Optional standby system

[kevinware]

I am an apprentice who is in need of clarification. I recently installed a Square "D" portable generator panel (QO48M30DSGP) on my single family dwelling. I had my lead man come over and check my work and I was informed I was in violation of the NEC because I should have installed my generator panel as a separate services panel and driven a separate ground rod. The way I have it installed is this: from my main service panel I have a 30 amp two pole breaker back-feeding a 30 Amp two pole breaker located in the generator panel. The generator is back-feeding another 30 amp two pole breaker in the same panel. The two 30 amp two pole breakers are mechanically interlocked and thus I thought I had a manual transfer switch. The grounded (white) wire from the generator flanged inlet is run to a grounded bus inside the generator panel. And the grounding (green) wire from the generator flanged inlet is run to a E.Q. bus inside the generator panel and back to the service panel. The buses inside the generator panel are not bonded together. The grounded bus of the generator panel and the grounded bus of the service are solidly connected (no break when transfer happens) and there is a main bonding jumper installed in the service panel. My lead man said this can be a potentially dangerous installation in that I am putting current on the utility's grounded wire coming into my house. I am trying to find in the NEC an article telling I need to open the grounded (white) wire. I am not trying to disrespect my lead man, I am just trying to understand. To my understanding article 100 does not define my setup as a "separately derived system" and I really can't find a reference that says I am illegal. Unless the statement in article 702.6 stating "inadvertent interconnection of normal and alternate sources of supply in any operation of the transfer equipment". If my setup in unsafe then why does article 702.10(B) state: "Where a portable optional standby source is used as a nonseparately derived system, the equipment grounding conductor shall be bonded to the system grounding electrode". Is this situation one of those "article 90.4" I keep hearing about?

Thanks for all your help,

Kevin

 

[ron]

Re: Optional standby system

Sounds ok to me. Since the neutrals for both sources are solidly connected, be sure the neutral to ground bond in the generator is removed (if it was present), since it is not a separately derived source.

 

[tom baker]

Re: Optional standby system

you are correct and your lead man is wrong. If the transfer switch (circuit breakers in your case) does not transfer the neutral then it is not a seperatly derived system, however a netral to case connection in the generator must not be made. The code section is in article 250 on seperatly derived systems which I think is 250.32 I don't have my code book. Only when the neutral is transferred is the generator required to have a grounding electrode system.

 

[kiloamp7]

Re: Optional standby system

ron's 2nd sentence is correct.

tom baker's 2nd sentence is correct.

This is not a separately derived system. The neutral of the generator source should not be directly connected to a grounding electrode (earth) nor bonded to equipment ground (enclosures, etc.) but should be solidly connected to the neutral (grounded conductor) of the utility source.

The utility source should be bonded & grounded in the conventional way it is normally done.

End result is a utility source- to- generator source manual transfer switch with neutrals of the two systems unswitched.