Join Date: Aug 2006
Location: Arlington, VA
Thanked 11 Times in 9 Posts
Rep Power: 10
IMHO, it's not a good idea to wire an appliance which can draw up to 28 amps, together with other distribution circuits on the same 30-amp main switch panel.
1. The typical 30A connectors...male and female...found in use today are overrated. The load they can carry safely is often significantly reduced by poor contacts, surface corrosion, and other environmental factors. I would never trust a 30A connection to safely carry a continuous load of 30A. Much better to de-rate them to 20-25A. I just replaced the main 30A receptacle and dock cord on a clients boat today; it showed serious arcing and burning due to overload for the conditions (poor contacts, surface corrosion, slight overload, old wiring). It could have caused a serious meltdown or fire; we've seen lots of them at our marina, as I'm sure other long-time boaters have.
2. The setup in the diagram above is a disaster waiting to happen, especially for the unwary, tired, or forgetful sailor. Yes, the 30A breakers on the hot and neutral should trip when faced with a load much more than 30A, but only after some time; moreover, they could trip at the wrong time and cause a serious problem. For example, the tired weekend sailor returns to his slip on Sunday nite, plugs in, and sets out for home. The depleted batteries are hungry, the charger sucks a lot of amperage and, after a bit, the hot water heater kicks in asking for another 15-20A. Pop...the main breakers go, and the charger goes off along with the hot water heater. Result: no battery charging, no hot water (or other 110V appliance connected to the mains).
What to do?
Install a 2nd 30A circuit, or upgrade the AC system to a 50A circuit. Or, install a second, smaller battery charger which could happily co-exist on a single 30A circuit with other house loads.