Quote:
Originally Posted by ChuckS
The initial current surge is going to exceed 50 amp service sooner or later at some point with two units running and a third kicking in... the standard OEM RV power cable plug ends... let alone the overall size of the cable wiring would be marginal at best without a power management device...
might get away with it for a while without power management but the cord and plug ends are gonna be hot
|
First, EVERY trailer should have an EMS installed and IMHO, it should become a factory standard item, just like the water heater, microwave and furnace.
That said, I'm not sure I completely agree with the bolded statement. A 30 amp trailer provides 3600 watts of power on a single buss with a 20 amp breaker (2400 watts) for the air conditioner circuit.
A 50 amp RV provides two 50 amp busses, each capable of 50 amps (6000 watts) wiring two 20 amp breakers on one buss (4800 watts) and one 20 amp breaker (2400 watts) on the opposing buss would spread the power draw and wouldn't put the system in overload. Hypothetically, if all three A/C's started at the same time (2400x3) the maximum draw could be 7200 watts, still well below the 12,000 watt total available power.
Dometic's power requirements for generator sizing requires a 5500 watt generator to power 2 air conditioner units (500 watts below the 6000 watts available on one 50 amp leg).
Granted there "may be a start surge" that could "conceivably" cause a momentary overload, but the chances of that random start condition occurring is extremely infrequent. In the event it did occur, the circuit breakers on the double leg would open to protect the circuits from overload.
With an EMS in the RV, even that condition would be "protected by the EMS".
I would suggest that if an owner plans to regularly operate both A/C units that are wired to the same leg on the buss, then nothing else should be wired to that buss (that would also be regularly operated at the same time). If electric supplemental heat (in the furnace system) were to be considered, then wiring it to that side of the power distribution panel would be OK, since the A/C's and the furnace would not be operated at the same time...
I'd recommend, in that case, to use one leg of the power panel for HVAC and the other leg for "the rest of the trailer plus the "3rd A/C unit"...
As you said, with an EMS in the system, the trailer would be protected from the "low voltage" possibility if the circuit breakers did not open in the extremely rare situation where both A/C's on one leg might call for a compressor start at the same instant...
The problem, as I see it, is a campground grid that suffers from frequent overload and subjects the trailer (any trailer) to low voltage... That, coupled with three A/C's in a 50 amp trailer, without an EMS, is a "sure way to have electrical problems"... Sooner rather than later.... The same situation would occur, even with a 30 amp trailer and one air conditioner, not because of inadequate wiring or trailer capacity, but because of the low voltage condition that results from inadequate campground grid.