installation that later fail due to vibration; bolts that

had not been tightened (i.e. finger tight) during installation and

later falling out; corrosion or build up at the splice joint due to

chemicals or mineralised water if the cable ladder has been

installed in severe environments.

The risk of a bolt failure is significantly small under normal

conditions, and can be reduced, by proper tightening and

verification, routine inspection and maintenance which would

also affect any bonding wires being used.

VI. PROBING FURTHER

Investigating other practices from standards of other

organisations gives the following:

NEMA standard VE 2 Section 4.7.1 Cable tray used as an

Equipment Ground Conductor (EGC) states the following;

“The use of aluminium and steel cable trays is permitted as

an Equipment Grounding Conductor per NEC Article 392

when labelled and marked with the available cross sectional

area. (See Table 4-4.) If the cable tray is to be used as an EGC,

bonding jumpers must be installed on both side rails at the

locations illustrated in figures 4.57 through 4.60, unless the

splice plates meet the electrical continuity requirements of

NEMA VE 1. See table 4-5 for minimum sizes of grounding

conductors.

If the connectors are UL Classified bonding jumpers or a

continuous ground are not required.

It is not necessary to install bonding jumpers at standard

rigid aluminium or galvanised steel splice plate connectors or

offset reducing splice plate connectors or any UL Classified

connectors.

For rigid splice plate connections of materials and finishes

other than aluminium or galvanised steel, bonding jumpers

may be required. For example, stainless steel splice plates may

require bonding jumpers depending UL Classification.”

Section 4.8 – Bonding to steel and earth;

“Metallic cable trays shall be bonded to building steel and

earth as supplemental grounding for ground fault protection

and signal grounding (noise prevention). The tray shall be

bonded to building steel and earth, at least every 18m (60 ft).

This is only required when cable tray system is not inherently

bonded (connected) to building steel and earth metallic

support systems”.

NFPA 70 Article 392.7 (B) states;

“Steel or aluminium cable tray systems shall be permitted to

be used as equipment grounding conductors, provided all the

following requirements are met:” Specifically part (4) states,

“Cable tray sections, fittings, and connected raceways are

bonded in accordance with 250.96, using bolted mechanical

connectors or bonding jumpers sized and installed in

accordance with 250.102.”

Cable Tray Institute, Technical Bulletin Number 8, Titled

‘Bonding Jumpers Not Required for Standard Cable Tray

Splice Plates’ states;

“It is not necessary to install bonding jumpers in parallel

with the standard rigid aluminium or steel one-piece metallic

bolted side rail splice plates that are the connections between

the tray sections. Here, the use of bonding jumpers does not

make a safety contribution to a properly installed cable tray

system, and wastes both materials and labour.”

From the above excerpts it is clear that other standards do

not require cable ladder to have additional bonding using earth

wires, and in the case of NFPA and NEC actually allows the

use of cable ladder as an earthing conductor to earth

equipment back to the main earth.

VII. CONCLUSION

For the tested galvanised steel cable ladder, it is concluded

that bonding wires are not required to bond across the standard

splice plates, as the benefit of such a practice is negligible and

provides no addition safety merits.

As for not installing bonding wires, the risk is very low due

to the large number of bolts being used in the splice plates.

The most important bonding connection is the connection of

the cable ladder system to the main earth. Splice plate

bonding wires need only be installed where gaps have been left

in the cable ladder to reinstate a continuous earthed ladder

system.

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VIII. PROPOSED INSTALLATION PRACTICE

In light of the findings from the results of cable ladder

testing, discussions and further information, the following

points are put forward as proposed installation guidelines for

installing cable ladder.

Cable ladder shall be earthed back to the main earthing

system via two main earth conductors, or via one earth

conductor with a loop installed to each side rail.

Bonding between cable ladder sections is provided with

the slice plates and no additional earth wire conductors

are required.

Where cable ladder sections are separated and are not

joined via splice plates, two off earth conductors shall

be provided to maintain a continuous earth.

Where expansion gaps or sliding expansion joints are

used a bonding earth wire shall be installed to maintain

a continuous earth.

Where adjustable splice plates are used, these shall

include an earth bonding cable unless the plates meet

continuity requirements, (as per NEMA Standard VE

1).

Develop/use a testing or inspection procedure to ensure

that spice plate bolts have been tightened correctly after

installation has been completed.

The figures 6 and 7 show earth bonding requirements for the

types of ladder splice plates; adjustable vertical plates, and

horizontal adjustable plates. These require bonding wires as

they would not offer good conductivity due to the hinged

joints, and use of only one bolt.

Fig. 6. Cable tray sections, vertical adjustable splice plate showing bonding

wires.

Fig. 7. Cable tray sections, horizontal adjustable splice plate showing

bonding wires.

ACKNOWLEDGMENT

The author thanks Kounis Metal Industries and David

Kounis, Sheet Metal Manager for providing cable ladder,

premises, materials and test equipment for performing the tests

required for the paper.

REFERENCES

[1] AS3000-2009 - The wiring Rules.

[2] NEMA Standard VE 2-2006 – Cable Tray Installation Guidelines.

[3] NEC NFPA 70-2008 (Article 392)

[4] Olex Cable Handbook.

[5] Web – Cable Tray Institute – Cable Tray Installation.

[6] Cable Tray Institute, Rosslyn, Virginia USA, Technical Bulletin

Number 8.

[7] Cooper B-Line Cable Tray Manual.

Michael J. Hamilton (M’98) received the bachelor of engineering degree

with honours in electrical engineering from Curtin University of Technology

of Perth WA, Australia, in 2000.

He is currently Senior Electrical/Controls Engineer for Langkilde

Engineering Services an engineering company located in Burswood, Perth,

Western Australia. His previous work experience includes Electrical

Engineer positions at EPCM companies and site positions in engineering and

maintenance departments within the mining industry at BHP Billiton Iron Ore

Port Operations, Western Mining (WMC) Nickel Smelter Operation and

Goldfields Australia, St Ives Gold Operation.

Mr. Hamilton is member of IEEE and a committee member of the

Goldfields Electrical Industry Group situated in Kalgoorlie. He was a

recipient of the Best Student Paper Award from the IEEE Power Engineering

Society in 1999.

Cable Ladder Bonding with Earth Wire, Is it Necessary?

Engineering

Transcript of Cable Ladder Bonding with Earth Wire, Is it Necessary?