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  1. #1
    Steve Boyer's Avatar
    Steve Boyer Guest

    Default Generator subpanel...??

    I have not seen a generator panel quite like this. I asked three different electrician acquaintances about it and got three different answers. I guess for a few years this type of installation was allowed, but not any more. Seems to me there should be a separate grounding bar in there some place, but I do not know how that would work with the generator energized and operating. There are obvious double wires on the neutral bar that was a no brainer, but the doubled inbound neutrals...one from the main panel (fed by a 50 amp 240 breaker) and one from the generator line. There is a main gang breaker at the top to switch from the service panel to the generator so no backfeed is possible. There was #6 three wire coming from the service panel and #4 4 wire coming from the generator. The generator 4th wire/ground was tied to the neutral bar. The owner said a permit was pulled and an electrician installed it, but he was also told that soon after it was no longer allowed. This installation is beyond my basic knowledge. I can see that it would work fine, but would not be sure how it would react with a ground fault in one of the subpanels branch circuits during generator use...

    My guess is that a separate ground bar with the generators ground going to it plus all the branch grounds tied to the main panels ground bar would do the trick... Any thoughts?

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  2. #2
    James Duffin's Avatar
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    Default Re: Generator subpanel...??

    IMO...the generator panel is a sub-panel and needs a 4-wire feeder from the main service panel and the generator set. Unless you installed a 4-pole transfer switch I don't see a way to isolate the neutrals and grounds when used with the PC or generator.


  3. #3
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    Default Re: Generator subpanel...??

    (Sigh.)

    If you guys would not insist on using the term "sub" in front of panel I suspect that you would realize that is a manual transfer switch/emergency power service equipment panel (especially James and I believe James says he is an electrician).

    The top right breaker is (apparently, although this was not stated) fed from the service equipment panel to the left. Therein lies a problem in that the service equipment to the left is, under normal utility operating conditions, the service equipment and therefore the grounds in this panel (for right now I will just call this a "panel" and not call this "manual transfer switch/emergency power service equipment panel" as that implies it is "service equipment", which it is under one operating condition, but not under the other operating condition).

    Under normal utility power, this panel would be (I suspect, although this was not stated) supplied from a breaker in the service equipment panel to the left, therefore the neutral should NOT be bonded to ground.

    Under emergency generator power, this panel would be "service equipment" and therefore the neutral SHOULD be bonded to ground.

    You can see the conundrum in the above to statements: the neutral SHOULD/IS NOT ALLOWED TO BE bonded to ground in that panel.

    When the main breaker is moved to the left, utility power is on; when that main breaker is moved to the right, generator power is on. The branch circuit breakers are supplied by EITHER (not both) utility power or emergency generator power.

    The neutral conductors may actually NOT BE multiple tapped as that terminal may be two separate terminals (I cannot tell from the photo), however, because you were on-site to see it, I will go with your call that the neutral is multiple tapped ... of course, though, that brings up the question of 'If the neutral is multiple tapped, and there is no other neutral terminal sized for that conductor, 'where' is the other neutral supposed to be terminated in that panel?

    The correct way to have installed that panel, although that panel does not appear to have been designed for this installation, would be to feed that panel with the utility power to the right breaker, emergency power to the left breakers (so far so good as the panel is designed for that) and then feeders feeding off to the panel on the left, which would no longer be the service equipment during utility power usage.

    Based on the above, that makes me wonder is this was only intended to be used for a 60 amp service equipment panel from the two sources and was never intended to feed another panel (and not be fed from another panel either).

    I am open to other replies which can clear up some of the questions I've raised about that emergency "panel".

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  4. #4
    James Duffin's Avatar
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    Default Re: Generator subpanel...??

    Quote Originally Posted by Jerry Peck View Post
    (Sigh.)

    If you guys would not insist on using the term "sub" in front of panel I suspect that you would realize that is a manual transfer switch/emergency power service equipment panel (especially James and I believe James says he is an electrician).

    The top right breaker is (apparently, although this was not stated) fed from the service equipment panel to the left. Therein lies a problem in that the service equipment to the left is, under normal utility operating conditions, the service equipment and therefore the grounds in this panel (for right now I will just call this a "panel" and not call this "manual transfer switch/emergency power service equipment panel" as that implies it is "service equipment", which it is under one operating condition, but not under the other operating condition).

    Under normal utility power, this panel would be (I suspect, although this was not stated) supplied from a breaker in the service equipment panel to the left, therefore the neutral should NOT be bonded to ground.

    Under emergency generator power, this panel would be "service equipment" and therefore the neutral SHOULD be bonded to ground.

    You can see the conundrum in the above to statements: the neutral SHOULD/IS NOT ALLOWED TO BE bonded to ground in that panel.

    When the main breaker is moved to the left, utility power is on; when that main breaker is moved to the right, generator power is on. The branch circuit breakers are supplied by EITHER (not both) utility power or emergency generator power.

    The neutral conductors may actually NOT BE multiple tapped as that terminal may be two separate terminals (I cannot tell from the photo), however, because you were on-site to see it, I will go with your call that the neutral is multiple tapped ... of course, though, that brings up the question of 'If the neutral is multiple tapped, and there is no other neutral terminal sized for that conductor, 'where' is the other neutral supposed to be terminated in that panel?

    The correct way to have installed that panel, although that panel does not appear to have been designed for this installation, would be to feed that panel with the utility power to the right breaker, emergency power to the left breakers (so far so good as the panel is designed for that) and then feeders feeding off to the panel on the left, which would no longer be the service equipment during utility power usage.

    Based on the above, that makes me wonder is this was only intended to be used for a 60 amp service equipment panel from the two sources and was never intended to feed another panel (and not be fed from another panel either).

    I am open to other replies which can clear up some of the questions I've raised about that emergency "panel".
    Like I said...a four pole transfer switch would solve the problem. Then the sub-panel could be wired like a service and a sub-panel...as needed. Just curious...how many transfer switches have you wired?


  5. #5
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    Default Re: Generator subpanel...??

    We have a built in generator system with an automated transfer switch that is a separate panel from the two circuit breaker panels. Without such a system I'd suggest checking with the local electric utility and see what they allow for. If there's a potential to feed power back into their lines and jeopardize their employees they could come up with a real simple solution - disconnect the home from their system.

    Eric Barker, ACI
    Lake Barrington, IL

  6. #6
    James Duffin's Avatar
    James Duffin Guest

    Default Re: Generator subpanel...??

    Here is a typical wiring diagram:

    Attached Files Attached Files

  7. #7
    Steve Boyer's Avatar
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    Default Re: Generator subpanel...??

    I thank you for all the replies, but I do want to note that this indeed was designed for just this type of installation, which kind of threw me. I checked my notes and it was a Murray GT6604NR and it stated on the inside of the cover "Suitable for use with optional standby systems in accordance with article 702 of the National Electric Code".

    The top breakers were two 60 amp 240's ganged together so when you switched one on, you switched the other off. It was fed from the main panel through a 50 amp breaker.

    I have a feeling that since the box could be used as a service panel also, that there was another ground bar that was to be installed if it was not being used as a main panel. There were neutrals and co-mingled so it was easy to recommend an electrician look at it...but I would like to understand this type of installation in case I see it again. Actually, I would also like to add something like this to my house to run a few essential circuits when lengthy electrical outages happen. I have an 8000w generator that would run a few circuits just fine. My generator has circuit breakers on it...I wonder if the grounds have to have a path back to the generator when it is running?

    Anyway, this is a standby generator panel...I just don't think this one was installed correctly... Might give Murray a call and see if they still make these. If a legal and safe installation is possible, it would be nice in my basement...

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  8. #8
    Steve Boyer's Avatar
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    Default Re: Generator subpanel...??

    After composing a question email to Murray tech support, I had an epiphany. (never use that word much). I feel this panel indeed needs a separate ground bar and all service grounds should be isolated to it. There should be a 4th wire/ground coming from the main panel bonded to the ground bar in the generator panel. The fourth wire/ground coming from the generator should be bonded to BOTH the neutral bar in the generator panel and the ground bar in the generator panel.

    I do not know if Murray will answer a question from a Home Inspector, but is there any reason this would not make the panel right?


  9. #9
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    Default Re: Generator subpanel...??

    Is that a male or female cord cap on that cable that feeds the panel from the generator?
    What size is the cord cap ( as in amperage)


  10. #10
    Steve Boyer's Avatar
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    Default Re: Generator subpanel...??

    I believe it was 30 amps which was the max amps the gen could output. It is a male and female connection. I did ask why there was a connection here since it plugged into the generator when needed, and the own said he wanted to have one more way of disconnecting the generator. Didn't discuss it further, but it seems totally redundant and a waste of money.

    Also, for what it is worth, I got a call back from Siemens on my query. (They own Murray). The tech said that this should have a separate ground bar and the ground should all be separated from the neutrals...including the generator. There should be a 4 wire from the main...with it connected to the ground bar... and it would be all set.

    He said "This should be treated like any other subpanel, and subpanels should have all grounds isolated". This is straight from Siemens support. I asked if the generator ground should be bonded to both the neutral and ground and he said that is not how it was designed, and that would defeat the ground bar isolation.

    Made sense to me.


  11. #11
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    Default Re: Generator subpanel...??

    It is NOT another "service" panel, it is a panel for an SDS. Separately Derrived System.

    Other might be transformer, solar, wind, etc.


  12. #12
    Roger Frazee's Avatar
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    Default Re: Generator subpanel...??

    If you notice the panel comes equipped with main lugs and a main bonding strap/jumper and pre-drilled holes on the left side of the panel for a grounding bar. It is suitable for both service equipment and a standby generator system. In a standby situation it is a manual transfer switch and it would not be separately derived by the fact you would have no way to switch the neutral and as such you would be solidly connected to the utility neutral. In standby/emergency configuration unless you can switch the neutral as with a 4 pole transfer switch the system will never qualify for separately derived.
    Having said that the panel can be used on a separately derived system via the main lugs with a 3 wire supply and use of the main bonding jumper. However, in this configuration it would not be used with emergency/standby power and the interlocked 60 amp breakers would be removed and branch breakers installed or it could be used as a panel load side of the service equipment. It's sort of a universal panel IMO.
    As it is pictured it is incorrectly wired. It needs the grounding bar installed in the left side of the panel with a 4 wire feeder from the service equipment when operating under utility. The 4 wire feeder from the generator is correct only you would of course terminate the egc to the installed grounding bar.
    Personally I would have purchased a power inlet for the generator connection but there is'nt a real problem with the present cord and plug setup IMO.

    I'm not quite following the inability to isolate neutral and ground with 4 wire feeders. You would only be required under standby configuration (for this type transfer switch) to isolate at the transfer switch as you would be bonded at the service equipment. The below link is essentially what you would have with the pictured panel in this thread. Only the panel and transfer switch are in the same enclosure.

    Google Image Result for http://www.imsasafety.org/journal/ma03/Fig%202.jpg

    As the panel is presently wired you have parallel paths for neutral current over the generator egc and neutral assuming a bond between the two exists at the generator. which is generally the case for portables .. and this being a 30 amp generator I would just about bet that the generator has bonded neutral and ground.

    Last edited by Roger Frazee; 04-23-2011 at 11:01 AM.

  13. #13
    Steve Boyer's Avatar
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    Default Re: Generator subpanel...??

    Roger,
    Thank you. That makes the most sense of all. I called my client with the information and the sellers already had an electrician in. He too thought the separate ground was needed and installed one. I personally think this was a "brother in law" type of install and not an electrician, but sellers will be sellers. The generator is going with the house, so it is nice to know it was straightened out. Your assessment agrees with Siemens.


  14. #14
    James Duffin's Avatar
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    Default Re: Generator subpanel...??

    Good info Roger...I made me a copy of it.


  15. #15
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    Default Re: Generator subpanel...??

    Isolating grounds in the panel may not singularly "solve" the problem installation.

    "If the generator neutral is grounded then the generator can only be used with a transfer switch that transfers the neutral" (SDS). Not all generators are listed to be and include instructions to separate N and G (although some as easy as a change at the terminal block, not all are otherwise isolated, and not all may/can be isolated in the field and maintain their listing). Was/is that a 3 or 4 prong/blade cap/cord set?

    Lots of changes in the NEC since 2002.

    Last edited by H.G. Watson, Sr.; 04-24-2011 at 12:25 AM.

  16. #16
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    Default Re: Generator subpanel...??

    This is not a 'separately derived system' unless the grounded conductor/neutral is switched.
    Only the power from the Utility is considered 'Service'.
    Bonding of the grounded conductor/neutral can be made in the transfer panel or the main service panel. The transfer panel would have to be adjacent to the main service panel if the bonding is done in the main service panel. If it is made in the transfer panel, then a 4-wire feeder must be run to the original main service panel and the neutrals isolated therein.
    The transfer panel is to be service rated unless there is a service main ahead of it.
    The grounding electrode conductor(s) are to be terminated on the neutral buss where the main bonding jumper is installed.

    These are some of the code rules to keep in mind before evaluating a genset installation.


  17. #17
    Steve Boyer's Avatar
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    Default Re: Generator subpanel...??

    Cap cord set was 4 blade, 4 wire


  18. #18
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    Default Re: Generator subpanel...??

    Steve Boyer,

    Thank you for following up. Seems the only hurdle then is to confirm the Generator is listed to be and may be used isolated and confirm the wiring (diagram, instructions, etc.) and assure it is isolated throughout N from G so you don't have an opportunity to create a parallel path while in use and risk objectional current via the Generator installation. As I mentioned before, some Generators are manufactured & listed to only be used free standing or as an SDS and may not have N & G isolated throughout with just a terminal block to deal with, and some that may, require more than one adjustment/modification to be able to do so - safely.


  19. #19
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    Default Re: Generator subpanel...??

    don't forget about the requirement for a sign on the service equipment, giving location and type of stand-by power.


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