Sean Welsh (Sean) (64.81.73.194)
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Votes: 0 | | Posted on Tuesday, January 07, 2003 - 2:12 pm: | |
Folks, I need some help from the more experienced engineering types on this board.
I am working through my wiring diagrams, and have come across a challenging problem with the installation of my Xantrex/Trace SW4024 inverter/charger. Here's the (lengthy) description:
I originally (before settling on the Trace) had planned to have a standard 3-pole (two hots, one neutral) AC Automatic Transfer Switch (ATS) to switch between shore power (which might be as small as 15 amps/110 volts) and generator (which can deliver 60 amps/240 volts). The inverter/charger would have been one of several loads switched between these sources with the ATS. This design, however, does not take advantage of some of the automatic features of the high-end Trace unit, which is already equipped for dual inputs (Shore/Grid and Generator). So I am now reworking my diagrams to connect the grid input of the Trace to the shore cord and the generator input of the Trace to, naturally, the generator.
The Trace does not have an internal ground-to-neutral bonding relay, and the installation instructions clearly spell this out and even provide diagrams for how to install such a relay externally to effect proper ground-to-neutral bonding when stand-alone, and disconnect same when grid-connected. However, these diagrams and instructions only show one AC input -- dual AC sources are not covered.
The problem lies in the fact that the Trace's internal transfer switches only switch hots. The neutrals are internally tied together (both AC input neutrals and the AC output neutral are internally bonded). With only a shore cord to contend with, this is not a problem -- the ground bonding scheme suggested in the manual will work fine. However, the generator has the ground and neutral internally bonded as well. This is true whether the genny is running or not. (AFAIK, all generators are like this.) So as long as the generator neutral is wired to the neutral terminal of the Trace, plugging (the other AC neutral terminal) in to shore power will result in a ground loop through the generator.
I've come up with several possible solutions to this, but none of them is pretty.
That being said, I know the SW4024 is a popular inverter, and I assume most folks have both generators and shore cords, so someone has had to solve this before me. Thus my question: if this is your setup, what did you do to resolve this problem?
Whew. Sorry for the long-windedness, and looking forward to your answers!
-Sean |