RV Guy: Both ACs on same line?!?

[BarryD0706]

I haven't run both air conditioners very often but was doing it this afternoon. I looked at my Progressive Industries EMS unit and find that Line-1 is pulling 30 amps and Line-2 is pulling 2 amps! I was under the impression that the air conditioners would be on separate sides of the 50-amp service. Is this a mistake in my Sanibel? If not, what is the advantage of doing it this way?
(L-1: 113v. L-2: 120v)

[cfsoistman]

As long as the Microwave, Water Heater electric element and the receptacles are on the other side it should be ok. The GFIC circuit could be on the same side as the AC units also. Each AC is rated out at 20 amps so with both running the two would be protected out to 40 amps. Their running amps are probably close to 15 each. Our 50 amp service has 1 AC on each side and gfic receptacles and the regular receptacles on each side, then the microwave on one side and the water heater element on the other.

[RV Guy]

Hi, Barry - sorry for the delayed response but your inquiry forced me into more research than normal. Here's a very "NON CERTIFIED ELECTRICIAN" response to your question.

There are two lines on a 50 AMP Service as you mention. If you were to count up all the various circuits that go into a 50 AMP service you would have over 100 AMPS easily with several 20 AMP breakers and several 15 AMP breakers dispersed equally in the system. Obviously, we are all familiar with the typical power management requirements in an RV and this is the way they are all built (whether 50 AMP of 30 AMP) so this isn't a surprise.

Where it gets tricky is how to allocate all of the circuits given there are two "legs" to the 50 AMP. You might have both A/Cs on one leg, but you're also going to have a lot of other huge power users on the other leg. For instance, Microwaves and Water Heaters both use a lot of AMPs. To a large extent, we try to balance out the two "legs" with an educated guess on how our customers would prefer to use their RV and everyone has different needs, so that can be difficult to guess correctly.

If, because of the way you use your Sanibel, you wanted to have a certified electrician switch one of your A/C circuits to the other "leg" and move something (water heater maybe?) back in it's place, that is relatively simple to do.

Your question generated a lot of discussion at our place in trying to determine the preferred method of allocation but I'm not sure we came up with a sure-fire answer that every customer will like.

Hope this helps.

PTM

[BarryD0706]

RV Guy,
thanks for your thoughts and analysis on this. I certainly agree with your approach for trying to make sure that we aren't going to exceed the 50-amp ratings on either line in "normal" use of the RV, even briefly.

Probably the thing I would emphasize a bit more is the duty-cycle of the appliances. You mentioned that the microwave uses a lot of amps. Yes, but in most cases that is probably only for a minute or three out of a whole day. (I appreciate that it's a convection oven as well so some people could be using it for much longer times... but even 2 hours is relatively short compared to how long an AC will be running, and I would guess that less than half of your customers routinely use it as a convection oven.)

The water heater is somewhat similar in that, once the water gets hot, it's probably drawing current less than 25% of the time.

I think the AC units are probably the most sensitive of anything in the RV to having low voltage shorten their lives. Having low voltage for a short period of time (the minute the microwave is on) is going to have much less of a detrimental effect than having both ACs pulling the line voltage down for many long hours.

I understand that these tradeoffs are hard to make, and those who don't live in the southern heat will probably use their ACs about as much as I use the microwave.

As an aside, another thing I've noticed at the parks I've visited is that the line-1 voltage is always lower (by a few volts) than the line-2 voltage. My guess is that this is because manufacturers always start out with the big things on line 1 and then put the left-overs (washer/dryer) on line 2. Spread that out over a whole campground and you've got a pattern. (I doubt the electrician who wires the place does anything to try to balance that out; after all, "the black wire always goes on this terminal and the red wire always goes on the other terminal". Since 30-amp service is always black, white, and green, all of the 30-amp outlets probably go on the 50-amp "line 1" (black) as well.)

It might be a good idea to always reverse line-1 and line-2 in wiring up PrimeTime 50-amp units...until you take over the world, at which time you'd have to change to randomly switching between the two options in order to keep the world in balance.

Back to the original topic, I'm going to give some thought to what I think would be a better split of the existing circuits across the two lines in my Sanibel and will post that, along with my rationale, once I've thought it thru.

Thanks again.