Quote:
Originally Posted by ViribusUnitis  I was seeing a marine air 16000 BTU unit. That's 11 amps when it's running, and maybe 35 or 40 amps on start up. The mannufactor calls for a 45 amp breaker. Then you figure a 1500 watt water heater, that's 13 amps, give or take. Just between those two peices, your looking at 24 amps. And thats when everything is running nice and stable. If you've got the water heater heating up, and then the a/c kicks in, I would expect it to go way over the 30 amp rating of a cord. |
But that surge is only short term - it usually won't trip the 30A shorepower breaker.
FYI - Per the MarineAir spec sheet on the Cabin Mate series (document L-2314.pdf at Dometic's website), the recommended maximum sized breaker for either the 16k or the 12k unit is 40A @ 115V; minimum breaker size I've already stated. You're right - you have to be careful and manage your usage appropriately - just as I said.
Does one really need a 1500W water heater? Isotherm's water heaters are 750W - based on their thinking that when on shorepower, you have lots of time for water to come up to temperature. They include an inlet for cooling water from your engine to power your water heater while under way - it's probably the equivalent of a 1500 or 1750W element. I'm in the process of ordering such a unit to replace our old 1500W 19-gallon water heater - way too large for two people on a 51-foot sailboat.
That being said - any boat is a compromise. There's limited space (and usually budget) for all the comforts of a home on land. And things tend to be more expensive because they have to stand up to the marine environment, and there's extra safety considerations because of the higher probability of electrical faults due to moisture, vibration, and movement - much more so than a home on land. Things like stranded wire versus solid wire (handles vibration much better), oil/water resistant insulation for wiring, etc.
If you do end up purchasing a boat with only a single 30A inlet, you could always add a second - but that would entail some re-wiring, and you'd inevitably find that the initial install (even if factory installed) is probably not up to current ABYC recommendations. Or you could replace it with a single 50A inlet...
And in case there's still some confusion - yes, with two 30A inlets you do need two cords hooked up to two shorepower circuits. Increasingly, though, it seems most marinas have shorepower pedestals with a single 30A and a single 50A - so you could run a single 50A cable to a 50A-to-2x30A adapter - that's what we normally do...