I still can't figure out how this is happening! I had done this exact same procedure couple weeks back so I thought I would document the procedure.I'm connected to a 20amp outlet in the garage., about a 30" heave gauge extension cord to the 50 amp cord.Walking into the Discover I see the EMS system drawing about 7 amps. I shutdown the charger & I'm not at 5ampsset both AC units to cool with the fan on auto.After a minute the #1 AC fires up & I see the amps spike to about 22 and then drop down to 10amps I hear the one compressor startup & the amps spike above 20amps for a second then drop down to 15 amps.OK, I climb up on the roof, only rear compressor (AC#2) running) I climb back down, drop the thermostat on AC 1 to 70 deg.Climb back on roof BOTH AC's fan AND compressor running. Back in coach BOTH AC's on & blowing cold EMS showing both AC's WITH compressors going drawing 17 amps. Looks like the EMS sheaded the HWH and Norcold fridge.Thanks

Something somewhere is wrong, call an electrician. Their is now way 20amps can run 2 Air conditioners.

Leave it on for a while and see what burns up first.

Need more info. Model numbers and brand of the roof AC units. What is the outside ambient temp where you are at. There are some RVP AC units that are lo amp draw units, about 11 amps with fan AT 95 DEGREES AMBIENT. For each drop in temp of 10 degrees the compressor will pull 1 amp less. SO, if your ambient is 75 degrees, those AC units will pull 9 amps each. Doug

One of the compressors isn't on. I have an 05 Fleetwood and I'm guessing we both have the Intellitec EMS. Did you select the 20A mode?Both ACs on is about 25-27A depending on the outside temp.

I don't know how 2 AC units could possibly run together on a 20 amp supply, even ignoring any other loads that could be on. If you are reading 15 amps on one, that'd be 2x15 = 30 amps.Have you got both AC units connected to the same leg of the 50 amp service? I thought they were normally split so each one is on a different hot leg, unless your units are done differently? Do you have specs on the AC units that will show what the normal full load current draw is (at 120 volts)?Regardless, what voltages are you seeing?

BOTH roof AC units running on a 20 amp power source?

39 Replies

NinerBikes
Explorer
Aug 24, 2014
myredracer wrote:
Ozlander wrote:
It takes a thread like this for people to state what they don't know about electricity.

And it also takes a forum like this for some to be negative or attack others or insinuate that they're smarter than everyone else. ;)

Smarter is a poor choice of words, perhaps more experienced in real world observations is a better choice. Judging by the tags on the AC units, it says 20 amps, per unit.

Going by the electrical code, running 2 AC units on a 15 to 30 amp adapter cord is the weakest link, regardless of if the outlet in the house or yard is 15 or 20 amps.
myredracer
Explorer II
Aug 24, 2014
Ozlander wrote:
It takes a thread like this for people to state what they don't know about electricity.

And it also takes a forum like this for some to be negative or attack others or insinuate that they're smarter than everyone else. ;)
Ozlander
Explorer
Aug 24, 2014
It takes a thread like this for people to state what they don't know about electricity.
dougrainer
Nomad
Aug 24, 2014
RV daytrader wrote:
OK...each compressor pulls 7.8 amps and each fan FLA is 2.9...that is the MAX they will pull. In real life those compressors will pull around 7 amps and the fans about 2 amps...on a real hot day the compressors will pull close to the max, but on a cool day the amp draw will be less....if started seperately I can see this happening....

No, there is NO MAX limit. Just as each 10 degrees ambient colder than 95 will pull 1 amp less, each 10 degrees ABOVE 95 will pull 1 amp MORE. Doug
AllegroD
Nomad
Aug 24, 2014
mchero wrote:
Kiwi_too wrote:
Big Katuna wrote:

BTW, a 20A breaker can support a 23-24A load for up to a minute.

I thought it only took seconds. After some reading I see it seems exponential. the higher the amps over rating the faster it trips. 30 amps, on a 20CB, would trip in seconds where 23-24 would take a minute. Thanks.

Id get the biggest cord I could find like contractors extension cords!

Stay away from the dollar stores!

Huh?
mchero
Explorer
Aug 24, 2014
Thanks for the post Gil. Good point.
myredracer
Explorer II
Aug 24, 2014
Looking just at the nameplate data for one AC alone, it tells you that you should not be adding any additional load onto an upstream 20 amp breaker. The 20 amp is sized to handle the unit's starting current (at nominal 120 volts).

If you look at the electrical code, you will find that for the two ACs and any other loads, you need use the overcurrent device for the largest unit (both 20 amps in this case) and the full load rating of any other loads to calculate the breaker in an upstream panel and wire size. Going by code, minimum wire size feeding two ACs and any other loads is probably going to be just over 30 amps, meaning #8 wire and a 40 amp or possibly 50 amp breaker.

And if the voltage drops causing the AC to draw more current, the situation only gets worse.
RV_daytrader
Explorer
Aug 24, 2014
OK...each compressor pulls 7.8 amps and each fan FLA is 2.9...that is the MAX they will pull. In real life those compressors will pull around 7 amps and the fans about 2 amps...on a real hot day the compressors will pull close to the max, but on a cool day the amp draw will be less....if started seperately I can see this happening....
mchero
Explorer
Aug 23, 2014
Kiwi_too wrote:
Big Katuna wrote:

BTW, a 20A breaker can support a 23-24A load for up to a minute.

I thought it only took seconds. After some reading I see it seems exponential. the higher the amps over rating the faster it trips. 30 amps, on a 20CB, would trip in seconds where 23-24 would take a minute. Thanks.

Id get the biggest cord I could find like contractors extension cords!

Stay away from the dollar stores!
MEXICOWANDERER
Explorer
Aug 23, 2014
Why does my 10.7 EER LG window air conditioner draw 4.87 amps @ 122 volts and a nearly three times larger rooftop AC unit draw merely twice that? Do they now have, say 13.6 EER rated roof air units for RV's? The LG is nasty R12