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  1. #1

    Default Tap for subpanel into main lug

    I should know this - but don't. I inspected a home with upgraded 200 amp service. Panel wiring nicely done. The electrician had both the service conductor from the panel AND the feed to a subpanel in the same (oversized) lug.
    Can this be done? thoughts appreciated.

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  2. #2
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    Default Re: Tap for subpanel into main lug

    Quote Originally Posted by Ernie Simpson View Post
    I should know this - but don't. I inspected a home with upgraded 200 amp service. Panel wiring nicely done. The electrician had both the service conductor from the panel AND the feed to a subpanel in the same (oversized) lug.
    Can this be done? thoughts appreciated.
    Probably not. Need to look at the data plate on the panel.

    From the NEC:
    110.14(A)
    Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.

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    Default Re: Tap for subpanel into main lug

    Also, that feed is now unfused. I believe an unfused feed is acceptable in specific instances (don't feel like looking it up right now). Even if it is acceptable, it would be better to have it connected to a circuit breaker.

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  4. #4

    Default Re: Tap for subpanel into main lug

    Thanks for feedback, Gunnar.
    The picture didn't show this but the main disconnect was on the exterior. The service to the subpanel would then have the same overcurrent protection as the main feed coming into the panel. (I realize that if the disconnect was not on the exterior then this would have a service lateral to the subpanel with no overcurrent protection - but that was not the case). It seems to me that the critical thing is: was this lug designed for two large service conductors? I told my client that worst case would be installing another 'main' breaker in the panel and running the service to the subpanel off of that.


  5. #5
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    Default Re: Tap for subpanel into main lug

    Most likely that lug was only for one conductor .

    All answers based on unamended National Electrical codes.

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    Default Re: Tap for subpanel into main lug

    Quote Originally Posted by Ernie Simpson View Post
    The picture didn't show this but the main disconnect was on the exterior. The service to the subpanel would then have the same overcurrent protection as the main feed coming into the panel.
    .
    .
    It seems to me that the critical thing is: was this lug designed for two large service conductors?
    As I understand your description:

    1) The service equipment panel is on the exterior (that is where you described the main service disconnect to be).

    2) The electrical panel in the photo (which you did not describe as a "subpanel", yet it is no different than the electrical panel which is elsewhere which you described as a "subpane" ... which is yet one more reason to drop the "subpanel" term and just call it an "electrical panel") needs to be rated to at least the rating of the service equipment disconnect, as does the feeder to that electrical panel, the feeder to the electrical panel which is some place else, and to the feeders to that other electrical panel.

    To me, 2) is the critical issue, but you did not (unless I missed it) state that the ratings of the two electrical panels and the two feeders are properly rated to that of the service equipment disconnect rating - I am curious as to if those are properly sized.

    Yes, whether those terminals are rated for one conductor or two is important, quite important, but I think the ratings are more "critical" than the ratings of those terminals ... but that could just be me.

    (I realize that if the disconnect was not on the exterior then this would have a service lateral to the subpanel with no overcurrent protection - but that was not the case).
    I'm not following your statement of where the service disconnect would be if not on the exterior and about calling some set of conductors "service lateral"???

    I told my client that worst case would be installing another 'main' breaker in the panel and running the service to the subpanel off of that.
    What I think ... but am not sure ... you are describing is this - 'remove the feeders coming off those terminals, installing a sub-feed breaker off the panel (if space is available), then connecting those feeders off that breaker ... if I got what you are saying correctly??

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Tap for subpanel into main lug

    It would appear that the wire to the second panel and the wire from the main breaker/ service disconnect are the same size. It would be very uncommon for the first panel to have a buss rated for a 200 amp branch breaker (not impossible). These type panels are usually limited to 125 AMP branch breakers, but, the panel label needs to be checked to find out for sure. If the buss is rated for a 200 AMP breaker, and they make one to fit, it would likely take 8 1 inch spaces in the panel - 4 vertical spaces on each side.

    Probably the best bet is a Polaris type connector that takes 3 wires - wire from service, wire to second panel, and a new jumper to the first panel. Next would be to see if there are acceptable 2 hole lugs to replace the ones on the first panel. Lugs would look better, connectors likely much easier to come up with.

    Without knowing the calculated load on the second panel reducing the available current (smaller breaker) wouldn't be a good idea.

    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

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    Default Re: Tap for subpanel into main lug

    You wouldn't necessarily be reducing the available current to the second panel ... the main breaker is limiting the current to both panels to the rating of the main disconnect.

    The only way to increase current to the second panel would be to turn all breakers in the first panel 'off'.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Tap for subpanel into main lug

    It is a waster of higher rated panels as wired - presuming Bill's 200 amp rating for the service disconnect is correct, the feeders would need to be 200 amp rated (to the first panel, and to the second panel), and the first panel would need to have 200 amp rated mains ... as would the second panel ... yet only 200 amps is available for both panels combined.

    Does not make much sense, but if all were rated for 200 amps (in the example) all would meet code.

    Reminds me of a mall we were wiring decades ago when I worked for a large electrical contractor - each smaller store in each grouping of eight smaller stores had 200 amp panels, each group was feed by 400 amp mains ... might as well have put 60 amp panels with 50 amp mains in each small store ... kind of like feeding a 2-inch fire hose with one 1/2-inch garden hose ... not going to get more out the other end than can get in at the supply end.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Tap for subpanel into main lug

    Jerry,

    I don't think you took what I wrote quite right as I inferred that a smaller breaker (than a 200 AMP branch breaker) to power the second panel from the first one wouldn't be a good idea. (99.9% of the load could be on the second panel)

    One solution to solving the "multi tap" issue with the lugs would be to use a smaller breaker to power the second panel from the first one as it would in all likelihood be much easier to obtain. Just put it out there that it wouldn't be a good idea without other information.

    In any event, it looks like any solution except different lugs would require splicing and that makes the Polaris type connector the preferred choice to me as it doesn't pass the second panel load through the first one unnecessarily.

    Last edited by Bill Kriegh; 06-10-2017 at 10:53 AM.
    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

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    Default Re: Tap for subpanel into main lug

    Bill,

    I understood what you were saying, which is why I pointed out that having (in your example) two 200 amp panels fed through one 200 amp main is useless as the only way to get 200 amps through one is to completely turn all the breakers in the other panel 'off'.

    The Polaris type connectors will solve the multiple tapped condition, but will not address any other 'uselessness' of the installation (uselessness in being able to use the full rating of each panel).

    We don't have enough information to address for 'practicality' as we have no information on which panel is loaded to what amount - I am simply stating whatever the service disconnect is rated for (let's again use 200 amps), the feeders and both panels would need to be rated for at least that much ... which is a waste of higher panel ratings and conductor sizes.

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

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    Default Re: Tap for subpanel into main lug

    Well Jerry, nobody said we were looking for a rational installation here, just a legal one.

    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

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    Default Re: Tap for subpanel into main lug

    Quote Originally Posted by Bill Kriegh View Post
    Well Jerry, nobody said we were looking for a rational installation here, just a legal one.
    Bill,

    While that is correct - a home inspector reporting two 200 amp panels can leave the client with the impression that they have a 400 amp service ... unless the home inspector points out and explains why it is really only a 200 amp service - which is why I pointed that out.

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

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    Default Re: Tap for subpanel into main lug

    Bill;

    I live in Colorado also, and the way the photos are is just wrong in my eyes. Mainly safety. 1. Fire dept. shows up for a fire so they cut the main electrical service too the house??? To me which one. 2. I do know through experience that it is not correct by ANY regional building inspector to what appears to be and this is just me saying this, "A DOUBLE TAP" on the main electrical conductors. Plus I know that if COS regional dept. does not have their green tag affixed to the inside of the panel stating it is a correct install then in my eyes it is questionable and I will write it up as such with a recommendation and further evaluation and just move on. I enjoy your post, good conversation.




    Quote Originally Posted by Jerry Peck View Post
    Bill,

    While that is correct - a home inspector reporting two 200 amp panels can leave the client with the impression that they have a 400 amp service ... unless the home inspector points out and explains why it is really only a 200 amp service - which is why I pointed that out.



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    Default Re: Tap for subpanel into main lug

    Quote Originally Posted by Ernie Simpson View Post
    I should know this - but don't. I inspected a home with upgraded 200 amp service. Panel wiring nicely done. The electrician had both the service conductor from the panel AND the feed to a subpanel in the same (oversized) lug.
    Can this be done? thoughts appreciated.
    The short answer is no. The sub-panel should be fed through a breaker from the main panel (unless it is being fed from a feed through panel where the MOCP is for both panels. In which case it is not a sub-panel.) A sub-panel should also be 4 wire with the bonding to the can done on the ground side.


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