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Thread: Complicated system bonding

  1. #1
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    Complicated system bonding

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    I've got a customer with what I feel is a complicated service in which the grounding and bonding has been modified in the past and doesn't meet code anymore. I'll do my best to explain the scenario but please take a look at the diagrams as they might help to clarify what I'm saying. Any input would be greatly appreciated.

    So it's a residential 400A service with all of the service equipment in the garage and feeders to a separate main house. There is a diesel generator inside the garage as well. There is a CT enclosure with two sets of hots coming out of it.

    As best I can tell the original setup was this:
    From the CT enclosure one set of conductors fed a 200A fused disconnect with a main bonding jumper between the neutral, EG and GEC. Then that fed out to a 200A panel in the main house.
    The second set of conductors fed a 200 breaker panel with a main bonding jumper between the neutral, EG and GEC. This panel fed all of the circuits in the garage as well as a 90A feeder to the house.

    Then it looks like they later added the generator and that's where I feel the grounding and bonding got messed up. So currently the setup is this (also see attached/linked image):
    One set of hots leaves the CT enclosure and runs into the 200A fused disconnect. Then from there it feeds through a conduit over to the transfer switch and the returning conductors run through the same conduit back to the fused disconnect where they are spliced and head off to the house. The system bonding jumper is still in the fused disconnect enclosure where the neutrals, EG and GEC are all connected. The neutral in the transfer switch is floating.
    The second set of hots runs into the enclosure for the 200A garage panel where it’s spliced and runs UNFUSED over to the transfer switch. Then returning from the transfer switch back through the same conduit to feed the 200A main breaker in the garage panel. Again the neutral is floating inside the transfer switch. And all of the neutrals, EG and GEC are all bonded together in the 200A panel.

    So if you followed that, one set of conductors uses the the transfer switch as the service disconnect, but the system bonding is downstream in the 200A panel. The other set of conductors has the system bonding in the same enclosure as the first disconnect but it then runs in and out of the same transfer switch used as the service disconnect for the other set of conductors.

    So my plan to clean this up and make it right is to use the transfer switch as the first service disconnect (it is service rated), and relocate all of the bonding between the GEC, EG and neutral to be inside the transfer switch.

    What do you all think so far? Sound like the best option?

    But wait there’s more!
    I started questioning my decision to go this route because 230.7 stipulates that I can’t have service conductors and non-service conductors in the same raceway. And as I understand it, the conductors are considered service conductors up to the first disconnect (am I wrong?). Which means I would need to totally redo all of the conduit. UGH!

    So now that I’ve typed all this out and drew up the diagrams, I’m wondering if the right decision is to install a 2nd 200A service disconnect between the CT enclosure and the 200A panel. That way the only real change I need to make is to relocate the system bond from the 200A panel to the new 200A service disconnect. In the end that would make (2) 200A Service disconnects with all the system bonding inside those 2 enclosures, everything else would be downstream with neutrals separated.

    Thoughts? Thanks in advance for any input

    Rob

  2. #2
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    Be aware that it is also a code violation to have two separate feeders with the same system voltage to one building (with some limited exceptions, including IMHO if one feeder is from service and the other is from generator).

  3. #3
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    If it were me, I think I'd do a 400 amp main disconnect for the service and bond at that point and then route my feeders accordingly. It may take quite a bit of changing to make it happen, but in my opinion is the right thing to do.

    Sent from my SM-G935V using Tapatalk

  4. #4
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    Somewhat surprised the switch is service rated with no OCP so be it.
    I don't see it cut and dry since yoru OCP is "adjacent" to the transfer switch does that make the panels part of the service equipment so do they need to be bonded to the neutral ?
    Anything we say might be interpreted differently by your AHJ so I'd depend on him.
    As an opinion, I would isolate the conductors from the CT to the TS in their own conduit(s) and do my bonding/GEC connections from my TS.
    Golddiggers comments on 225.30 was the first thought I had on seeing your diagram but your AHJ may feel one on the "special conditions" apply.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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