transformer grounding not available what to do

[kbrandt]

I have a job to install a 25 kva transformer 480 pri.-240/120 sec. its in a basement of a huge building with no way to drive a ground rod and no building steel or water lines around.

Can I use the grounding from the 480 panel that is going to feed the transformer for my grounding of x-former. It will be coming off the 480 panel ground bar.

Never ran into this before.

Thanks for any help.

 

[iwire]

You will need to run the transformer GEC back to the buildings grounding electrode system.

You cannot use the EGC to do it.

 

[hillbilly1]

I've seen people drill through the slab and drive a ground rod, though that's about worthless. They are bound to be other transformers around, I would find out where they are getting their GEC from.

 

[iwire]

We have done a lot of brick and wood mill buildings and we end up having to run back to the service GES. But we would be doing multiple transformers and the code allows the use of a common GEC for those cases.

Here is one of the places we had to do, a lot of it is 5 floors so we had a to run pretty far to get back to the service GES.

 

[cpinetree]

You will need to run the transformer GEC back to the buildings grounding electrode system.

You cannot use the EGC to do it.

Does that mean 2 ground wires in the conduit (if using pvc)? or just 1 wire sized by the larger of the required GEC or EGC?

 

[Strathead]

Does that mean 2 ground wires in the conduit (if using pvc)? or just 1 wire sized by the larger of the required GEC or EGC?

It means one wire, the GEC. There is not EGC from the bonding point of the transformer to the building Grounding electrode system.

 

[david]

Does that mean 2 ground wires in the conduit (if using pvc)? or just 1 wire sized by the larger of the required GEC or EGC?

From the way you asked both questions I am going to assume that the 480 primary originates in a MDP at or near the service location in this building. I think you are asking if the GEC from the SDS has to be a separate conductor or could you just size one conductor run with your primary circuit sized for the larger of either the equipment ground for that circuit or the GEC for the transformer.

No you cannot use one conductor to accomplish both purposes.
BTW the grounding electrode conductor will not be run in the same conduit with the circuit conductors for the primary feed.

 

[cpinetree]

From the way you asked both questions I am going to assume that the 480 primary originates in a MDP at or near the service location in this building. I think you are asking if the GEC from the SDS has to be a separate conductor or could you just size one conductor run with your primary circuit sized for the larger of either the equipment ground for that circuit or the GEC for the transformer.

No you cannot use one conductor to accomplish both purposes.
BTW the grounding electrode conductor will not be run in the same conduit with the circuit conductors for the primary feed.

Sorry if I am Hijacking this thread, but I have a similar install coming up in an all concrete building, where the transformer will be set 200' from the MDP (service entrance).
I can can drive a ground rod, so I guess that is OK? or should I run the 200' back to the mdp with my GEC, and then shouldn't I be connecting the new ground rod at the transformer back to the main service ground rods?

For what it is worth none of the other transformers in this building have ground rods driven or a GEC back to the MDP. What is my best course of action at these other locations to correct it.

 

[david]

You are only required to drive a ground rod when the transformer is out side

You are required to connect to a grounding electrode (system) near as possible (close) to the SDS.
If there is no grounding electrode part of the system in that location you must go to the closes one to that location.

 

[cpinetree]

You are only required to drive a ground rod when the transformer is out side

You are required to connect to a grounding electrode (system) near as possible (close) to the SDS.
If there is no grounding electrode part of the system in that location you must go to the closes one to that location.

Thanks.

 

[conmgt]

No you cannot use one conductor to accomplish both purposes.
BTW the grounding electrode conductor will not be run in the same conduit with the circuit conductors for the primary feed.

Can anyone expand on why one conductor couldn't/shouldn't be used to accomplish both purposes?
Can anyone expand on why the GEC can not be run in the same conduit as the transformer's primary conductors?

 

[kwired]

Can anyone expand on why one conductor couldn't/shouldn't be used to accomplish both purposes?
Can anyone expand on why the GEC can not be run in the same conduit as the transformer's primary conductors?

I would like to see any information on this also, just doesn't make any sense to me if the GEC and EGC are both running to the same point/ almost the same point.

 

[Smart $]

I would like to see any information on this also, just doesn't make any sense to me if the GEC and EGC are both running to the same point/ almost the same point.

New to 2011 NEC...

250.121 Use of Equipment Grounding Conductors. An
equipment grounding conductor shall not be used as a
grounding electrode conductor.

However, IMO this does not preclude using a GEC as a coincidental EGC. Fairly certain others disagree.