Grounding of generators

[sbutler]

Please tell me if I am interpreting the code correctly. When using a 3-pole ATS, a ground rod is not required (nor desired) at the generator as the neutral is not being switched and is sharing the neutral from normal power. Doing so could create a ground loop. On 4-poles switches with the neutral being switched, a ground rod is required as this is a seperatly derived system.

Thanks to any and all replies.

 

[SG-1]

I agree with your interpretation.
A sign is generally required at the Service disconnect, warning the operator there is a second source. Section 708.(B),701.9(B) & 702.8(B).

 

[steve66]

I disagree.

With a 3 pole switch, you don't want a neutral to ground bond at the generator. But (assuming its an outdoor generator) you can (and should) drive a ground rod at the generator set, and connect that to the generators frame. Just don't connect it to the neutral at the generator.

 

[dbuckley]

But (assuming its an outdoor generator) you can (and should) drive a ground rod at the generator set...

Is that based on a code compunction, or just a preference for installing a supplemental grounding rod?

 

[jwelectric]

Is that based on a code compunction, or just a preference for installing a supplemental grounding rod?

With some generators it would be a requirement of 110.3(B)

 

[ceb58]

Please tell me if I am interpreting the code correctly. When using a 3-pole ATS, a ground rod is not required (nor desired) at the generator as the neutral is not being switched and is sharing the neutral from normal power. Doing so could create a ground loop. On 4-poles switches with the neutral being switched, a ground rod is required as this is a seperatly derived system.

Thanks to any and all replies.

Correct on a three phase system. If it were single phase then you would have a 2 pole switch for a non-separately derived system.

With some generators it would be a requirement of 110.3(B)

Generac is a prime example.

 

[PaulWDent]

I disagree.

With a 3 pole switch, you don't want a neutral to ground bond at the generator. But (assuming its an outdoor generator) you can (and should) drive a ground rod at the generator set, and connect that to the generators frame. Just don't connect it to the neutral at the generator.

I guess you mean "with a two-pole switch". If it was a 3-pole switch, the neutral and both hot legs would be switched, and the generator neutral should then be grounded at the generator.

I have the same issue with a photovoltaic/battery/inverter installation. I have a two-pole service changeover switch (both hot legs) from utility to solar, so neutral is not being switched; therefore neutral should not be grounded at the inverter, becaue it is getting its ground via the utility neutral to which it is permanently connected.

 

[mtfallsmikey]

I disagree.

With a 3 pole switch, you don't want a neutral to ground bond at the generator. But (assuming its an outdoor generator) you can (and should) drive a ground rod at the generator set, and connect that to the generators frame. Just don't connect it to the neutral at the generator.

Is it preferable to use a ground rod, or tie into the panel/building ground, or both??

 

[steve66]

Is that based on a code compunction, or just a preference for installing a supplemental grounding rod?

I'm basing that on the generator being a separate "structure", and 250.50. So just like a detached garage needs its own grounding electrode, an outdoor generator would also need one.

I guess you mean "with a two-pole switch". If it was a 3-pole switch, the neutral and both hot legs would be switched, and the generator neutral should then be grounded at the generator.

As CEB58 mentioned, when I said a 3 pole switch, I was thinking of a three phase system and a switch for the 3 hot wires.

Steve

 

[steve66]

Is it preferable to use a ground rod, or tie into the panel/building ground, or both??

Here are the two options as shown in the handbook.

http://i568.photobucket.com/albums/ss124/myphotobucket2221/GroundingOptions.jpg


IMO, in most cases it is easier and makes more sense to not switch the neutral, and wire it like the first diagram. Notice that they don't show a ground rod at the generator, but they could be showing an indoor generator. If a ground rod is added at the generator, it would be connected to the ground or frame. It wouldn't have any connection to the the neutral or the center of the wye at the generator.

The first diagram shows no bond between the Neutral and ground at the generator. I sometimes wonder if some generators aren't provided with this bond already in place. If that were the case, it would have to be removed.

Sometimes the bottom setup is needed. An example might be when a generator feeds multiple buildings. But I typically wouldn't use a 4 pole switch unless I had a good reason to.