third ac

[fuquatj]

We had the 3rd A/C installed in our 2017 3921FB shortly after we bought it. I'm no electrician, so can't provide wiring details, however I know that because our unit has the on demand water heating system, there was an unused breaker that would have powered the electric side of a traditional RV water heater. The 3rd A/C went on that breaker. All 3 A/C's will run at one time with the camper connected to 50 amps. I can't say positively that all 3 compressors will run at once, but I believe they will.

[Budman229]

Yes, you can if you are careful when you turn them on and watch what else is running. Our current RV has three. Turn them on one at a time and wait for the compressor to kick in before starting the next one. While they ALL are running, you won;t be able to run any other high amp appliances (elec. water heater/ Microwave etc.). With all 3 of ours running at the same time, they are drawing about 43 amps. After the RV has cooled down, ours seldom has all 3 running at the same time.

[AZ Traveler]

Originally Posted by Budman229

Yes, you can if you are careful when you turn them on and watch what else is running. Our current RV has three. Turn them on one at a time and wait for the compressor to kick in before starting the next one. While they ALL are running, you won;t be able to run any other high amp appliances (elec. water heater/ Microwave etc.). With all 3 of ours running at the same time, they are drawing about 43 amps. After the RV has cooled down, ours seldom has all 3 running at the same time.

You can run a lot more with the 57 remaining amps as long as systems are spread out on your circuit breakers. Remember a 50 amp hookup is really two 50 amp circuits.

[TAKPAK]

Originally Posted by AZ Traveler

You can run a lot more with the 57 remaining amps as long as systems are spread out on your circuit breakers. Remember a 50 amp hookup is really two 50 amp circuits.

Remaining 57 amps?? As mentioned, there is only 50 amps available, per leg. Two legs of 50 amps does NOT mean you have 100 amps, just 50 total. If you try to load one leg (either one) over the 50 amp rating, it will trip the breaker. A 15,000 BTU AC unit, AFTER starting draws around 14 amps (running current). Ideally, you could run all three AC units on one 50 amp leg, however it's the starting current on the compressor that kills that idea. I could go into the hertz/cycles thing, and the split bus, but that's getting too detailed. If you want to split hairs, the NEC electrical code book states that you should only load a rated circuit to 80 percent of it's rated capacity, which on 50 amps would equal a 40 amp load. I know, too much info, but I was a maintenance engineer/licensed electrician for 35 years and had to fix problems such as this.

[mtlakejim]

Originally Posted by TAKPAK

Remaining 57 amps?? As mentioned, there is only 50 amps available, per leg. Two legs of 50 amps does NOT mean you have 100 amps, just 50 total. If you try to load one leg (either one) over the 50 amp rating, it will trip the breaker. A 15,000 BTU AC unit, AFTER starting draws around 14 amps (running current). Ideally, you could run all three AC units on one 50 amp leg, however it's the starting current on the compressor that kills that idea. I could go into the hertz/cycles thing, and the split bus, but that's getting too detailed. If you want to split hairs, the NEC electrical code book states that you should only load a rated circuit to 80 percent of it's rated capacity, which on 50 amps would equal a 40 amp load. I know, too much info, but I was a maintenance engineer/licensed electrician for 35 years and had to fix problems such as this.

Now I'm confused. Let me try to look at it another way and tell me if I am correct.

On 50 amp RV plug you have two separate 50 amp each legs correct?

So if your wise you would have at least one of your three A/C units on the opposite leg from the other two?

If you had one A/C on one leg and the other two on the other leg could you then run all three? Assuming of course that the starting load was under 25 amps each.

If that is the case then why do they use the boxes to control A/C units such that not all three can run at once on 50 amp units? Seems like they would just wire the problem away? Why would anyone wire all three units on just one side (leg) of the 50 amp RV system?


Granted there are other things that pull power on an RV but depending on where you are located and how hot it is, the A/C units will take priority over everything else. I know they do for us in the SE New Mexico desert triple digit no shade climate!!!!

[TAKPAK]

Originally Posted by mtlakejim

Now I'm confused. Let me try to look at it another way and tell me if I am correct.

On 50 amp RV plug you have two separate 50 amp each legs correct?

You are absolutely correct on the above statement. Each leg has 50 amp capacity.

So if your wise you would have at least one of your three A/C units on the opposite leg from the other two?

IF the manufacturer did it correctly, then yes you should have two AC's on one leg and one on the other.

If you had one A/C on one leg and the other two on the other leg could you then run all three? Assuming of course that the starting load was under 25 amps each.

Assuming there were no other heavy loads, then yes you should be able to run all three, within the limits of what the pedestal power is capable of.

If that is the case then why do they use the boxes to control A/C units such that not all three can run at once on 50 amp units? Seems like they would just wire the problem away? Why would anyone wire all three units on just one side (leg) of the 50 amp RV system?

Back in some older models of RV's, there was a manual switch wired in that you had to change in order to run various heavy loads, without overloading the system. Now days it is done electronically. It's called "load shedding" and is done in a lot of commercial buildings. This would most likely be in very high end trailers and motorhomes. Keeps people from unintentionally overloading their system. Such as "gee, all AC's are running, I think I'll run the micro, or the dryer, or??"


Granted there are other things that pull power on an RV but depending on where you are located and how hot it is, the A/C units will take priority over everything else. I know they do for us in the SE New Mexico desert triple digit no shade climate!!!!

Yep. It all depends on what's most important to you. Keeping the AC running, or heating up that casserole, or drying your laundry. Hope this helps a bit. I could get a lot more technical (shall we talk 3 phase power) but I won't, not for this forum!!