Manhole Bonding

[cjreng2014]

If you have a pad mount utility transformer with service conductors on the secondary (3-Phase, and 1-Neutral) that run through a manhole, would you bond all the metal parting together and bond them to the service neutral within the manhole or could you bring a equipment grounding conductor from the ground bus in utility transformer to manhole and bond them this EGC.

It appears to me that all the manhole details I've seen have all the metal bonded together and bonded to a ground rod, which in my opinion doesn't accomplish anything.

Any thoughts?

 

[cjreng2014]

How about this, can you bond all metal parts together inside the manhole and connect these to the grounded service conductor?

 

[tkb]

Use fiberglass manhole racking and brackets and you won't need to worry about the grounding.

 

[cjreng2014]

What about the manhole cover?

 

[tkb]

What about the manhole cover?

I have been in several manholes and never seen a cover grounded.

 

[Fulthrotl]

I have been in several manholes and never seen a cover grounded.

it's intrinsically grounded when it's in the embedded ring.

when it's not in the ring, it's scrap iron, or at least the tweekers and metal thieves around here
seem to think so.....

 

[Smart $]

Are we talking manhole or handhole???

For a handhole, see 314.30. In particular thereunder...

(D) Covers. Handhole enclosure covers shall have an identifying
mark or logo that prominently identifies the function
of the enclosure, such as “electric.” Handhole enclosure
covers shall require the use of tools to open, or they shall
weigh over 45 kg (100 lb). Metal covers and other exposed
conductive surfaces shall be bonded in accordance with
250.92 if the conductors in the handhole are service conductors,
or in accordance with 250.96(A) if the conductors
in the handhole are feeder or branch-circuit conductors.

If we are talking manhole, go directly to 250.92.

 

[tkb]

Are we talking manhole or handhole???

For a handhole, see 314.30. In particular thereunder...


If we are talking manhole, go directly to 250.92.

Seems like a roundabout way to get the covers grounded.
They should add the word "cover" to articles 250.92(A) and 250.96(A)

 

[Smart $]

Seems like a roundabout way to get the covers grounded.
They should add the word "cover" to articles 250.92(A) and 250.96(A)

Covers are a part of an enclosure... and enclosures are specified in 250.92(A)(2) and the general statement of (A) says normally non-current-carrying metal parts. Note exactly how to bond manhole/handhole covers is not stipulated.

 

[tkb]

Covers are a part of an enclosure... and enclosures are specified in 250.92(A)(2) and the general statement of (A) says normally non-current-carrying metal parts. Note exactly how to bond manhole/handhole covers is not stipulated.

I still think it's a little vague, but I have never seen a manhole or handhole frame or cover with grounding provisions.

 

[Smart $]

I still think it's a little vague, but I have never seen a manhole or handhole frame or cover with grounding provisions.

Neither have I.

Where the ones I've experienced were metal I imagine they met the 100lb requirement of 110.75(D) or 314.30(D)... i.e. I didn't weigh them. From there we go to the comment made by Fulthrotl (Randy, IIRC) about being intrinsically grounded by contact with the hole frame... and I've not seen a hole with metal cover that did not also have a metal hole frame... but as you said I too have not seen grounding provisions for the frame. Granted, even if the frame is bonded, I do not see this complying with 250.92.

So what shall we do about it? :blink:

 

[cjreng2014]

I've seen several manhole grounding details that simply bond all the metal parts together to a ground rod inside the manhole, but no one seems to bond it to the grounded (neutral) conductor. I think this misses the point and will not return a ground fault to the source. Does anyone know how this is done? with 600V and under service conductors?

 

[Smart $]

I've seen several manhole grounding details that simply bond all the metal parts together to a ground rod inside the manhole, but no one seems to bond it to the grounded (neutral) conductor. I think this misses the point and will not return a ground fault to the source. Does anyone know how this is done? with 600V and under service conductors?

FWIW, I didn't miss that point the first time around. All I can say is Code requires bonding the same as all other enclosures and parts thereof.

You can run a bonding jumper rather than splice/tap the grounded conductor(s) in the manhole. In instances I've been involved with, a bonding jumper embedded in the duct bank and bonds all the non-ccc metal parts within the hole (ladder, racks, etc.) but have never seen a jumper to the hole frame or cover. I've never been part of fabricating a manhole, so I cannot say whether or not the hole frame was bonded with the jumper embedded in the concrete.

 

[cjreng2014]

That would be a supply-side bonding jumper that would terminate at the service disconnect, correct?

 

[Smart $]

That would be a supply-side bonding jumper that would terminate at the service disconnect, correct?

Not necessarily. There is no requirement in Article 230 that an SSBJ terminate at the service disconnect. The only place the term is even used in the entire article is 230.43(15) regarding the use of up to 6ft of FMC/LFMC... a technical correlation with 250.102, new in 2014 NEC. Connecting to the grounded service conductor at some point would be all that is required assuming all other aspects such as size, routing, etc. are compliant. Also need to consider the possibility of creating a parallel grounded conductor current pathway.

 

[cjreng2014]

there wouldn't be parallel paths correct because you would bring the supply side bonding jumper back to the main switchboard ground bus, which would connect to the main bonding jumper and to the service neutral. so if a fault occurred on say the cable rack, the current would flow from the rack to the supply side bonding jumper to the main switchboard ground bus, over the main bonding jumper and back to the service on the service neutral. Where would the parallel path be?

 

[Smart $]

there wouldn't be parallel paths correct because you would bring the supply side bonding jumper back to the main switchboard ground bus, which would connect to the main bonding jumper and to the service neutral. so if a fault occurred on say the cable rack, the current would flow from the rack to the supply side bonding jumper to the main switchboard ground bus, over the main bonding jumper and back to the service on the service neutral. Where would the parallel path be?

That wouldn't be a parallel path, but the SSBJ could be run all the way to the transformer and one may be inclined to bond it there. Or perhaps bonding to the grounded conductor at more than one point.