Sean Welsh (Sean) (64.81.73.194)
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Votes: 0 | | Posted on Wednesday, January 08, 2003 - 1:30 am: | |
Perhaps I was not clear in my original posting, or maybe I stated the problem incorrectly.
Code (NFPA 1192 as well as NEC) *and* safe practice mandate that the neutral and ground be bonded in only one place, and that place should be as far upstream as possible. In a correctly wired park, the neutral and ground will be bonded upstream of the receptacle -- usually either at the subpanel where the circuit breaker for the receptacle is located, or maybe all the way back at the transformer from which the subpanel derives. (If you need an explanation of why violating this can be dangerous, see the discussion in the "NEC Handbook.")
So, if you have the neutral and the ground tied together anywhere in your coach, AND you plug your coach into shore power, you now have the neutral and ground bonded in two different locations.
My error is in referring to this as a ground-neutral loop, which some have confused with a ground loop. What it really is is multiple ground-neutral bonds. This creates the potential for live current to be traveling through your ground system, including possibly the vehicle chassis.
I'm not looking for advice on how to test grounding -- I have a great meter already, I'm an engineer, and I have designed hundreds of electrical distribution systems (mostly large fixed installations with tens of thousands of amp-hours of batteries, and 480-volt three phase AC). What I'm looking for is an engineering solution to the multiple bond problem -- I could do the engineering myself, selecting relays and/or transfer switches, etc. and stringing them together. But I figure someone on this board has had to do this already, and I don't want to reinvent the wheel.
For what it's worth: The Trace does NOT have an internally bonded ground and neutral -- the installer must bond them somewhere else (see pp. 26-28 of the manual). And, as I mentioned in my original post, I don't want to revert to my original plan of only using the one input and having the transfer be completely external, because that precludes me from using the more sophisticated load-support features of the Trace.
So my question remains: Who is using a Trace SW series box, both AC1 and AC2 inputs, and a hard-wired generator, and how did you solve this problem? Or am I really clearing new ground here?
-Sean |