manhole grounding requirement

[a10jp]

Just want to reassue my understanding of the requirement of bonding/grounding in manholes. My understanding is the requirement is only applicable if splicing of cables is done inside the manhole, and where the manhole is used only for pull-thru of the cable, there is no bonding requirement in that manhole, including any metal steps, etc. Is that statement correct?

 

[a10jp]

I should add the conduit through the MH is PVC, not metal.

 

[ScottyUK]

Likely depends on the national code - what country are you in?


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If we learn from our mistakes I'm getting a great education!

 

[a10jp]

I am in Japan. But this is a US funded project, so I am following US code. However, even in US code, if these MH are not meant for termination or splicing work, I do not see any logic in putting in grounding. Just wondering if others feel the same.

 

[alehman]

I don't think the NEC requires grounding of metal components in manholes unless it is an exposed metal cable shield, splice or termination. Some utilities have started requiring grounding of covers.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[prc]

I have seen separate grounding of man hole covers in EHV power transformers.Some manufacturers use the fixing bolts as the equaliser connection.

 

[7anoter4]

If the manhole is provided with metallic cable trays, metallic conduits for communication cable, control cable or analog signal, metallic ladder our practice is to connect this to the grounding grid. A suitable conductor of copper- bare or lead or tin covered- run along the cable duct and if it required a grounding electrode is provided in a manhole bottom corner. But this is large power station yard practice.

 

[cgrodzinski]

a10jp, what voltage of the power cables we are talking about?

Generally, if there is any metal part that is in the same compartment and it is not intended to be energized - it should be grounded. It means that if you have supporting structures for the cables in the pull-thru manhole they should be grounded to a local ground. In some jurisdictions even the manhole covers are grounded. The ground resistance must be within a local regulations requirements.

 

[a10jp]

Hi, the cable that is feeding thru is a 6.6kV cable. We have no splicing or termination anywhere, just pull thru only. SOme has raised the concern, if the insulation fail along anywhere of the cable, and leakage current occurs, then if someone were inside the manhole at the same time and location will be hazardous, and felt gronding is required. I wonder becasue this is a MV cable, does it make the requirement a little different?

 

[alehman]

There may not be any "requirement" for grounding. That is up to your local codes or corporate standards, if any apply.

Medium voltage cable is normally shielded, so an insulation failure would result in current flow between the conductor and shield. Normally that results in a nearly instantaneous trip of your overcurrent protection.

For medium voltage cable, the greater hazard is that the ground connection(s) to the shield could be broken which could cause the shield to become energized. In most installations the shield is grounded at at least two locations.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[a10jp]

Thanks Alan. In our case in Japan, the shield of the cable will be grounded at the incoming service of the distribution panel (US side), which has a dedicate ground. But at the utility pole (Japan side), since it is ungrounded delta, there is not ground on that side. There is only one ground at the pole which is dedicated only for the arrestor inside the primary cut-off switch, according to local requirment.