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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
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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.


  10. #10
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    Cool Re: generator to transfer switch to sub panel

    Quote Originally Posted by William Cline View Post
    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.
    Ok, been researching the web and I have a similar issue.

    I installed a Generac 100 amp transfer switch panel and a new 100 AMP sub panel and everything is wired and ready to go. All QO stuff!
    Now I need to move my needed 110 circuits into the new subpanel.

    My plan was to pigtail the circuits in the main panel and move them with the breakers to the new subpanel as the wires would be too short to do it any other way without extending the present wires.

    Can I just run one grounding conductor to the main panel grounding bar to the sub panel and can I just use the installed main panel grounding bar to do that. All other panels have separated grounding and grounded bars.

    Also the transfer and subpanels are properly wired back to the main panel. The generator appears to not have the ground bonded to the neutral.


  11. #11
    THOMAS HORNE's Avatar
    THOMAS HORNE Guest

    Default Re: generator to transfer switch to sub panel

    Quote Originally Posted by Garry Blankenship View Post
    Discussing gen sets, panels & transfer switches 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.
    The only case in which the neutral and Equipment Grounding Conductors of a premises wiring system are bonded together in a transfer switch enclosure is if the transfer switch is listed as and used as Service Equipment. In all other cases such a connection would violate the NEC. Using 2 interlocked circuit breakers located in the Service Equipment enclosure as the transfer switch is good example of the service equipment also being the transfer switch.

    In the installation being discussed there is one and only one place were the neutral and Equipment Grounding Conductor are connected to each other in the premise wiring system. That 1 place is in the Service Equipment enclosure. If the neutral from the generator is insulated from the generator's frame and from contact with other conductive paths to ground, then for the situation described a 2 pole transfer switch would be all that is required. The optional standby load panel would be a feeder supplied panel (Sub Panel) regardless of which source was supplying the panel. There would be no bonding jumper in the Sub Panel.

    If the Neutral of the generator is connected to ground anywhere other than the Service Equipment enclosure then the neutral of the generator would have to be switched by the same mechanism which switches the 2 energized conductors. That would make the generator a Derived System. The optional standby load panel would be installed just as if it were Service Equipment. It would have a main bonding jumper and a Grounding Electrode Conductor to a Grounding Electrode System.

    If the generator is outdoors then it would also have to have a Grounding Electrode System connected to the neutral at the generator and the neutral would have to be bonded to the frame of the generator as well.

    --
    Tom Horne


  12. #12
    THOMAS HORNE's Avatar
    THOMAS HORNE Guest

    Default Re: generator to transfer switch to sub panel

    Quote Originally Posted by earl simpson View Post
    Ok, been researching the web and I have a similar issue.

    I installed a Generac 100 amp transfer switch panel and a new 100 AMP sub panel and everything is wired and ready to go. All QO stuff!
    Now I need to move my needed 110 circuits into the new sub panel.

    My plan was to pigtail the circuits in the main panel and move them with the breakers to the new sub panel as the wires would be too short to do it any other way without extending the present wires.

    Can I just run one grounding conductor to the main panel grounding bar to the sub panel and can I just use the installed main panel grounding bar to do that. All other panels have separated grounding and grounded bars.

    Also the transfer and sub panels are properly wired back to the main panel. The generator appears to not have the ground bonded to the neutral.
    The answer you your question in paragraph 3 of your posting depends on what you mean by "grounding conductor." which of the busbars in the sub panel are you connecting back to the main panel? Is it the busbar which is insulated from the sub panel's cabinet? Or is it the busbar which is mounted directly to the cabinet metal to metal?

    If you mean the Equipment Grounding Conductor (EGC) busbar that is screwed right into the sub panel cabinet with metal on metal screws then you would size that for circuit breaker in the Service Equipment enclosure which supplies one set of the transfer switches supply conductors.

    I take it that you are not going to run the EGCs nor the Grounded Current Carrying Conductors (Neutrals) of the circuits that you are moving to the sub panel? By this I mean that the only conductors which you plan to move are the Energized Conductors of the moved circuits.

    Does the Generac transfer switch transfer the main lug connections of the sub panel from a breaker in the Service Equipment enclosure to the energized conductors from the generator?

    Any chance that you could take a picture of the whole assembly with the covers removed? I mean 1 picture which shows all three enclosures at once. Additional pictures of the individual enclosures with their covers removed wouldn't hurt but the one that shows all three will make it easy to see the connections between all three.

    --
    Tom Horne


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