Grounding of Utility Manhole

Status
Not open for further replies.
mshields

mshields

Senior Member
Location
Boston, MA
I'm doing a high rise building where we happen to be putting a utility manhole on ground floor of our garage. i.e. in the building. The utility requires a ground rod in their manhole. Should that ground rod tie into our grounding electrode system for the building.

I'm thinking no just as if the manhole were outside of our building we wouldn't do anything with it.

Also, our grounding electrode system for the building goes back to it's source, the service transformers, the manhole grounding system would be completely independent.

Agree? Disagree?

Thanks,
 
Not being a "Manhole" kind of guy I'm going to ask what all is in this manhole. Where is the Grounding electrode conductor going to terminate? The way I see it the cover if energized will not comply with 250.4(A)(5) or 250.4(B)(3). Again I don't do manholes and for me this is a very good question because "Murphy's Law" says tomorrow I will inspect one. I cannot see any redeeming feature for a ground rod at that point. Of Course then again if it is a utility manhole it is not for me to inspect come to think of it but I have heard stories of people dying due to unbonded manhole covers.

Andrew
 
People dying from improperly grounded manholes

People dying from improperly grounded manholes

Me too. And I've read how the utility routinely grounds light poles improperly. i.e. such that a ground fault does not go back to the source and provide enough current to trip the overcurrent device.
 
Grounding of Utility Manhole

If the manhole is something that I am installing I would bond it to the service equipment ground no matter what the utility says.

Cleveland Public Power has killed at least 1 person with an unbonded handhole or manhole cover where a 480 volt streetlighting circuit energized the cover. This happended when it was raining. I do not know if a wire made direct contact with the cover or if the handhole filled with water which completed the circuit with say a place where a mouse chewed on the wire. What one of the other guys at International Exposition Center said to me about their 480 volt streetlighting handholes before opening it went something like, "Be very careful in these things. Mice Chew on the wires." I then vacuumed out the handhole and found no dead mice but plenty of places where mice had chewed on the wires.

Somebody else got toasted after USA Today installed a vending machine and accidentally drilled into a Cleveland Public Power streetlighting conduit that was just a few inches below a sidewalk. Since 480 volt streetlighting circuits are deenergized by a central controller there was no sparking during the drill-in. Next time it rained at night USA Today killed one of their customers. Cleveland Public Power was exonerated of any liability because the conduit was "Code" depth below the sidewalk. NEC burial depth below a public sidewalk is bogus.
 
An omission in my question

An omission in my question

This is a MV manhole bringing service to the building. So again, I don't think it's appropriate to ground it to the buildings grounding electrode system.

Thanks for all of your responses. I look forward to more now that I've clarified what we're talking about.

Thanks,
 
mshields said:
This is a MV manhole bringing service to the building. So again, I don't think it's appropriate to ground it to the buildings grounding electrode system.

Thanks for all of your responses. I look forward to more now that I've clarified what we're talking about.

Thanks,
Click to expand...

If you have a grounded wye medium voltage system, their ground is almost certainly tied your grounding electrode system already. Most utilities have a common neutral system, one wire for both primary and secondary. That neutral is their ground also. So when you bond neutral and ground at the service disconnect you are attaching to their ground wire.

I agree that being sure the manhole is grounded is more important than worying about another connection to your GEC system.

Jim T
 
Status
Not open for further replies.
Top