A/C off of 20 amp service?

[Michigander]

Has anyone ever heard of a single a/c unit not being able to start and run on a 20amp shore power circuit? We bought a new coach and the dealer says don't run a/c unless connected to a 30 amp service or connected to the gen. They say it will cook the compressor. We have always run a/c units in trailers or coaches off a 20 amp circuit without a problem when at home so I am perplexed about what I am missing?? Thoughts?

[Effy]

Yes, I do it all the time. Worst case it will trip a breaker.

[time2roll]

pianotuna wrote:
#12 voltage with a 311 watt load was 119.1
#10 voltage with the identical load was 121.

Need second test with real 1500 watt load.

[DrewE]

pianotuna wrote:
Hi,

I recently compared a #12 100 foot extension cord to a #10 100 foot extension cord on the same 15 amp shore power outlet. The same dog bone adapter was used with both--but obviously in two different places.

#12 voltage with a 311 watt load was 119.1
#10 voltage with the identical load was 121.

So monitor voltage carefully--and consider getting an autoformer.

Based on these tablesl, the difference in resistance between 12 gauge wire and 10 gauge wire is 0.589 ohms per 1000 feet. In your test, you have 200 feet of wire to account for (100 feet coming and 100 feet going), and a test current of about 3 amps, so the voltage difference attributable to the change in wire should be about 0.3 volts. Obviously something else is different--maybe the plugs made better or worse connections, or maybe the voltage at the outlet varied a little between the trials, or maybe the 12 gauge cord has a poor connection at one of its ends.

[pianotuna]

Hi,

I recently compared a #12 100 foot extension cord to a #10 100 foot extension cord on the same 15 amp shore power outlet. The same dog bone adapter was used with both--but obviously in two different places.

#12 voltage with a 311 watt load was 119.1
#10 voltage with the identical load was 121.

So monitor voltage carefully--and consider getting an autoformer.

[427435]

I routinely run my Winny basement air conditioning on a 20 amp circuit and an extension cord. I suspect your Winny has a load control panel similar to mine. Just be sure to set it for 20 amps before turning the AC on. Otherwise, the 2nd AC unit will try to start and blow your house breaker.

[CA_Traveler]

DownTheAvenue wrote:

CA Traveler wrote:
20A is definitely borderline because of the smaller wiring.

I'd be cautious about running a 15K BTU A/C on 20A.

This post makes no sense. The A/C circuit inside the RV will be a 20 amp circuit wired with a 12 gauge wire and a 20 amp circuit breaker.

What's the difference?

OK but the OP referred to 20A shore plug which will also have the smaller wiring with the additional voltage loss vs a 30A or 50A plug. Plus the OP referred to a 20A home plug.

It's very typical that the problem is not the rig wiring but the voltage drop at the pedestal due to the 20A plug/wiring.

[full-timer]

I found out that running a single a/c unit and making sure the water heaters electric is turned off you will have no problem. Its when the water heater comes on that it will kick the breaker.

[time2roll]

DownTheAvenue wrote:

CA Traveler wrote:
20A is definitely borderline because of the smaller wiring.

I'd be cautious about running a 15K BTU A/C on 20A.

This post makes no sense. The A/C circuit inside the RV will be a 20 amp circuit wired with a 12 gauge wire and a 20 amp circuit breaker.

What's the difference?

Depends on the length of the wire in the circuit. Could be 150+ feet depending on conditions. This is why I recommend to check voltage in the RV once running.

[time2roll]

Keep the fridge and water on propane only, battery needs to be full charge.
Then let it rip. Do watch voltage is 108+ once the compressor is running smooth.

20 amp could be a generic name for 15 amp or 20 amp circuit so do verify what you have available. Also common to be a shared circuit so other items need to be off.

[Michigander]

Old coach was Sightseer 35J, New coach is 2016 Sunstar 31BE.

[DownTheAvenue]

CA Traveler wrote:
20A is definitely borderline because of the smaller wiring.

I'd be cautious about running a 15K BTU A/C on 20A.

This post makes no sense. The A/C circuit inside the RV will be a 20 amp circuit wired with a 12 gauge wire and a 20 amp circuit breaker.

What's the difference?

[Tom_Barb]

Ours simply kicks the Breaker off.

[CA_Traveler]

20A is definitely borderline because of the smaller wiring. But everything depends upon your A/C draw, other rig draws and the actual voltage.

I'd be cautious about running a 15K BTU A/C on 20A.

[Up_DownDeCoast]

This is going to depend on the size of the A/C unit. If your talking about the rig in your signature (which i also have)you should have no problem. I run one A/C unit when getting ready for a trip or doing maintenance at home. I actually plug into a 15 amp circuit. One of my units pulls about 12 amps. I make sure nothing else is running on that circuit when the A/C is on.

[AllegroD]

Sounds like a fair warning, though not fully explained. Depending on the draw and if other things are on a 20amp gang, you might be warned to monitor your power. Get a Kill-A-Watt or volt meter to monitor your 120 voltage. Read your AC manual. Less than 105volts on most AC will cause cumulative heat damage to your AC. This does not show right away but will take years of your AC life. I do not like going below 108 volts.