Code question on generator grounding

Posted by on September 7, 2008, 10:05 pm

On Sun, 7 Sep 2008 18:34:22 -0700 (PDT), misterjustme@gmail.com wrote:

>Grounding and bonding depend on whether or not is a seperatley derived
>system or not. I assume you are permanantly mounting the generator
>and it is not a portable unit. I also assume you are installing a
>transfer switch. Is this correct? NEC 2005 Article 250 is where to
>look.

It is a permanent installation. I will not be using a transfer switch. I
will be backfeeding the panel through one of the breakers. That breaker
has a mechanical interlock which prevents both it and the main breaker
being on at the same time. (It is impossible to turn on the backfeed
breaker on unless the main is off, and impossible to turn the main breaker
on unless the backfeed breaker is off.)

Thanks for the code reference.

Posted by on September 8, 2008, 12:47 am

On Sun, 07 Sep 2008 22:05:03 -0400, NoSpam@aol.com wrote:

>On Sun, 7 Sep 2008 18:34:22 -0700 (PDT), misterjustme@gmail.com wrote:

>>Grounding and bonding depend on whether or not is a seperatley derived
>>system or not. I assume you are permanantly mounting the generator
>>and it is not a portable unit. I also assume you are installing a
>>transfer switch. Is this correct? NEC 2005 Article 250 is where to
>>look.

>It is a permanent installation. I will not be using a transfer switch. I
>will be backfeeding the panel through one of the breakers. That breaker
>has a mechanical interlock which prevents both it and the main breaker
>being on at the same time. (It is impossible to turn on the backfeed
>breaker on unless the main is off, and impossible to turn the main breaker
>on unless the backfeed breaker is off.)
>Thanks for the code reference.

OK that is what we needed to know. That is not a separaate;y derived
system, you want to remove the jumper between the ground and the
neutral in the generator. You still run a green wire ground between
the generator and your house grounding system. A rod is not needed

Posted by Caesar Romano on September 8, 2008, 8:38 am

On Sun, 07 Sep 2008 22:05:03 -0400, NoSpam@aol.com wrote Re Re: Code
question on generator grounding:

>That breaker
>has a mechanical interlock which prevents both it and the main breaker
>being on at the same time. (It is impossible to turn on the backfeed
>breaker on unless the main is off, and impossible to turn the main breaker
>on unless the backfeed breaker is off.)

Where do you get such an interlock? Do you have a product name &
manufacturer? Even better, do you have a link?

Thanks

Posted by HeyBub on September 8, 2008, 10:54 am

Caesar Romano wrote:

> On Sun, 07 Sep 2008 22:05:03 -0400, NoSpam@aol.com wrote Re Re: Code
> question on generator grounding:

>> That breaker
>> has a mechanical interlock which prevents both it and the main
>> breaker being on at the same time. (It is impossible to turn on the
>> backfeed breaker on unless the main is off, and impossible to turn
>> the main breaker on unless the backfeed breaker is off.)

> Where do you get such an interlock? Do you have a product name &
> manufacturer? Even better, do you have a link?

They differ by panel model within manufacturer and are all hideously
expensive. Here's what I did on a Square D panel.

The connection to the generator goes to a double circuit breaker located in
the upper right column. For normal, non-emergency, operation, this breaker
is OFF.

It's possible to fashion a metal or plexiglass plate that nudges against
both the main circuit switch and this odd circuit breaker. This plate is
bolted to the panel cover via elongated holes in the plate that allow the
plate to slide, making contact with the two switch handles. The trick is to
match the sliding with the positions of the main switch and the odd breaker.
The breaker can't be turned ON unless the main switch is OFF. The main
switch can't be turned ON unless the breaker is OFF.

On a Square D, main switch ON is to the right and circuit breaker OFF is to
the right. If you have a block plate between the levers, it's obvious the
circuit breaker can't be moved to the left (ON) unless the main is first
moved to the left (OFF) and the blocking plate moved likewise. Similarily,
the main can't be moved right (ON) unless the circuit breaker is first moved
right (OFF) and the blocking plate scooted over with it.

Get the model and make of your panel and do a search on "
interlock" The results will give you an idea of how the manufacturer of your
panel wants the thing to work. You can then either find the best price on
the "approved" device or, as I did, fashion your own.

Posted by Caesar Romano on September 8, 2008, 11:31 am

wrote Re Re: Code question on generator grounding:

>Get the model and make of your panel and do a search on "
>interlock" The results will give you an idea of how the manufacturer of your
>panel wants the thing to work. You can then either find the best price on
>the "approved" device or, as I did, fashion your own.

Thanks for the detailed description. I can easily visualize the
"field" modification that you made. Very creative. Nice going.

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Code question on generator grounding - Page 4