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Old 11-21-2013, 03:05 PM   #1
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12 gauge romex

I am fixing to run the electrical wires for a second a/c that i will be installing early next year. The hardest part is running the wire through the ceiling. I have plenty of 12-2 yellow romex from other projects my neighbor did. Will this be okay to use? I will install a a coleman 13500 btu that only draws 14 amps max.
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Robert
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Old 11-21-2013, 03:55 PM   #2
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12ga would be appropriate for this application. I like to pull a piece of construction line first, and then pull the wires. I also like to keep the construction line in the wall/ceiling just incase I need to pull something else later.
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Old 11-21-2013, 04:13 PM   #3
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12ga would be appropriate for this application. I like to pull a piece of construction line first, and then pull the wires. I also like to keep the construction line in the wall/ceiling just in case I need to pull something else later.
X2
12 ga is good up to 20amps
14 ga is good to 15 amps.

12 ga is a little stiffer to work with, but will be fine.

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Old 11-21-2013, 04:52 PM   #4
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It is true that 12 AWG Romex building wire is rated for 20 amps and 14 AWG is rated for 15 amps. That said, depending upon the length of run and other factors that rating may be reduced.

Length of run within a travel trailer is not going to be a problem, but the length of the run from the power source (power pedestal at a campsite, perhaps further at home) needs to considered when choosing the appropriate wire size/gauge. Long runs = voltage drop. Voltage drop = higher current. Higher current = bad for air conditioning unit motors.

Proper wire size selection generally applies an 80% load factor for continuous loads. The 14 amps mentioned is 70% of the #12 AWG wire so normally that would be fine. That said, given the likelyhood of a long run from the power source and the possibility of low voltage at that source, for this application the #12 AWG wire selection may be a bit marginal. With the wire length needed within the trailer it won't cost much more to run #10 AWG wire. That wire size will reduce any low voltage worries almost to zero and may help with the efficiency and service life of your new A/C unit.

Using #10 AWG wire doesn't mean that you need to upsize everything to 30 amp service. The normal 20 amp connectors can still be used. The #10 AWG wire within the trailer is just to help eliminate voltage drop worries.

FWIW. vic
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Old 11-21-2013, 05:24 PM   #5
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I'm no electrician, but something doesn't sound right with that Coleman 13500 only drawing 14amp.

Doesn't 14a x 120v = 1680 watts? If so why won't a single Honda EU2000i start and run the AC on my TT? I thought the Honda 2k surged to 16Amps and Sustained 13Amps. My Honda won't start my Coleman 13500 AC which leads me to think the AC required for than 14Amps max.

You guys are all much better at this stuff than I am, what am I missing?
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Old 11-21-2013, 05:44 PM   #6
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Originally Posted by clubhouse View Post
I'm no electrician, but something doesn't sound right with that Coleman 13500 only drawing 14amp.

Doesn't 14a x 120v = 1680 watts? If so why won't a single Honda EU2000i start and run the AC on my TT? I thought the Honda 2k surged to 16Amps and Sustained 13Amps. My Honda won't start my Coleman 13500 AC which leads me to think the AC required for than 14Amps max.

You guys are all much better at this stuff than I am, what am I missing?
The startup current of a motor can be many times higher than the running current. The start condition is often referred to as "locked rotor current".

A running motor depends upon the impedance created by back EMF related to the expanding and collapsing fields of the iron and motor wire windings to limit current. At startup the voltage rushes in and until the rotor begins to turn the current is only limited by the (DC) resistance of the motor windings. That in-rush current is close to a dead short.

Your small generator doesn't have enough capacity to provide the power needed to get the rotor turning so the locked rotor load suppresses the voltage. The result is that the rotor never turns fast enough and the generator continues to see a dead short.

If you could somehow get the air conditioning motor spinning first, then your small generator would likely be able to keep the motor running.

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Old 11-21-2013, 06:19 PM   #7
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I'll bet my 13,500 BTU A/C unit is wired with 14 ga wire.

12ga wire will be fine for your installation with some margin to boot.

How to wire 13,500 BTU RV AC. 14ga wire or larger
http://www.ehow.com/how_7871789_wire...l-trailer.html

Doug
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Old 11-21-2013, 06:27 PM   #8
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Wire size calculator.
14 amps up to 40 feet run = 14ga
So you will have some margin with 12ga.

http://www.csgnetwork.com/wiresizecalc.html

FYI,
Doug
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Old 11-21-2013, 07:08 PM   #9
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Originally Posted by VicS1950 View Post
The startup current of a motor can be many times higher than the running current. The start condition is often referred to as "locked rotor current".

A running motor depends upon the impedance created by back EMF related to the expanding and collapsing fields of the iron and motor wire windings to limit current. At startup the voltage rushes in and until the rotor begins to turn the current is only limited by the (DC) resistance of the motor windings. That in-rush current is close to a dead short.

Your small generator doesn't have enough capacity to provide the power needed to get the rotor turning so the locked rotor load suppresses the voltage. The result is that the rotor never turns fast enough and the generator continues to see a dead short.

If you could somehow get the air conditioning motor spinning first, then your small generator would likely be able to keep the motor running.

vic
Thanks. You first paragraph is what I always understood, and that is what got me thinking about the OPs original question and wondered if that temporary start up current would require heavier guage wire.
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Old 11-21-2013, 07:15 PM   #10
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12 gauge romex

Thanks everyone. Just wanted to be sure before going through all the work of running the wire.
Clubhouse don't know about generators but here is a screen shot of the unit i will be installing.
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