Grounding seperately derived system

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mikehughes8

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I have a 3 Phase / 4 wire service with a feeder connecting to a 208 / 480 (delta / wye) transformer. This Transformer feeds a 100A Panel. Since this is a seperately derived system..am I ok to bond only at the 100A panel and not the source (transformer).
Secondly, a grounding electrode was driven at the source and another electrode was driven at the 100A panel. There is not a bond connecting these electrodes. However, it would seem to me that they are electrically connected via the EGC. With the electrical connection made via the EGC does this qualify as a grounding electrode system and cover me when trying to meet requirements of 250.56? i.e supplemental ground rod when trying to meet 25 ohm requirements.

Thanks...hope that wasn't to confusing.
 
mikehughes8 said:
I have a 3 Phase / 4 wire service with a feeder connecting to a 208 / 480 (delta / wye) transformer. This Transformer feeds a 100A Panel. Since this is a seperately derived system..am I ok to bond only at the 100A panel and not the source (transformer).
Secondly, a grounding electrode was driven at the source and another electrode was driven at the 100A panel. There is not a bond connecting these electrodes. However, it would seem to me that they are electrically connected via the EGC. With the electrical connection made via the EGC does this qualify as a grounding electrode system and cover me when trying to meet requirements of 250.56? i.e supplemental ground rod when trying to meet 25 ohm requirements.

Thanks...hope that wasn't to confusing.
Click to expand...

250.30(A)(1) allows you to bond the SDS at any point between the SDS and the first disconnect or OCPD.

Confused a little about using the EGC to bond the electrodes. I'll let someone else chime in while I figure on it...
 
Secondly, a grounding electrode was driven at the source and another electrode was driven at the 100A panel. There is not a bond connecting these electrodes. However, it would seem to me that they are electrically connected via the EGC. With the electrical connection made via the EGC does this qualify as a grounding electrode system and cover me when trying to meet requirements of 250.56? i.e supplemental ground rod when trying to meet 25 ohm requirements.
Click to expand...

You might be able to use the EGC as a GEC but here are some questions that must be answered.

What size is the EGC between the service disconnecting means and the rod at the transformer?

Does the EGC meet the 250.64(E)?

As a side note, there is a proposed change for the 2011 NEC to prohibit a EGC to also be used as a GEC.

Chris
 
raider1 said:
You might be able to use the EGC as a GEC but here are some questions that must be answered.

What size is the EGC between the service disconnecting means and the rod at the transformer?

Does the EGC meet the 250.64(E)?

As a side note, there is a proposed change for the 2011 NEC to prohibit a EGC to also be used as a GEC.

Chris
Click to expand...

EGC is a #6 and it is electrically continuous This whole issue begs the question:

If there is a proposal to eliminate use of the EGC as a GEC is there also a proposal to eliminate use of a GEC as an EGC. I don't see a significant difference and it seems as though they both can double for the other.
 
mikehughes8 said:
EGC is a #6 and it is electrically continuous This whole issue begs the question:

If there is a proposal to eliminate use of the EGC as a GEC is there also a proposal to eliminate use of a GEC as an EGC. I don't see a significant difference and it seems as though they both can double for the other.
Click to expand...

I just re-read the proposal and it prohibits the GEC to be used as an EGC.

Chris
 
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