Bonding transformers

[DrSparks]

Quick question. I'm installing a 100kva 480-208 transformer on a new 1200A 480v service to serve existing lighting and 120v receps. The primary overcurrent device will originate from the mdp and the secondary will connect to a 200A main breaker panel. Since it's a separately derived system, i know i need a GEC to the water main. My question is, does the GEC for the mdp and the GEC for the SDS need to be bonded at some point? Also, does the SDS need a supplemental grounding electrode such as ground rods?

 

[George Stolz]

The grounding requirements are in 250.30(A)(4). Since the service is required to be connected to the metal water pipe electrode, and your SDS will be connected to it, then the two GECs can't help but connect together by virtue of being connected to the same electrode.

The water pipe will already be supplemented by either a concrete encased electrode, ground rod, or other electrode by following 250 Part III when grounding the service. No additional efforts required.

I would be strongly inclined to catch steel instead to interconnect the electrodes and systems, if practical.

Welcome to the forum!

 

[DrSparks]

Thanks

Thanks

The grounding requirements are in 250.30(A)(4). Since the service is required to be connected to the metal water pipe electrode, and your SDS will be connected to it, then the two GECs can't help but connect together by virtue of being connected to the same electrode.The water pipe will already be supplemented by either a concrete encased electrode, ground rod, or other electrode by following 250 Part III when grounding the service. No additional efforts required.I would be strongly inclined to catch steel instead to interconnect the electrodes and systems, if practical.Welcome to the forum!

thanks George. You answered my question beautifully. Another question: do i need a separate GEC to the water main or can i simply tap off the mdp's GEC which will be a much larger conductor? Like a split-bolt connection... Btw, i love Groundskeeper Willy! Lol

 

[George Stolz]

Do i need a separate GEC to the water main or can i simply tap off the mdp's GEC which will be a much larger conductor? Like a split-bolt connection...

Yes you can tap, but not using a split bolt. 250.64(D)(1) and/or 250.30(A)(6)(c), depending on the particulars of your installation.

 

[don_resqcapt19]

Yes you can tap, but not using a split bolt. 250.64(D)(1) and/or 250.30(A)(6)(c), depending on the particulars of your installation.

Why can't you use a split bolt for this purpose?

 

[xformer]

Why can't you use a split bolt for this purpose?

My guess is that split bolt is not rated for grounding... or direct burial...

 

[George Stolz]

Is a split bolt listed for grounding/bonding?

 

[don_resqcapt19]

Is a split bolt listed for grounding/bonding?

Some are listed to both UL 467 and UL 486. 467 is for bonding and grounding.

http://www.harger.com/products/idx.cfm?subc3id=104&p=1&thid=682&footid=0&footinfoid=0&oiid=817

 

[George Stolz]

Cool! Those would be compliant.

 

[don_resqcapt19]

My guess is that split bolt is not rated for grounding... or direct burial...

This one I don't understand. It is listed for direct burial but not for grounding and bonding???


Note, I believe that the UL standard in the document is a typo...there is no UL 468, wire connectors are UL 486.