Grounding a XFMR for Tenant Space

[charlie b]

Large shopping mall. New tenant requires their own step-down transformer. Owner won't allow GEC to be run from transformer to ground bar in main electrical room. Owner says that the local inspector lets all the tenants connect to the copper water pipe that is closest to their individual space. I am crying "foul!" They are pushing back. Am I missing something? :?

 

[augie47]

It would appear the local inspector might be stretching 250.104(A)(2).....

 

[don_resqcapt19]

Large shopping mall. New tenant requires their own step-down transformer. Owner won't allow GEC to be run from transformer to ground bar in main electrical room. Owner says that the local inspector lets all the tenants connect to the copper water pipe that is closest to their individual space. I am crying "foul!" They are pushing back. Am I missing something? :?

I don't know of a requirement that you run a GEC back to the building grounding electrode system, but I do know that you cannot make the required grounding electrode connection to the local water pipe. You are required to make a bonding connection to the local water pipe.

I think I would just drill holes in the floor, install two ground rods, and a #6 GEC to XO at the transformer and make the code required water pipe bonding connection.

 

[GoldDigger]

Looks like shirt pocket code to me.
Allowing a non compliant solution is one thing, but prohibiting a compliant solution is another. But I see it is the owner who is taking that position.
It is your license on the line but if the owner (who is or is not your customer?) and the inspector agree I am not sure you have any leverage. Possibly the tenant's lease gives them the right to make necessary code compliant wiring changes?
BTW, I might call the conductor you describe a really long bonding jumper, not a GEC. Are you installing a local ground electrode?

 

[charlie b]

The EC suggested drilling into the floor and inserting a ground rod. My problem with that is that the NEC requires all grounding electrodes that are present in a building to be connected together to form a grounding electrode system. So the separate ground rod would still need to be bonded to another electrode somewhere in the building, and the local water pipe does not count.

 

[don_resqcapt19]

The EC suggested drilling into the floor and inserting a ground rod. My problem with that is that the NEC requires all grounding electrodes that are present in a building to be connected together to form a grounding electrode system. So the separate ground rod would still need to be bonded to another electrode somewhere in the building, and the local water pipe does not count.

Does the code prohibit the use of the transformer primary EGC from being used as the required bond between the electrodes?

 

[GoldDigger]

Does the code prohibit the use of the transformer primary EGC from being used as the required bond between the electrodes?

Or is the owner also resisting pulling an ECG for the feeder?
Just make sure it is large enough for the purpose.
Is it a raceway EGC or wire?

 

[charlie b]

Does the code prohibit the use of the transformer primary EGC from being used as the required bond between the electrodes?

Interesting question. I had not thought of that possibility. I know of no reason not to go with this. I will take a look at the code when I get back to my office this morning.

 

[augie47]

Does the code prohibit the use of the transformer primary EGC from being used as the required bond between the electrodes?

Interesting question. I had not thought of that possibility. I know of no reason not to go with this. I will take a look at the code when I get back to my office this morning.

'`11 Code 250.121

 

[iwire]

Large shopping mall. New tenant requires their own step-down transformer. Owner won't allow GEC to be run from transformer to ground bar in main electrical room. Owner says that the local inspector lets all the tenants connect to the copper water pipe that is closest to their individual space. I am crying "foul!" They are pushing back. Am I missing something? :?

No building steel?

We would be required to run back to the main and have had to do so many times.

 

[don_resqcapt19]

'`11 Code 250.121

I did not suggest that the EGC be used as a GEC...I suggested it be used as the bonding conductor between two different grounding electrodes...the main building grounding electrode and electrode for the new SDS.

 

[charlie b]

This one is now OBE, as we used to say in the Navy (they probably still do). The question has been "Overtaken by Events." The EC bonded the transformer's neutral (or the panel's N-G bond, I don't know which) to the nearest copper water pipe, and the local inspector passed the installation. But thanks for the input and the validation of my viewpoint on this issue.

 

[Strathead]

OK, first off, 250.30 allows the water pipe bond with the caveat of 250.52. Second, the system is a separately derived system and it's grounding electrode system is not required to be bonded to the rest of the building to create "grounding electrode system" This doesn't remove the requirement to bond all conductive surfaces that may become energized, to the separately derived grounding electrode system. And in fact, the requirement to generate the electrode system near the point of connection to the system would make running the conductor back to the building system less desirable.

I state that above as an opinion, since grounding has so much nuance, I welcome any corrections.

 

[charlie b]

OK, first off, 250.30 allows the water pipe bond with the caveat of 250.52.

That caveat calls into play the rule about connecting the GEC within five feet of the point that the pipe enters the building. There is a bit of tracing needed, from article to article, to get to that rule. But I think that rule still applies to separately derived systems.

Second, the system is a separately derived system and it's grounding electrode system is not required to be bonded to the rest of the building to create "grounding electrode system"

I have to disagree with this statement. 250.50 speaks of ?all grounding electrodes? that are present in the building. It does not distinguish those associated with the service from those associated with a separately derived system.

And in fact, the requirement to generate the electrode system near the point of connection to the system would make running the conductor back to the building system less desirable.

I have to give you this point. But I don?t think it relieves us of the requirement to bond the water pipe (if that is the electrode of choice) within 5 feet of the building wall.

 

[Strathead]

That caveat calls into play the rule about connecting the GEC within five feet of the point that the pipe enters the building. There is a bit of tracing needed, from article to article, to get to that rule. But I think that rule still applies to separately derived systems.

There is also the caveat about commercial building under maintenance supervision. I am not saying this applies to your project and it is definitely an AHJ rule, but it exists. and was more the part I was referring to.

I have to disagree with this statement. 250.50 speaks of ?all grounding electrodes? that are present in the building. It does not distinguish those associated with the service from those associated with a separately derived system.

This is an area worth further discussion. I believe there is an issue of intent here. I would contend that items 4 through 8 are rods etc. that are installed with the intention of being part of the grounding system. I definitely concede it doesn't say that, but there would be tens of thousands of building in America installed in violation of this, I imagine otherwise. Code 250.54 could be interpreted as bearing this up. If you disagree, then what does "present at each building" mean? A typical ground rod delta is 3 rods 2' on center, often located 10 feet from the building, so what about the grounding system of the next building over that is within that 30 foot sphere?