Generator system ground vs chassis ground

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Bigwooo
Bigwooo Solar Expert Posts: 62 ✭✭
I'm installing a new Generac generator as backup to my solar. Thanks to some suggestions from this site I've worked out most of the wiring, however I have one more question about grounding:

The generator has two grounds: (1) The ground that runs with the hot/neutral, and (2) A ground lug that is attached to the outside of the enclosure. I checked the ground lug on the outside of the enclosure and it's tied to the system ground that runs with the hot and neutral.


I plan to connect the system ground to the main ground buss, however what should I do with the external ground lug?

Should that also be connected directly to the main ground buss?

Should I ignore it since the enclosure is tied to the main ground anyway?

Or...should I connect it to my ground rod that is bonded back to the main ground buss?

(Note: Ground and neutral are NOT tied together in the generator, they are only bonded at the main panel)

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: Generator system ground vs chassis ground

    Towards the end of this thread is a very nice discussion of proper generator grounding.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Bigwooo
    Bigwooo Solar Expert Posts: 62 ✭✭
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    Re: Generator system ground vs chassis ground
    BB. wrote: »
    Towards the end of this thread is a very nice discussion of proper generator grounding.

    -Bill

    Thank you for the link. I knew that thread was out there, but couldn't come up with it in the search. Looks like "yes" I do ground the chassis of the generator to the main ground rod, which fortunately for me is located next to the generator .
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
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    Re: Generator system ground vs chassis ground
    Bigwooo wrote: »
    I'm installing a new Generac generator as backup to my solar. Thanks to some suggestions from this site I've worked out most of the wiring, however I have one more question about grounding:

    The generator has two grounds: (1) The ground that runs with the hot/neutral, and (2) A ground lug that is attached to the outside of the enclosure. I checked the ground lug on the outside of the enclosure and it's tied to the system ground that runs with the hot and neutral.


    I plan to connect the system ground to the main ground buss, however what should I do with the external ground lug?

    Nothing - it's not needed if the generator frame is tied to the building grounding system via an adequately sized equipment grounding conductor (the ground that runs alongside the hot/neutral).

    Should that also be connected directly to the main ground buss?

    No. Since it's tied to the equipment grounding conductor that runs with the hot/neutral, as soon as you connect that equipment grounding conductor in the panel then it will *already* be connected to the main ground bus.

    Should I ignore it since the enclosure is tied to the main ground anyway?

    Yup.

    Or...should I connect it to my ground rod that is bonded back to the main ground buss?

    No need. As the green wire is already tied to the frame, as soon as you connect that green wire to the panel ground bus - which is tied to the ground rod - then the frame will be tied to the ground rod.

    (Note: Ground and neutral are NOT tied together in the generator, they are only bonded at the main panel)

    That's the key issue. The other issue is simply making sure that the equipment grounding conductor is big enough.

    In the Baja example there was high-resistance soil so it's best to use two ground rods and so *in that case*, since I would have to bridge the two ground rods anyway, I just put the second rod at the gen and end the solid copper wire run at the frame of the gen.

    But it doesn't *have* to be a big, fat, TOUGH (because it's probably direct buried in sand) solid copper wire. if you are running hot/neutral/ground through a conduit together and the ground wire is the correct size, then that's good enough and no external grounding of the frame is needed.

    [EDIT: In fact, now that I think about it - if that ground (the one run with the hot/neutral) is tied to the frame inside the generator, then it's probably best to NOT do an external grounding as well because of a potential "ground looping" issue. I have to leave it to the engineers to figure that one out though. From the installer POV - if the frame is grounded by that green wire, then I would NOT ground the frame to the ground rod as well.]
  • Bigwooo
    Bigwooo Solar Expert Posts: 62 ✭✭
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    Re: Generator system ground vs chassis ground

    Wow DWH great post...thank you. I was returning to update those that commented on my installation. After reading your post, I removed the chassis ground that I had bonded to the ground rod. I've followed all your suggestions and things appear to be running great. Although the Generac is a bit louder than I anticipated, it seems to be a decent generator...time will tell. Some of my other neighbors down here have them and have had good luck. My fingers are crossed.

    Now that the generator's in and functioning, I can use it to keep my batteries charged for however many days it's going to take me to upgrade my solar. I'm going from 4 panels to 14 along with all the other components that go with the upgrade. Looking forward to having more power.
  • bobdog
    bobdog Solar Expert Posts: 192 ✭✭
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    Re: Generator system ground vs chassis ground

    Just a note on the Generac gp5000. I spoke with technical services at Generac and they told me the neutral IS bonded to the ground on the generator. And if I was to use it to power my house, that I would have to disconnect it at the generator.

    I assume this is due to the house (cabin) already having a neutral/ground bond.

    Bigwooo, How did you disconnect the neutral bond from the ground?

    Tim