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Thread: Two switchboards

  1. #21
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    Quote Originally Posted by Wire-Smith View Post
    two neutral to ground bonds on one electrical system(the same transformer)at two separated areas connected by conductive paths, i think this is your real problem.
    Dont follow. Neutral to bond are at service disconnects and 250.50 all grounding electrodes need to be bonded together in building. If GEC are installed per nec 2014 article 250.64(f)(3) with busbar in electric room outside of service equipment would that create objectionable current?
    Last edited by hhsting; 01-25-19 at 09:27 PM.

  2. #22
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    Quote Originally Posted by hhsting View Post
    Dont follow. Neutral to bond are at service disconnects and 250.50 all grounding electrodes need to be bonded together in building. If GEC are installed per nec 2014 article 250.64(f)(3) with busbar in electric room outside of service equipment would that create objectionable current?
    you have one transformer feeding two panelboards and both have a neutral to ground bond correct?

    if so, everything grounded and bonded to both of those panels is effectively a parallel neutral and will carry part of the neutral current from either of the panelboards. its not a big deal if the panels are side by side, but in two separate areas, i see potential problems(sparking ground connections, shock hazards, etc.) and would red tag it if i was the ahj and would not do it if i was the contractor.

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    Quote Originally Posted by Wire-Smith View Post
    you have one transformer feeding two panelboards and both have a neutral to ground bond correct?

    if so, everything grounded and bonded to both of those panels is effectively a parallel neutral and will carry part of the neutral current from either of the panelboards. its not a big deal if the panels are side by side, but in two separate areas, i see potential problems(sparking ground connections, shock hazards, etc.) and would red tag it if i was the ahj and would not do it if i was the contractor.
    You mean attached sketch cause objectionable current? If yes then how are the two service swbd grounded and bonded?
    Last edited by hhsting; 01-25-19 at 09:48 PM.

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    you could eliminate the problem several ways

    1.) disconnect(s) before panelboards, if you use one then that's where your only main bond will be. if you use two, group the disconnects and those will be your only main bonds.

    2.)group panelboards beside eachother
    Last edited by Wire-Smith; 01-25-19 at 09:55 PM.

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    Quote Originally Posted by Wire-Smith View Post
    you could eliminate the problem several ways

    1.) disconnect(s) before panelboards, if you use one then that's where your only main bond will be. if you use two, group the disconnects and those will be your only main bonds.

    2.)group panelboards beside eachother
    How about attach sketch swbd#1 exterior wall fire pump room while swbd #2 inside fire pump room next to each other. Swbd #2 is for fire pump.

    Sent from my SM-G935U using Tapatalk

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    Quote Originally Posted by hhsting View Post
    Dont follow. Neutral to bond are at service disconnects and 250.50 all grounding electrodes need to be bonded together in building. If GEC are installed per nec 2014 article 250.64(f)(3) with busbar in electric room outside of service equipment would that create objectionable current?
    As long as the bonding jumpers to building steel, water system, CEE, or any other electrode used to make up the grounding electrode system, sized for the largest service i do not see a violation

    I do not think it matters if the Plate is in the area of service one or service two. By going to a boding plate with both services you have come as close as possible to a single point grounding electrode system as two service (laterals) will allow

    IMO at least,

  7. #27
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    Quote Originally Posted by hhsting View Post
    How about attach sketch swbd#1 exterior wall fire pump room while swbd #2 inside fire pump room next to each other. Swbd #2 is for fire pump.

    Sent from my SM-G935U using Tapatalk
    i would be comfortable with that, but would probably run a big bonding jumper from one panelboard to the other just for good measure and would personally still prefer one main disconnect(or two pretty much bolted together), although your illustration would be what i consider more inline with the more standard industry practice.

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    Quote Originally Posted by david View Post
    As long as the bonding jumpers to building steel, water system, CEE, or any other electrode used to make up the grounding electrode system, sized for the largest service i do not see a violation

    I do not think it matters if the Plate is in the area of service one or service two. By going to a boding plate with both services you have come as close as possible to a single point grounding electrode system as two service (laterals) will allow

    IMO at least,

    wait until one of these days you run across a building with a double bond and you lose one of the service neutrals, you'll see things like flex sparking against conduits, pipes. and it could also happen without losing a neutral but would likely not cause a problem unless you have decent neutral current, but then again it doesn't take much current to do a lot of damage under the right circumstances. i have heard of people feeling circulating ground current in the shower (albeit metal plumbing, but you get the hint).

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    Quote Originally Posted by Wire-Smith View Post
    i would be comfortable with that, but would probably run a big bonding jumper from one panelboard to the other just for good measure and would personally still prefer one main disconnect(or two pretty much bolted together), although your illustration would be what i consider more inline with the more standard industry practice.
    I do have swbd #1 enclosure bonded and swbd #2 enclosure bonded together. See attach sketch. Would it still require bonding jumper in between?

    Sent from my SM-G935U using Tapatalk

  10. #30
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    Quote Originally Posted by hhsting View Post
    I do have swbd #1 enclosure bonded and swbd #2 enclosure bonded together. See attach sketch. Would it still require bonding jumper in between?

    Sent from my SM-G935U using Tapatalk
    i didn't say it required it, just that i would do it.

    although i believe it is required in patient care areas if that happens to be the location. (if they serve patient care areas)(517.14)

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