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  1. #1
    Jim Donofrio's Avatar
    Jim Donofrio Guest

    Default generator to transfer switch to sub panel

    Greetings,
    In connecting a generator to a sub panel can the neutral and ground from the generator go to the main panel or must the sub panel have its own ground seperate fro the main panel.?

    So, two hots a neautral and grond from a generator first go to a (break first) transfer switch . Also two hots and a neutral and a ground to the same (break first) transfere switch. Then coming from the transfer switch will be the two hots neuatral and ground to the sub panel.

    The only thing that would be switched back and forth would be the hots.
    Is this code, id this correct is this the best way
    Thank you in advance.

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  2. #2
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    Default Re: generator to transfer switch to sub panel

    Jim,
    The hots, neutral and ground from the generator must be in the same conduit to the transfer switch.


  3. #3
    Jim Donofrio's Avatar
    Jim Donofrio Guest

    Smile Re: generator to transfer switch to sub panel

    William cline,
    I understand that part of it. My question is does the sub panel require its own neutral and ground seperate from the main panel (sub not tied to main).

    If the power is returned to the main panel while the generator is still running, then the neutral and grounds are recieving possible current from two sources. ( I understand how the transfer switch works) Also, even if no power from company it is still sharing neutrals and grounds with other sub panels and the main.

    If I have ground rod driven for the sub and run all current despite its source from the seperate ground in the sub.Then is it stoll code to tie my neutral to the ground. Opposed to going back to the pole?
    What is the code on this?


  4. #4
    Garry Blankenship's Avatar
    Garry Blankenship Guest

    Default Re: generator to transfer switch to sub panel

    Discussing gen sets, panels & transfer switchs is like giving verbal driving directions through a network of logging roads - - - words often get in the way rather than serve. If I understand your question, my answer would be both. A transfer switch should have three major supplies; one from the main panel, one from the generator and one to the emergency power panel. Each supply should have a full compliment of hots, ( 240 volts most likely ), a neutral and a ground. All will terminate in their appropriate place in the transfer switch, ( all neutrals together, all grounds together and the hots in their respective xfr sw locations ). Effectively, the neutrals and grounds are spliced together in the xfr. sw. and the hots are in their switch locations.


  5. #5
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    Thumbs up Re: generator to transfer switch to sub panel

    Jim,
    In 250.24(5) of the NEC, there is to be no load side of the service disconnect (meter main) connection between the equipment grounding conductor and the grounded conductor (neutral). This interconnection only takes place in the main service disconnect panel (service entrance or main). The neutral bar is to be isolated from the panel case and the equipment grounding conductor in the sub panels. The interconnection at the transfer switch would be considered at the supply side of the generator, therefore permissible (by my interpretation). Those two places are the only ones where you should have a connection between the equipment ground and the grounded conductor (neutral). The extra ground rod is not a problem if connected to the other grounding electrodes thru the grounding electrode conductor running between all of your panels and the transfer switch panel.
    Hope I got that all right and comprehensible.


  6. #6
    Jim Donofrio's Avatar
    Jim Donofrio Guest

    Default Re: generator to transfer switch to sub panel

    William thank you for the info. What appears confusing is that a stand by generator is getting its ground from a transfer switch that is not grounded.

    If the generator is getting its grounding from the sub panel and the sub is gettining it from the main then even though you have a break first switch the switch box could still be energized if shorted. This would carry to the sub and the main. There is no true isolation. Shouldnt a generator be treated as a seperate source and have its own ground grounding bar and earth rod?


  7. #7
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    Default Re: generator to transfer switch to sub panel

    Hi Jim,
    I do not sense that I am clarifying this properly. Each and every panel is grounded thru the equipment grounding conductors that run from the main to each of the sub panels and the transfer switch and the generator. Thus all metal cabinets and the generator frame are connected. Then the equipment grounding conductor connects with the electrode grounding conductor (to the ground rod) and the grounded conductor (neutral) at the main ground/neutral bar and hence every cabinet is connected to the ground rod (grounded). You can connect another ground rod to the equipment grounding conductor at the sub, but not to the neutral at that point.


  8. #8
    Jim Donofrio's Avatar
    Jim Donofrio Guest

    Default Re: generator to transfer switch to sub panel

    So, what you are saying is that it is ok for all components to share the same ground/neutral tie in?

    Stand by generators need to get ground from somewhere. If the Generator neuatral and ground are tied together at the transfer switch then this is ok!

    because the transfere switch is tied to the sub panel and the sub is tied to the main and the main is tied to a house pipe.

    So the path to ground is Gen to Transfer to sub to main to water pipe.

    No component needs a seperate ground rod to earth? What would happen in the event the city side shorts to ground, then this would make live the generator frame? am I incorrect.

    I appreciate your patience


  9. #9
    Join Date
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    Default Re: generator to transfer switch to sub panel

    All the panels share the same ground wire (equipment), the sub panel does not have a connection between the neutral and equipment grounding conductor in the cabinet. The interconnections between neutral and equipment ground are allowed with in the cabinet containing the disconnect for the service, I.e. the service entrance for the utility and the transfer switch for the generator, unless you have another disconnect for the generator prior to the transfer switch, in which case, the interconnection would be there.
    A short to ground on the utility side would trip the over current device at the drop, a short after the main disconnect would trip the main, and a short at the generator side service would trip the generators over current device.
    In any case the current would be running to ground thru the equipment/electrode ground path to a house pipe? Is there no original ground rod? You are permitted more ground rods as long as they are tied together with the equipment/electrode grounding wire system. Do not tie the neutral to the equipment grounding conductor with in the sub panel.


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