ECN Forum Forums Code Related Discussion NEC & other Code issues SDS in Garage

George Little Member posted 02-16-2005 04:06 PM George
No matter how many wires you use in the derived system's supply conductors to the house you still have to avoid re grounding the service supplied feeder neutral that runs from the Service Equipment to the Emergency Panel in the house. There are two ways to avoid this. One is to use a three pole switch so that the required grounding electrode conductor to your building disconnecting means; in this case the transfer switch; is not bonded to the service supplied feeder's neutral. The other would be to not bond the derived system neutral to the building disconnecting means. Remedy two is not available to you because you ran only three conductors from your derived system. You have to bond the derived system neutral to ground at the house as required in 250.32 (B) (2). If the generator does not supply any load, including any receptacles on the generator itself, at the garage then you can argue that 250.32 does not apply. You can also argue that it does not apply because the generator is not a service. But if you look at how transformers located outdoors are treated by 250.24 Grounding Service-Supplied Alternating-Current Systems, (A) System Grounding, (2) Outdoor Transformer, you will see that the intent of the code is to bond the neutral of the supply to buildings both at the outdoor source and at the disconnecting means. I guess my point is that if you are going to apply the rules for two or more buildings... to a derived system then you should apply them consistently.
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Tom H

George
Is there actually no electrical supply to the detached garage from the service in the house? If there is any supply to the garage from the houses service then the derived system conductors are a metallic pathway in parrallel with that branch circuit or feeder and the branch circuit or feeder is a metallic pathway between the two buildings for the purpose of the wiring of the derived system.
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Tom H

Bingo! You are 100% on target Tom. Which goes to show that the inspector (me) is not always correct. This was a point that I had not considered. Thanks for your input and others on this page.

Changing the rules now huh?
You originally said no metallic paths. ;-)

Yah, got to do something sometimes to see if you are paying attention.

I assumed this was a "test" question.
If the generator is the sole source of power to the shed and serves loads there, the house is the second building.