I would like to wire up the inverter on my boat to be very simple to
switch on and connect into the boats mains wiring. Ideally I want just
one switch. I am happy for this to be a big battery switch. I want the
plugs and other mains appliances (microwave, some lights etc) to just
work when I flick the switch. This is further complicated by the need to
not run other things - the battery charger is the only one that comes to
mind - from the inverter.

I am thinking about using a relay which will automatically disconnect
the inverter from the internal cct breaker and fuse panel if shore power
is connected. The same relay can also connect up the shore power only
circuits.

To do this seems simple... I use a 3 or 4 pole DT relay which is
energised by the shore power feed and will connect the feed to the fuse
panel input. When shore power is removed the relay will switch the
inverter output to the fuse panel input and disconnect the battery charger.

Does anyone see a problem with this? The only worry I had was that there
could be an issue with voltage spikes when the mains is unplugged and
some motor or coil gets connected to the inverter as its field collapses
(which may or may not be actually on). Presumably the inverter is
protected against such things cause by the DC power vanishing but having
the relay there means that the voltage switched on to the inverter when
the contacts eventually close could be quite high. Do inverters normally
have protection against such transients?

Alternatively, a 12VDC energised relay could be used that is on the same
switch as the inverter power. It would then disconnect the shore power
if the inverter is on. This has a couple of draw backs. 1) I need to run
the relay whenever the inverter is to be used (ok I know it is
insignificant but... well - you know!..) 2) I don't get an option for
automatic fail over if shore power fails. Which may be a good or bad
thing but at least it is an option. 3) the big spike could end up on the
shore power plug but I don't think will be any worse than when you
unplug the shore power by pulling the plug out.

Thanks in advance,

Steve