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Old 12-07-2019, 12:30 PM   #1
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50 Amp Service Query

I am shopping for a late model Airstream and have a question.

If the trailer has 2 factory installed AC units, does it automatically have 50 amp service? (The "window sticker" says 30 amp service and in the options section there is reference to 2nd A/C install but no reference to 50 amp service.)

Thanks!

Randale
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Old 12-07-2019, 03:03 PM   #2
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Originally Posted by randale View Post
I am shopping for a late model Airstream and have a question.

If the trailer has 2 factory installed AC units, does it automatically have 50 amp service? (The "window sticker" says 30 amp service and in the options section there is reference to 2nd A/C install but no reference to 50 amp service.)

Thanks!

Randale
Welcome to the forum.

Unless somebody somewhere did something very wrong, it should have 50 amp service. If you look at a photo of the front of the trailer, a 30 amp trailer will have a power inlet left-center, just below the front window.
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Old 12-07-2019, 03:41 PM   #3
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2 A/Cs require 50Amp Service

Each A/C - Heat pumps each use about 12-14 Amps, The electric mode of the water heater 10 amps, the refrigerator about 4 amps and converter 3 amps. The A/Cs do not share the same line of the four wire 50A (2 line-50A each, 1 common, 1 ground) service so its not possible for it to be wired 30Amp and have it work. Here are a couple easy ways to quickly confirm 50Amp service.

1) look at the service connect on the outside of the trailer. If it has slots for 4 prongs it is 50A, three slot plug is 30A (1 line, 1 common, 1 ground)

2) Run both A/Cs and the hot water heater in electric mode (switch in the bathroom) at the same time, if it all works, you are good to go. An internet search will show you the common plug types. Only welders and older electric ranges use an ungrounded connections. Code requires RV's to have grounded connections (for GFI protection).

Hope this helps.
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Old 12-07-2019, 07:25 PM   #4
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Hi

Depending on the mode they are operating in, the temperature, the humidity, and what you have it set to ..... the current draw on the HVAC units can vary. You will see anything from 12A up to 16A in "run" mode. A pair of units both pulling 16A would overload a 30A power post.

All that's not based on some spec sheet. It's based on actually measuring what my units actually pull while in operation.

Bob
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Old 12-07-2019, 09:48 PM   #5
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Unless somebody did a hack job, it is 50 amp. Check the breakers of the electrical panel. You will see two 50 amp breakers.
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Old 12-08-2019, 06:36 AM   #6
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Out of curiosity, I had a look at my old window sticker and it says the same thing. It lists the standard features including 30 Amp service then lists the additional heat pump as an add on without ever mentioning directly 50Amp service.
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Old 12-08-2019, 06:57 AM   #7
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You cannot start two AC’s with a 30 amp service. If factory, two AC’s always come with “50 amp” service. Remember that 50 amp actually gives you two 50 amp legs, for 100 amps total system capacity
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Old 12-08-2019, 07:26 AM   #8
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Running two A/C off 30Amp service

FYI, I am often able to run both my 13,500 BTU units from a 30 Amp service disconnect and a 30 to 50 amp adapter. I do have to run both the water heater and refrigerator off propane, the batteries must be fully charged, and I have to leave the entertainment devices off and only use the led lights. In practice my heat pumps draw 12 amps each at 125 V and modest outside temperatures / humidity and 16 amps at 110 V with high temperatures and humidity, so it is close to the limit.
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Old 12-08-2019, 07:58 AM   #9
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Thanks to everyone for the great answers!

Randale
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Old 12-08-2019, 08:39 AM   #10
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You cannot start two ACís with a 30 amp service. If factory, two ACís always come with ď50 ampĒ service. Remember that 50 amp actually gives you two 50 amp legs, for 100 amps total system capacity
Not true.
50 amp service is 50 amp service. 30 amp+20 amp =50 amp. You don't add 2+2 and get 22.
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Old 12-08-2019, 08:56 AM   #11
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Actually, Brick1 is correct. 50 Amp service includes two 120 V single phase lines each rated for 50 Amp. Since the two lines remain isolated and because at the service disconnect they are often wired to the same phase, 240 V is not generally available but RV's don't use it anyway. The common return is rated for 100 Amps. At the Breaker there are two 50 Amp breakers one each on the isolated circuits so 100 Amp total as Brick1 indicated.
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Old 12-08-2019, 09:05 AM   #12
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Yes, 50 amp service has two 50 amp legs. 50 amp service provides over 3 times the available power of 30 Amp service.

The trailer with 2 AC's certainly should have 50 amp connections.
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Old 12-08-2019, 10:54 AM   #13
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50 amp not mentioned on my "window sticker" either. I have two AC/Heat Pumps and 50 amp service in my trailer.

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Old 12-08-2019, 11:08 AM   #14
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Quote:
Originally Posted by randale View Post
I am shopping for a late model Airstream and have a question.

If the trailer has 2 factory installed AC units, does it automatically have 50 amp service? (The "window sticker" says 30 amp service and in the options section there is reference to 2nd A/C install but no reference to 50 amp service.)

Thanks!

Randale
.......2 ACís, You get 50amps. Good choice
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Old 12-08-2019, 05:17 PM   #15
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If your service is experiencing marginal performance you might beat the problem by using Microair's EasyStarts on you unit. The overall A/C performance would be greatly enhanced.
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Old 12-09-2019, 10:48 AM   #16
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Not true.
50 amp service is 50 amp service. 30 amp+20 amp =50 amp. You don't add 2+2 and get 22.
...each leg is 50 amp.....2 legs of 50 amp each.....30 is just 30 amp
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Old 12-09-2019, 10:56 AM   #17
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I'm not piling on, really.....

Quote:
Originally Posted by overlander63 View Post
Not true.
50 amp service is 50 amp service. 30 amp+20 amp =50 amp. You don't add 2+2 and get 22.
30A service is 120V/30A single phase.

50A service is 120/240V 50A. Each of the 120V legs has 50A capability. Either line measured to neutral is 120V. Line to line is 240V. Nothing in any Airstream I am aware of runs line to line, but there is 100A capability at 120V.

Al
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Old 12-10-2019, 06:34 AM   #18
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Hi

Just to complete this out:

With 50A the two hot lines are 180 degrees out of phase. Neutral current when fully loaded will be zero ( the two 50A loads currents will sum to zero at the neutral). This is a good thing since the wire and connection pins on the neutral are only rated to 50A. Bottom line is that even though you don't *use* 240V in the trailer, the circuit needs to be fed with 240V ....

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Old 12-10-2019, 08:15 AM   #19
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Bob,

If not fed with 240, then the current available is only 50A so shouldn't be a problem, right?

Same situation as if the loads on the one phase are not in use - i.e. second AC.

Al
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Old 12-10-2019, 10:52 AM   #20
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Originally Posted by uncle_bob View Post
Hi

Just to complete this out:

With 50A the two hot lines are 180 degrees out of phase. Neutral current when fully loaded will be zero ( the two 50A loads currents will sum to zero at the neutral). This is a good thing since the wire and connection pins on the neutral are only rated to 50A. Bottom line is that even though you don't *use* 240V in the trailer, the circuit needs to be fed with 240V ....

Bob
You're right Bob, it was wrong of me to state that neutral back to service has 100 Amp capacity; it does not. Furthermore you are correct to imply that the service connections are not properly wired where both lines are to the same 120V bus. In reality that would be a serious code violation. So my mistake, thanks for the correction.

I remember now that it is when using 50A service from 120V Generators that both leads have the same phase and the total limit is 50A.

Thanks for the correction.
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