Went to the boat to install LED bulbs only to find that the shore power Buss A breaker on the main panel was off and had been so for several days. Wondered why. After checking the connections I turned the power back on only to have it shut off again and this time the reverse polarity light came on; very unusual.

There was much resistance when I attempted to remove the shore power cord from the boat receptacle. After much effort it came out and noticed that my almost new cord was burned on the neutral pin and socket; bad enough to melt the cord material. Something had hit the power source, either a power spike or bad cord.

After cleaning the neutral pin, the spare cord worked fine for this past week. My plan was to replace the Buss A boat plug with new as it has been on the boat since built in 1991. In the process I found out why the two Line circuit breakers were bypassed. For some reason the PO had sheared off the head of machine screw that secured one of the wires to the breaker (it looked as though they had tried to force a different machine screw thread onto the terminal). Rather than repair it he/she terminated both wires on the same post on both breakers thus bypassing the breaker safety function.

After fours hours of work both Line 1 and Line 2 breakers work as originally designed, Buss A shore power cord has a new receptacle plug and I learned some new things about the boats electrical system.

Buss A feeds 30 amps of power to the entire boat including the battery charger. Buss B feeds 30 amps of power only to the two reverse cycle air conditioning systems. The two running along with the sea water pump requires about 25 amps of power. With Buss B feeding power to the heat pumps that leaves Buss A with plenty of power to operate the rest of the boat systems. Now it all makes sense.

Normally, with just Shore Power A cord I select parallel Parallel Buss A/B on the far right side of the panel. That way I can operate at least one heat pump and any other appliance up to 30 amps. At some point if I ever want to connect Buss B cord to run the heat pumps in addition to Buss A cord to run everything else, the panel lets you select Air Cond/Power B, which supplies 60 amps by running both Busses as the same time. See link below.

http://1.bp.blogspot.com/-VsEt0qLk2A...er+Dee+049.JPG