Just to clarify this issue:

The only place the neutral could be carrying twice the design current
would be in the shore power cable. Since that cable surely would not be
used to connect the onboard inverter to the boat's AC system, we can
forget about it.

From the distribution box, each of the two 120 volt branches would
already have properly sized neutrals. How could they not?

There should be no question that the single-phase inverter's neutral is
the same size as its hot wire.

So there is simply no part of the proposed system in which a neutral
wire will be carrying more than its intended current.

The only other way an undersized neutral could be an issue is if the OP
wanted to convert his shore power cable to a 120 volt cable by simply
switching the plug and paralleling the two hot conductors. Since this is
probably the farthest thing from his proposed plan, there is no need for
concern.

Hope this helps.

Chuck

Jasen Betts wrote:
["Followup-To:" header set to rec.boats.electronics.]
On 2005-11-14, 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?


make sure your neutral wire is thick eough (or fuse your supply's
live output apropriate to its thickness) as the neutral wire will be
acrrying upto twice as much current as it would have with the two
180 degree phases.