We have a mini 1200watt heater from west marine.  We have used it for a few years mostly on the starboard circuit.  We put it on the port circuit this past weekend and it caused a fire on the white wire going to the block on the starboard wall behind the breaker panel.  The end of the wire that was on the block burnt clear through. This line came from the shore power breaker and went directly to the wall panel.  The wire was a 12awg but the main breaker is 30 amp.  The breaker does have two connections…so I was wondering if it breaks down the amps into two 15 amp lines?  If not then the wiring is undersized!  30 amp should be on 10awg.

I replaced the burnt wire with a 10awg and tightened all of the other connections as well.  The breaker never tripped… The only two