Xfmr bonding

[electricalist]

All concrete structure. Bond for bldg MDP is not accessible from our end of the bldg without Sheetrock damage in the ceiling down the hall.
Any suggestions on where to bond.
There is cold water in our space but nothing that is before a valve and 10' in contact with earth.
Thanks


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[Smart $]

You got to do what you have to do.

Have you considered running a combo GEC/EGC with supply conductors?

250.121 Exception.

 

[electricalist]

The feeder conduit was pre ran by bldg EC. So 3/0 w/ E.G. was pulled into space. Then the XFMR brought up the how to bond the GEC.
I'm gonna ask the AHJ what he suggests.


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[Smart $]

...
I'm gonna ask the AHJ what he suggests.
...

Certainly can't hurt.


What size EGC with primary conductors? Run in metal or plastic? Transformer configuration and rating?

What type of facility? 250.68(C) is where the requirement for nearest electrode, water pipe or structural steel is required before going to others. The exception therein permits bonding beyonfd the 5' normally permitted. There is nothing in the requirement which restricts usage depending on valve locations. Specific wording...

Exception: In industrial, commercial, and institutional buildings
or structures, if conditions of maintenance and supervision
ensure that only qualified persons service the installation,
interior metal water piping located more than 1.52 m (5 ft)
from the point of entrance to the building shall be permitted as
a bonding conductor to interconnect electrodes that are part
of the grounding electrode system, or as a grounding electrode
conductor, if the entire length, other than short sections passing
perpendicularly through walls, floors, or ceilings, of the
interior metal water pipe that is being used for the conductor
is exposed.

 

[electricalist]

#6 EGC ,3/0 feeders , 2.5 EMT. 150 amp 480v to MLO 90 amp breaker feeds XFMR. 120 /208 Y


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[electricalist]

AHJ said cold water in the space is all you have to work with then so be it.
It's a lease space within a strip center.
Multiple tenant spaces on the first floor , parking on the 2nd floor


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[iwire]

AHJ said cold water in the space is all you have to work with then so be it.
It's a lease space within a strip center.
Multiple tenant spaces on the first floor , parking on the 2nd floor


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You got lucky, the NEC requires that GEC go back to the Grounding electrode system.

It is worth pointing out that when an inspector does this it is still a violation and can come back on you at any time in the future.

 

[Smart $]

You got lucky, the NEC requires that GEC go back to the Grounding electrode system.
....

It is not stated that way. Code requires the SDS' GEC to be run to the nearest of a metal water pipe electrode* or the building structural steel electrode if either exists. If neither exists, then one of the other electrodes of the existing GES.

*Under the exception to 250.68(C) quoted above, he can use the local metal water pipe... subject to the "qualified persons only" condition.

 

[iwire]

It is not stated that way. Code requires the SDS' GEC to be run to the nearest of a metal water pipe electrode* or the building structural steel electrode if either exists. If neither exists, then one of the other electrodes of the existing GES.

*Under the exception to 250.68(C) quoted above, he can use the local metal water pipe.

Damn my friend, do you always have to be so nit picky?

You posted the exception, we can all see it, I was aware of it, have used it before and I did not dispute it.

However the OP stated running a GEC back would cause sheetrock damage, this strongly suggests this part of the exception will be an issue.

if the entire length, other than short sections passing
perpendicularly through walls, floors, or ceilings, of the
interior metal water pipe that is being used for the conductor
is exposed.

 

[iwire]

FWIW I am only talking about the NEC and not what I think is safe vs unsafe.

These SDS GEC requirements get silly to me. When we wire a brick and wood mill building and have to run a GEC down 5 floors right beside a EMT with a wire EGC that will electrically connect at both ends. :roll:

Unless we already wasted T&M installing a common GEC previously. :roll:

 

[Smart $]

Damn my friend, do you always have to be so nit picky?

The Scorpion and the Frog

A scorpion and a frog meet on the bank of a stream and the
scorpion asks the frog to carry him across on its back. The
frog asks, "How do I know you won't sting me?" The scorpion
says, "Because if I do, I will die too."

The frog is satisfied, and they set out, but in midstream,
the scorpion stings the frog. The frog feels the onset of
paralysis and starts to sink, knowing they both will drown,
but has just enough time to gasp "Why?"

Replies the scorpion: "Its my nature..."

However the OP stated running a GEC back would cause sheetrock damage, this strongly suggests this part of the exception will be an issue.

That portion is regarding the metal water pipe, not the GEC. His statement about the hard top was regarding running a GEC I believe, and wasn't specifically about the water pipe as far as I can tell... but it is a definite possibility.

 

[iwire]

That portion is regarding the metal water pipe, not the GEC. His statement about the hard top was regarding running a GEC I believe, and wasn't specifically about the water pipe as far as I can tell... but it is a definite possibility.

In what we humans call the real world it is.

 

[electricalist]

When this lease space first started the floor was saw cut for plumbing. If I would have ran a CEE in the slab , could this been acceptable?


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[electricalist]

Would this have been acceptable ?


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[Smart $]

When this lease space first started the floor was saw cut for plumbing. If I would have ran a CEE in the slab , could this been acceptable?

A CEE goes in a footing (aka footer)... so in the slab, no.

If the building has an existing metal water pipe electrode or structural steel electrode, you are required to use the nearest. I believe you have already established one of those electrodes exists.

 

[Smart $]

F...
These SDS GEC requirements get silly to me. When we wire a brick and wood mill building and have to run a GEC down 5 floors right beside a EMT with a wire EGC that will electrically connect at both ends. :roll:
...

This is where you run an EGC/GEC combo... once again permitted under 2014.

 

[Strathead]

A CEE goes in a footing (aka footer)... so in the slab, no.

If the building has an existing metal water pipe electrode or structural steel electrode, you are required to use the nearest. I believe you have already established one of those electrodes exists.

I wonder. I agree from the wording your answers are spot on, but I couldn't help but wonder if the OP or his Engineer has established that the water pipe in the building does, in fact, qualify as a grounding electrode.

 

[gadfly56]

I wonder. I agree from the wording your answers are spot on, but I couldn't help but wonder if the OP or his Engineer has established that the water pipe in the building does, in fact, qualify as a grounding electrode.

You never know where someone has cut into the system with PEX or something similar.

 

[electricalist]

A CEE goes in a footing (aka footer)... so in the slab, no.

If the building has an existing metal water pipe electrode or structural steel electrode, you are required to use the nearest. I believe you have already established one of those electrodes exists.

My assumption was in hopes that if I'm bonded to the rebar in the existing slab that also mechanically connected to the MDP bond at the other end of the bldg, it's about as reliable as jumping on a cold water pipe in my space.


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[Strathead]

My assumption was in hopes that if I'm bonded to the rebar in the existing slab that also mechanically connected to the MDP bond at the other end of the bldg, it's about as reliable as jumping on a cold water pipe in my space.


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Can't be verified, can't be assumed, in my opinion.