Added transformer grounding

[raymacaluso]

I have an existing 2000A 480V 3PH switchgear on site.
This is in a basement of existing high school.
This switchgear is grounded by ground rods, building steel and cold water pipe means.
Thus I have come from switchgear and installed a 480V 3Phase 200A 4W panel. From that panel I have installed a 45KVA 480V Pri/208V sec transformer. Which is the feeding a 208V 125A PH 5W panel
I used for grounding purpose for the transformer a ground rod installed in the concrete floor. Inspector is telling me that I have to ground to cold water pipe and then run wire outside and install (2) ground rods to ground this transformer.
I am confused this seems overkill if I already have a ground system in place at the switch gear.
Am I correct in this and should take this issue with the Chief electrical inspector?

 

[iwire]

Re: Added transformer grounding

The grounding electrodes at the service have nothing to do with your separately derived system.

You are required by 250.30(A)(4) to connect this SDS to a grounding electrode consisting of either building steel or a water pipe. If either of those are not available you have to install another type of electrode.

That covers the grounding electrode system of this SDS, there are also bonding requirements in 250.104(A)(4).

You should really read all of 250.30 and 250.104(A)(4).

The only thing I see wrong in the inspectors request is the additional ground rods if building steel or water lines are available.

 

[petersonra]

Re: Added transformer grounding

why can't he just tap off the existing GEC?

 

[iwire]

Re: Added transformer grounding

Originally posted by petersonra:
why can't he just tap off the existing GEC?

Did you read 250.30 and 250.104?

He may be able to do that if if follows the rules in 250.30(A)(3).

The grounding rod driven into the ground he has now will not do anything.

In my mind a better question is why the SDS can not use a properly sized EGC to connect the XO back to the service grounding electrode system?

I believe Don has put in proposals to do that.

 

[petersonra]

Re: Added transformer grounding

Originally posted by iwire:

Originally posted by petersonra:
why can't he just tap off the existing GEC?

Did you read 250.30 and 250.104?

He may be able to do that if if follows the rules in 250.30(A)(3).

Bob: I don't see any rule he has to worry about other than making the connection in one of the specified ways.

The grounding rod driven into the ground he has now will not do anything.

Bob: Don't all GEs in the same building have to be bonded together?

In my mind a better question is why the SDS can not use a properly sized EGC to connect the XO back to the service grounding electrode system?

Bob: A good question. In fact this is a common practice for industrial machinery.

I believe Don has put in proposals to do that.

[ May 12, 2005, 02:51 PM: Message edited by: petersonra ]

 

[bob]

Re: Added transformer grounding

Iwire said

In my mind a better question is why the SDS can not use a properly sized EGC to connect the XO back to the service grounding electrode system?

I agree. Since there is an EGC connected to the frame of the transformer and the XO is strapped to the frame, is not that the same thing?