When your combination inverter / charger fails you lose shore power. 

That's right.  The inverter fails and you loose shore power, not just inverter power.  Along with shore power, you may lose the ability to plug in a backup battery charger.  You are in one tight spot. 

I install the 120 volt lines to and from the inverter with insulated tab disconnects.  If the inverter fails, you or I can disconnect it from the power wires and hook the wires together to bypass the inverter.  This gets you back in business while you figure things out.  It also makes life easier for me when you call.  I can pop the inverter out quickly and later pop it back in quickly. I can also talk you through the process yourself.

I started doing this after I got a few emergency calls to come and clean up after a dead inverter.  I arrange the male and female 30 amp tab crimp connectors so that it's possible to both connect the inverter and bypass it.  You just keep the wire colors matched.  I put it together male-female so you cannot reverse AC polarity or short out shore power or plug the repaired inverter in backwards, even if you're color blind.

This assumes your inverter is wired in the manufacturer's recommended manner, where shore power loops through the inverter.  When the inverter senses stable power, an internal transfer relay pulls in and supplies your boat with 120 VAC from the shore.  If you lose shore power, the inverter automatically switches back to inverter power.

Now personally, I think it was an unfortunate idea for the first inverter / chargers to be set up with a transfer relay this way.  And I follow the manufacturer's recommended installation setup.  It DOES make sure the battery charger comes back on when you plug the boat in.  But my boat is not set up like this.  The bad consequences of the transfer relay idea include the following sequence of events:  Shore power cord gets inadvertently disconnected.  Inverter automatically starts sucking serious battery power.  Batteries run dead and the bilge pump quits.  You discover the situation (with a foot of water in the bilge) the day you come down to take guests out.  The batteries have been dead long enough to sulfate. . . .

The first picture shows the inverter connected normally. The second picture shows it bypassed.  The bottom picture (different model inverter) shows the wires nestled into the inverter's power connection compartment as well as the inverter removed on the left and the "to" and "from" wires connected together in the inverter's absence on the right.

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