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Old 05-07-2021, 06:05 PM   #1
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50 Amp Question

My Bighorn fifth wheel has two 15,000 BTU roof air units and 50 amp electrical service. I'll be staying in Tucson this summer, and I learned last summer that two AC units cannot handle temps over 100 degrees. To stay comfortable in June, July, and August I purchased a 10,000 BTU portable air conditioner on Amazon. My question: Can I plug the portable into one of the wall outlets in the coach, or should I run an extension cord out of the window to power the portable with the pedestal's 115V outlet? I'm concerned that I'll throw a circuit breaker in the coach by trying to operate the portable while the two roof ACs are running. That's a lot of amps I think, maybe too much for my 50 amp service. Thanks in advance for your thoughts.
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Old 05-07-2021, 06:11 PM   #2
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Originally Posted by edmck101 View Post
My Bighorn fifth wheel has two 15,000 BTU roof air units and 50 amp electrical service. I'll be staying in Tucson this summer, and I learned last summer that two AC units cannot handle temps over 100 degrees. To stay comfortable in June, July, and August I purchased a 10,000 BTU portable air conditioner on Amazon. My question: Can I plug the portable into one of the wall outlets in the coach, or should I run an extension cord out of the window to power the portable with the pedestal's 115V outlet? I'm concerned that I'll throw a circuit breaker in the coach by trying to operate the portable while the two roof ACs are running. That's a lot of amps I think, maybe too much for my 50 amp service. Thanks in advance for your thoughts.

If I remember correctly, the rooftop a/c's pull about 7 amps each, and are each on their own breaker in the panel. See what the portable pulls. You should be able to plug it in to another 20 amp recep (usually a kitchen plug) and be OK. Worst thing that can happen is a tripped breaker.
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Old 05-07-2021, 06:25 PM   #3
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Each 15k roof top A/C draw about 12-13 amps. Even with both of them running at the same time that is just under 25% of your total available power so I am not sure how that is "a lot of amps". You can turn on everything in your RV and probably not max out a a 50 amp connection. That is 12,000 watts.

Yes you can run off an internal circuit, however, how much amperage does the portable A/C use and what else is on the circuit? If you have another large item on the same circuit you would likely trip the breaker.
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Old 05-07-2021, 07:15 PM   #4
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Each 15k roof top A/C draw about 12-13 amps. Even with both of them running at the same time that is just under 25% of your total available power so I am not sure how that is "a lot of amps". You can turn on everything in your RV and probably not max out a a 50 amp connection. That is 12,000 watts.

Yes you can run off an internal circuit, however, how much amperage does the portable A/C use and what else is on the circuit? If you have another large item on the same circuit you would likely trip the breaker.
THIS^^^^^
And if CB trips it would be the 15A/20A Receptacle Individual CB not one of the Main 50A CBs
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Old 05-07-2021, 07:20 PM   #5
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On most electric posts there is a 20 amp receptacle. Just run a separate 20 amp cord and you will be fine.
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Old 05-07-2021, 07:59 PM   #6
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On most electric posts there is a 20 amp receptacle. Just run a separate 20 amp cord and you will be fine.
If you do this use a 12 gauge extension cord minimum. The shorter the better.
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Old 05-07-2021, 08:01 PM   #7
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With 50A RV...no need for external extension cord to run portable 10K A/C Unit
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Old 05-07-2021, 08:11 PM   #8
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It may be possible to trip one of the 50A main breakers, but not from the 3 a/c units alone. However, add in a the converter/charger, fridge, water heater (on electric?), maybe a washer/dryer, and a microwave and you could hit 50A if multiple of those happens to cycle on at the same time (thermostats seem to conspire to do that). I've seen one or the other leg of the 50A service to my coach hit 35-38 amps a number of times, so another a/c (even @ 7-9 amps) could push it close.
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Old 05-07-2021, 08:15 PM   #9
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Each 15k roof top A/C draw about 12-13 amps. Even with both of them running at the same time that is just under 25% of your total available power so I am not sure how that is "a lot of amps".....

Not sure of the math - 2x13A = 26A = just over 50% of a 50A service, right? Regardless, the real issue is starting 'surge' current which is way more than 13A per unit. Eventually you will have an event where 2 or more of the AC units will start simultaneously and most likely trip the breaker. Happened to us just the other day with 2 ACs and the AquaHot 110v heater on.



Throw in a likely tired circuit breaker on the RV site pedestal and you'll be doing the 'reset walk' more than you'd like if you run all 3 off of the same 50A service.
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Old 05-07-2021, 08:16 PM   #10
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My Class A has 3 rooftop A/Cs and I often run all 3 at once.
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Old 05-07-2021, 08:24 PM   #11
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Not sure of the math - 2x13A = 26A = just over 50% of a 50A service, right? Regardless, the real issue is starting 'surge' current which is way more than 13A per unit. Eventually you will have an event where 2 or more of the AC units will start simultaneously and most likely trip the breaker. Happened to us just the other day with 2 ACs and the AquaHot 110v heater on.



Throw in a likely tired circuit breaker on the RV site pedestal and you'll be doing the 'reset walk' more than you'd like if you run all 3 off of the same 50A service.
My math is correct. You understanding of a how a 50 amp circuit works is not correct.

15 amps = 1800 watts
30 amps = 3600 watts
50 amps L1 = 6000 watts, L2 =6000 watts for a total of 12,000 watts.

Even if both A/C were on the same leg it would still handle it. It would only be 50% of 1 leg. Typically there is 1 A/C per leg or ~25% of each leg.
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Old 05-07-2021, 08:40 PM   #12
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My math is correct. You understanding of a how a 50 amp circuit works is not correct.

15 amps = 1800 watts
30 amps = 3600 watts
50 amps L1 = 6000 watts, L2 =6000 watts for a total of 12,000 watts.

Even if both A/C were on the same leg it would still handle it. It would only be 50% of 1 leg. Typically there is 1 A/C per leg or ~25% of each leg.
You are correct
So RV 50 amp service is really 100 amps total
50 amps each line.
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Old 05-07-2021, 08:53 PM   #13
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You are correct
So RV 50 amp service is really 100 amps total
50 amps each line.
Yes so it is such an odd way of naming amps with RV's. If 30 amps is 30 amps why do we call 100 amps - 50 amps?

So 30 amps is 3,600 watts. 50 amps is 12,000 watts. Unnecessarily confusing!

https://koa.com/blog/30-vs-50-amp-rv-service/
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Old 05-07-2021, 08:57 PM   #14
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Yes so it is such an odd way of naming amps with RV's. If 30 amps is 30 amps why do we call 100 amps - 50 amps?

So 30 amps is 3,600 watts. 50 amps is 12,000 watts. Unnecessarily confusing!

https://koa.com/blog/30-vs-50-amp-rv-service/
Yes it is confusing,
I am not an electrician but the 30 amp service is 120 Volts
The 50 amp service is 240 volts or two 120 volt lines at 50 amp each
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