Portable Generator Question: Separately and non-separately derived system
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Portable Generator Question: Separately and non-separately derived system


Portable Generator Question: Separately and non-separately derived system
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Thread: Portable Generator Question: Separately and non-separately derived system

  1. #1
    Join Date
    Jun 2015
    Middletown, CT

    Default Portable Generator Question: Separately and non-separately derived system

    I have a portable generator that I want to use a emergency power in the event of an outage. The main panel has has a manual generator interlock which allows either the main breaker or the generator breaker to be on but not both at the same time. It is not a transfer switch and the neutral doesn't get switched so my generator needs to be set up as a non-separately derived power source. This requires that the neutral bonding jumper in the generator be removed. If I do this the generator must be plugged into the main panel wiring via the generator inlet box, in order to have a neutral and ground connection prior to starting it and the generator can no longer be used as a stand alone power source. Also it it my understanding that labels need added stating that the generator is configured for this purpose. Is this correct?

    Also would there be any code violation or safety concern if I replace the jumper with a 30A switch that would be equipped with a lock plate and proper labeling that would prevent the switch from inadvertently being flipped to the wrong position. That way if the lock plate was reversed and the switch was set to ON the generator could be used as a standalone unit if the need arose. If that idea doesn't fly how about the addition of a terminal strip and some longer leads that could be located in a more accessible location.
    Last edited by Greg_E; 08-25-2015 at 11:20 AM.

  2. #2
    Join Date
    Feb 2012
    Kent, WA


    Depending on how you're using the generator (when portable) and whose rules you're under, I'm not so sure its an issue to have an unbonded standalone generator. Older generators are most likely not even labeled as to whether they are bonded or not (mine isn't). The OSHA rules are more stringent than the NEC, but even the NEC may not apply. If you're a contractor using it on a job site, then you'll have the worst rules (GFCI protection, bonded).

    Bonding a small generator isn't typically required (not connecting the neutral to earth removes the earth as a conduction path so it is somewhat safer). Large generators (15KW and larger) can couple voltage to the earth, so you'd have a possible shock path but it isn't a very good one. Static electricity can get dissipated through the metal frame if that frame sits on the dirt (the spinning rotor builds up static voltages). You only need a 1 Megohm path to dissipate static electricity, so you don't need a rod and wire.

    To me, the easiest solution, if you want to provide for bonding the generator when stand alone, would be to build a "shorting plug". Take a plug (ideally a 30A one if your generator has 30A receptacles), and connect a #10 wire between the neutral and ground. Insert this plug into the generator when using it stand alone and remove it when powering the house. This will only work if the receptacle you use does NOT have GFCI protection.

    If the generator has GFCI protection on all outlets, then you'll need to use your switch approach. Messing with this can void the listing, but again that may not matter depending on how it is being used, whose rules you are under, and how liability conscious you are. Is you generator even easy to unbond?

    Your interlock on the panel is a "transfer switch". I believe those are listed in most cases as transfer equipment. Where they are pushing us now, however, is to have transfer equipment that switches the neutral as that solves all the problems. More and more of those are available so the price is getting cheaper. But I do dislike all this additional regulation. I bought my unbonded generator 10 years ago and no one has been shocked from it yet...
    Kent, WA

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