In article ,
Peter Bennett wrote:

On Mon, 14 Nov 2005 10:14:18 -0500, Hoo
wrote:

My boat has two 120 volt circuits with a common neutral wire similar
to most homes. Normally they are supplied with 220 volts from either
a generator or shore power (120-0-120). There are no 220 volt
appliances or circuits out of the breaker panel.

I would like to be able to feed both 120 volt legs with a single 120
volt inverter through a rotary selector switch (both legs in phase,
instead of 180 degrees out of phase). There would be no possibility
of backfeed or cross connection with shore/generator power.

Does anyone know of any issues with doing that?

My only concern would be the size of the neutral wire.

When fed 120-0-120, the neutral current can never be more than the
current in either hot wire (it will actually be the difference between
the two hot wires), but if the two hot wires are in phase, the current
in the neutral will be the sum of the two hot currents.

If your inverter is 2000 watts or less, and the wiring is #12, you
will be OK, as the inverter will limit the total current to about 20
amps, and #12 wire is rated for that. If you have a larger inverter,
you may have to use larger wire.

The neutral question that Peter is concerned about would be dealt with,
IF you drive your 120-0-120 panel with wire that would support the total
current of all the loads at one time. I use this exact system for
feeding the panel in my cabin from my Trace 4024. As the cabin was
originally designed and fed as a 240/120Vac Single Phase, when I moved
in and introduced the Trace inverter, rather than replace the panel,
I choose to bring both legs together at the Transfer Switch that feeds
the cabin. In Winter Mode, It is driven by 120Vac directly from the
output of the 4024. In Summer Mode, it is feed by 208/120Vac, Two out of
Three Phase, from the 2.5 Megawatt Powerhouse Distribution System.
The feedwires to the cabin from the Winter Powerhouse are "2", so
that there is plenty of copper for the maximum load of te cabin, and I
have NO 240 loads on the cabin subpanel.


Bruce in alaska
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add a 2 before @