Step-Down Transformer Grounding/Bonding

[RandyFL73]

I have a situation where we have a 480/208V step-down transformer within a tenant space that has no available building steel or metal pipe for grounding/bonding. The main service ground bus is 300ft. away. We are considering driving a ground rod for connection to ground however, there are several of these spaces that will require the same grounding scenario in this building. Code allows the use of a ground rod when there is no building steel or metal water pipe available. The question is, would it be better to ground multiple transformers to one ground rod or drive individual ground rods for each transformer?

 

[jumper]

I believe you are misinterpreting 250.30(A)(4).

That exception does not allow what you trying to do.

You cannot just put in a rod and call it good. You must tie them all into the building GES.

You can drive auxiliary rods, but that does not relieve you from still connecting everything together somehow. The exception merely says that if building steel or water is not available you can tie into an alternative electrode that is part of the GES.

You may not go solo and have different GESs in one structure.

 

[RandyFL73]

I was referring to 250.30(A)(4) Exception 1, 250.52(A) and 250.53. This is a bit of an oddity and a first for me.

 

[RandyFL73]

Perhaps I am, I was referring to 250.30(A)(4) Exception #1 and also 250.52 and 250.53.

 

[jumper]

Perhaps I am, I was referring to 250.30(A)(4) Exception #1 and also 250.52 and 250.53.

Read the first sentence of 250.50.

 

[jumper]

Thread on the topic.

http://forums.mikeholt.com/showthread.php?t=162742

 

[RandyFL73]

I agree. This is a first and trying to think through some options. They all stop with GES.

 

[RandyFL73]

So it looks like the best solution is to run a common GEC back to the main and tap off of it for each xfmr.

 

[jumper]

So it looks like the best solution is to run a common GEC back to the main and tap off of it for each xfmr.

It is a common solution.