service grounding

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bobbymari

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los angeles ca
Torn on Gec cold water connection.
We have a multi family apt that has detached buildings.
Our service is mounted on the opposite building of the main cold water entry.
We are torn whether we should take our gec to where the water enters the building that our gear is on or to where the actual main point of entry which is the detached building.
This is a 400 amp multi meter modular setup.
 
If the main water service is metallic then IMO you need to take the GEC to within 5' of where it enters the building. I have not looked it up, but I know there are some exceptions that will not apply to residential.
 
edward said:
If the main water service is metallic then IMO you need to take the GEC to within 5' of where it enters the building. I have not looked it up, but I know there are some exceptions that will not apply to residential.
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Right thats the question. Where it enters the building that our gear is on or where the main cold water enters which is the detached building.
One building feeds the others water in other words
 
You need to run grounding electrode conductor at a particular building or structure to all qualifying electrodes at that building or structure.

If an electrode is at a separate building it does not need direct connection to equipment at another building.

Keep in mind that conductive paths between the two buildings (like a metal water pipe) make you have to run a separate EGC between the two buildings where exceptions may otherwise allow "re-grounding" the grounded conductor at the second building.
 
Note that you need to consider the water line as it pertains to the building in question only.
By that, I mean if the main water line into the detached building qualifies as a grounding electrode due to 10 ft or more metallic pipe in contact with the earth, but the pipe coming into your building does not meet the same qualification then it would not be an electrode as far as your building is concerned. (Interior metallic piping would still need bonding but 250.104 would apply rather than 250.52)
 
I believe the OP has a structure with the main electrical service on it then a separate detached building/structure where the main water comes in. IMO he needs to get his GEC to the building/structure where the main utility water supply comes in.
 
And if you're running feeders to any of those other detached buildings, you'll need to run a GEC in those buildings too, to the feeder panel, and connect within 5' of where the water enters that particular building. Size of the GEC at those other buildings is based on the size of the building feeder, not the original service.

If the building where the water enters first from the utility has no power, then that building gets no GEC.
 
augie47 said:
Note that you need to consider the water line as it pertains to the building in question only.
By that, I mean if the main water line into the detached building qualifies as a grounding electrode due to 10 ft or more metallic pipe in contact with the earth, but the pipe coming into your building does not meet the same qualification then it would not be an electrode as far as your building is concerned. (Interior metallic piping would still need bonding but 250.104 would apply rather than 250.52)
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Thank you all. Got it
 
edward said:
I believe the OP has a structure with the main electrical service on it then a separate detached building/structure where the main water comes in. IMO he needs to get his GEC to the building/structure where the main utility water supply comes in.
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No, the separate building has a separate water entrance, and it is only a qualifying electrode if there is 10 feet or more of metallic pipe in the earth. Doesn't matter if that water pipe comes from another building, a private water system, a municipal water system, etc, it is an electrode that must be used if it is a qualifying electrode.

If this water pipe is not qualifying electrode there is no requirement to run a GEC back to the building where the service is located.
 
kwired said:
No, the separate building has a separate water entrance, and it is only a qualifying electrode if there is 10 feet or more of metallic pipe in the earth. Doesn't matter if that water pipe comes from another building, a private water system, a municipal water system, etc, it is an electrode that must be used if it is a qualifying electrode.

If this water pipe is not qualifying electrode there is no requirement to run a GEC back to the building where the service is located.
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Got a visual. :thumbsup:
 
edward said:
Got a visual. :thumbsup:
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I bet MH or someone in similar capacity does, I do not.

But I will say to read 250.50 carefully.

All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.
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It says "that are present at each building or structure served". It does not mention anything about needing to bond to something at another structure. When you are supplying one building from another you start from scratch when applying your grounding electrode system and only apply what electrodes are available at your second building when doing this.

You also do not need to run a GEC back to first building because the first building has a CEE or building steel. If the second "structure" is just a post or something of that nature you may not have any naturally existing elecrodes - you then must install a "made" electrode - of which a ground rod(s) is most popular choice.
 
kwired said:
No, the separate building has a separate water entrance, and it is only a qualifying electrode if there is 10 feet or more of metallic pipe in the earth. Doesn't matter if that water pipe comes from another building, a private water system, a municipal water system, etc, it is an electrode that must be used if it is a qualifying electrode.

If this water pipe is not qualifying electrode there is no requirement to run a GEC back to the building where the service is located.
Click to expand...

This is our setup. So now im thinking both water lines are considered electrodes needing to be joined? The underground subfeeds to 2nd building are 60amp not 6 amp oops
 

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bobbymari said:
This is our setup. So now im thinking both water lines are considered electrodes needing to be joined? The underground subfeeds to 2nd building are 60amp not 6 amp oops
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NEC is satisfied with running a GEC from the service/main supply at each building to the water supply at each building.

The fact that water pipe happens to run between the two buildings doesn't matter, the fact there is 10 or more feet of metallic water pipe that is underground entering the building means it is a qualifying electrode and must be bonded to the electric supply of that building whether it is service or feeder or other separately derived source supplied.
 
Each building needs it's own grounding electrode system. You do not have to consider what is in some other building when designing the GES at a particular building or structure, just what electrodes are present at that building or structure.
 
kwired said:
No, the separate building has a separate water entrance, and it is only a qualifying electrode if there is 10 feet or more of metallic pipe in the earth. Doesn't matter if that water pipe comes from another building, a private water system, a municipal water system, etc, it is an electrode that must be used if it is a qualifying electrode.

If this water pipe is not qualifying electrode there is no requirement to run a GEC back to the building where the service is located.
Click to expand...

kwired said:
Each building needs it's own grounding electrode system. You do not have to consider what is in some other building when designing the GES at a particular building or structure, just what electrodes are present at that building or structure.
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Thank you thats what im after.
service building electrode system based on 500 mcm serv entry cond i/e 1/0 copp ground
Secondary building electrode system based on #6 subfeeds i/e #10 copp ground
 
kwired said:
I bet MH or someone in similar capacity does, I do not.

But I will say to read 250.50 carefully.



It says "that are present at each building or structure served". It does not mention anything about needing to bond to something at another structure. When you are supplying one building from another you start from scratch when applying your grounding electrode system and only apply what electrodes are available at your second building when doing this.

You also do not need to run a GEC back to first building because the first building has a CEE or building steel. If the second "structure" is just a post or something of that nature you may not have any naturally existing elecrodes - you then must install a "made" electrode - of which a ground rod(s) is most popular choice.
Click to expand...

I meant I understood it.
 
bobbymari said:
Thank you thats what im after.
service building electrode system based on 500 mcm serv entry cond i/e 1/0 copp ground
Secondary building electrode system based on #6 subfeeds i/e #10 copp ground
Click to expand...

Note that the smallest conductor in table 250.66 is #8 copper. So for a feeder with #6, you need a #8 copper GEC. And with #8 you also need to run it in conduit to protect it from damage, so I'd be using #6 or #4 to make it easier.
 
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