Please check my (electrical) math - Fiberglass RV


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Old 05-03-2018, 10:32 AM   #1
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Please check my (electrical) math

Background - I am adding an electrical outlet to my 1997 Scamp 13 in conjunction with installing a removable window AC unit. I noticed that the 3-way Dometic refrigerator is wired in series with the existing 120v outlet next to the sink and wondered if this could cause a problem.
My Dometic owner's manual states that the heating element is rated at 125 watts. Assuming single phase AC power, using a power factor of 1, that works out to 1.04 amps (125/120). Which seems like a very low number for a refrigerator?
On 12 volts DC, the draw is 10.4 amps.
If the fridge really is drawing less than 2 amps, I'll just leave thing the way they are. I'm a new Scamp owner and have only taken one 6-week trip in this unit where I had several things plugged into the 120 v outlet via an outlet strip - fan, computer, table lamp, computer speakers, phone charger. No problems experienced with hot-feeling wires, etc.
Thanks.
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Old 05-03-2018, 10:36 AM   #2
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Yes, 1 amp draw at 110 volts AC (or 10 amps at 12 volts DC) sounds about right. That's what my Dometic 3 way refrigerator draws.
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Old 05-03-2018, 11:37 AM   #3
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Nigel,

Our Casita had a 4 cu ft Dometic RM2454. It drew 1.5 amps on 120VAC.
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Old 05-03-2018, 11:50 AM   #4
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surely, you mean the outlet is wired in PARALLEL.

and yeah, 125 watts sounds about right for an absorbption fridge. 10 amps at 12V is the same 120 watts as 1 amp at 120V.
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Old 05-03-2018, 02:53 PM   #5
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Originally Posted by John in Santa Cruz View Post
surely, you mean the outlet is wired in PARALLEL.
Not that it matters, but if it was wired in series, then it would only work when something was plugged into the the other outlet, and that something would have to draw lots of power, (low resistance). A heater maybe. Neither would work as designed as they would be sharing the total voltage.

The fridge would then work best if the other plug was a dead short.
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Old 05-03-2018, 03:01 PM   #6
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Depending on the BTU rating of the AC unit, you may or may not be able to run it on the same circuit as the fridge. A 5000 BTU AC is probably in the 6-7 amp load range (check the specifications for your AC unit). Starting should not be an issue as a typical circuit breaker is a thermal type designed to take a momentary overload, however, bear in mind that they are rated for 80% of full load rating for long delay times. Minimum circuit breaker size for household wire is 15 amps. 15 amps times .8 is 12 amps which is the maximum load. That being said, you should have no issue running the fridge and a 5000 BTU AC unit on the same circuit. A 8000 BTU unit puts you in the questionable range. Hope this helps.
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Old 05-03-2018, 08:10 PM   #7
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Well .. in series means one after another in a daisy chain fashion, and the hot is wired in series, the neutral is wired in series, and the ground is wired in series.

Confused yet?

If so then follow the flow of electrons.. they don't have to go along the daisy chain.
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Old 05-04-2018, 01:35 AM   #8
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Originally Posted by gordon2 View Post
Well .. in series means one after another in a daisy chain fashion, and the hot is wired in series, the neutral is wired in series, and the ground is wired in series.

Confused yet?

If so then follow the flow of electons.. they dont have to go along the daisy chain.
In all 120VAC wiring the neutral line go to all neutral terminals and the hot line goes to all hot lines. The safety goes all the green terminals. No SERIES to it, all Parallel.
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Old 05-04-2018, 01:40 AM   #9
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Quote:
Originally Posted by nigeleccleston View Post
Background - I am adding an electrical outlet to my 1997 Scamp 13 in conjunction with installing a removable window AC unit. I noticed that the 3-way Dometic refrigerator is wired in series with the existing 120v outlet next to the sink and wondered if this could cause a problem.
My Dometic owner's manual states that the heating element is rated at 125 watts. Assuming single phase AC power, using a power factor of 1, that works out to 1.04 amps (125/120). Which seems like a very low number for a refrigerator?
On 12 volts DC, the draw is 10.4 amps.
If the fridge really is drawing less than 2 amps, I'll just leave thing the way they are. I'm a new Scamp owner and have only taken one 6-week trip in this unit where I had several things plugged into the 120 v outlet via an outlet strip - fan, computer, table lamp, computer speakers, phone charger. No problems experienced with hot-feeling wires, etc.
Thanks.
Your math is correct. The only error I see is the term series. All 120 vac outlets and devices are connected in parallel. Your's are too.
As for all the stuff you have connected to only outlet. None of them draw much current. So every things good.
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Old 05-04-2018, 07:45 AM   #10
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Originally Posted by Byron Kinnaman View Post
In all 120VAC wiring the neutral line go to all neutral terminals and the hot line goes to all hot lines. The safety goes all the green terminals. No SERIES to it, all Parallel.
Alas, you missed my point. It is of course a parallel circuit, but there is a "series to it" and this can cause confusion. The neutral wires are connected in a series, one after another. Same for the hot and the ground. So my point was that this is a reason why someone might get the terms mixed-up. If one understands this point of confusion, one is better able to explain the terminology.

My other point was if someone is not sure to call it a series or parallel circuit...
Quote:
Originally Posted by gordon2 View Post
...
...then follow the flow of electrons.. ...
In series circuit there is only one route and they have to go along the entire length of the daisy chain, though the wires and loads both. In a parallel circuit, there are parallel routes.
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Old 05-04-2018, 09:54 AM   #11
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OK, thanks for the advice and for correcting my series-parallel mistake. I'm leaving the fridge wired as is, and adding an extra breaker wired to a new outlet in the wall of the dinette bench. I'll plug the removable window unit into that. And FYI, the AC will be held in place by one of these A/C Window Mount Design for Scamps
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