A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?

 
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Old 06-16-2011, 10:53 AM   #1
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A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Hey Guys,

I usually post in the Flooring section as Im a hardwood floor contractor, but Im doing some work in my own home.

Wiring a mini-split a/c and the manual says use a 14 awg & 20A breaker.

I ran about twenty feet of 14 awg exterior sheathed solid wire through conduit at the panel through the exterior wall and to the outside condenser unit.

...*then* I read "use a 20A breaker". Isnt code 12/20?

I thought I was going to use a 15A breaker until I read to use a 20.

Can I use a 20A breaker with this wiring?

This is the manual. See page #24 of the .pdf
http://us.lge.com/download/product/f...%29_011607.pdf

Can this unit operate on a 15A breaker?
See page #11 (first column unit LAN091CNP / LAU091CNP)
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Old 06-16-2011, 11:10 AM   #2
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


On average 14ga should have a 15A and 12ga should have a 20A breaker. In motor circuits the breaker sized can be adjusted for the motor instead of the wire.

In your case I would run the wire as 12ga and use the 20A breaker. The breaker is probably used for the startup current.

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Old 06-16-2011, 11:17 AM   #3
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Yeah I was hoping to avoid repulling.

Would the 14awg on a dedicated line be safe to use?
(20 feet, exterior sheathed, in a conduit)

I assuming LG knows what its unit can handle and what type of wiring is needed.
Is 12awg just being conservative?

Last edited by InterCounty; 06-16-2011 at 11:19 AM.
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Old 06-16-2011, 11:22 AM   #4
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Put the 15A breaker on the line to start with. See how the unit handles it. If it works well then leave it. If not, you may have to repull the line. Wait for a real sparky to show up here. 480Sparky will know the answer.
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Old 06-16-2011, 12:44 PM   #5
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Quote:
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................ Isnt code 12/20?............

No. There is no such thing as a single conductor having a single ampacity. Motors have their own set of rules (Art. 430), and they modify the "12/20" rule per 240.2(G).

There are cases where AWG 14 is legal on a 35a breaker. All you really need to look at is the nameplate of the unit... it will tell you the smallest wire size and the largest breaker allowed.
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Last edited by 480sparky; 06-16-2011 at 12:46 PM.
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Old 06-16-2011, 02:06 PM   #6
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


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Originally Posted by 480sparky View Post
There are cases where AWG 14 is legal on a 35a breaker.
I believe you, but under what conditions?

35A gives approx. (35A/15A)^2 = 5x the wire heating you'd get with 15A and so probably gives you almost 5x the temp. rise above ambient for the insulation.

I do not understand this.
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Old 06-16-2011, 03:21 PM   #7
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Motor circuits have there own protection.
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Old 06-16-2011, 03:29 PM   #8
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


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I believe you, but under what conditions?
Motors.

Quote:
Originally Posted by GettingBy View Post
35A gives approx. (35A/15A)^2 = 5x the wire heating you'd get with 15A and so probably gives you almost 5x the temp. rise above ambient for the insulation.
What the hell is all this gibberish?

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Originally Posted by GettingBy View Post
I do not understand this.
Electricians do. It's called Knowing the Code and Years of Experience.

See how electricical is NOT 'so simple a 12-year-old person of diminished capacity' can do it?
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Old 06-16-2011, 03:30 PM   #9
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Or a wise guy woodworker.....
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Old 06-16-2011, 04:20 PM   #10
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Quote:
Originally Posted by 480sparky View Post
Motors.

What the hell is all this gibberish?

Electricians do. It's called Knowing the Code and Years of Experience.

See how electricical is NOT 'so simple a 12-year-old person of diminished capacity' can do it?
Thanks, I'll scrounge through my '99 NEC on motors and Mullin's explanation of it.

Re: gibberish
I thought the ampacity of a conductor had to do with how hot the insulation gets, due to the ambient temp and wire heating.
The current squared and the wire gauge determines the heating in a length of wire.
So, the same wire carrying 35 amps dissipates 5x more watts than when it's carrying 15A.

Who are you quoting? I doubt there are 12 YO electricians at any level, high or low, of mental capacity.

Last edited by GettingBy; 06-16-2011 at 04:24 PM.
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Old 06-16-2011, 04:22 PM   #11
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Quote:
Originally Posted by GettingBy View Post
I thought the ampacity of a conductor had to do with how hot the insulation gets, due to the ambient temp and wire heating.
As well as the temperature rating of the insulation.... there's more than one. There's also temp. ratings of terminals, number of conductors in a cable/raceway, lots of stuff to consider.


Quote:
Originally Posted by GettingBy View Post
Who are you quoting?
The 12-y.o. remark? Some now-banned member who claimed electrical was so easy a 12-year-old retard could do it.
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Old 06-16-2011, 04:30 PM   #12
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


I guess if someone wanted to look it up for themselves, the NEC cluster hump would basically start with what is now Table 310.15[B],[16], then to 240.4[D], to 240 Table 240.4[G] then to Article 440 and I believe it probably ends at 440.4[C] with the required branch circuit rating and nameplate values in compliance with other sections of Article 440 that are to be provided by the equipment manufacturer.
I might be a concerned about estimated VD on motor or compressor branch circuits, so if it were going to be a long run for that #14, I would probably upsize to #12 instead just for the sake of the equipment.

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Old 06-16-2011, 04:42 PM   #13
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Quote:
Originally Posted by 480sparky View Post
As well as the temperature rating of the insulation.... there's more than one. There's also temp. ratings of terminals, number of conductors in a cable/raceway, lots of stuff to consider.

The 12-y.o. remark? Some now-banned member who claimed electrical was so easy a 12-year-old retard could do it.
Mr. 480sparky, I recommend "Verbal Judo", written by a cop who found a way to handle the daily insults these guys are paid to put up with.

Send this long-gone member to work on a commercial panel and see how long he lasts without being burned, blinded or killed.

Thanks, guys. I'll see if I can reconcile the rules with how I think physics works. Digesting this small chunk of the NEC over several sessions shouldn't give me too much heartburn.

Last edited by GettingBy; 06-16-2011 at 04:46 PM.
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Old 06-16-2011, 05:35 PM   #14
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


480 said it best. As another said you can try to run it on the 15 amp breaker and the most it will do is trip the breaker. Otherwise pull a 12ga instead, put it on a 20amp breaker and not worry about it.

As 480 said motors and their manufacturer have their own rule of thumb when it comes to wire size and amp draw. Type of wire and its installation will also make a difference too. Such as aluminum wire, copper wire, solid wire, different types of stranded wire and the insulation used around the wire all play a facter in the amp load it can carry.
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Old 06-16-2011, 05:43 PM   #15
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


What ever you decide to do....

IMO I'd install per manufacturers specs.
If you don't & have a warranty issue, this will give them some wiggle room to stonewall you on any issues.
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Old 06-16-2011, 05:46 PM   #16
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


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........motors and their manufacturer have their own rule of thumb when it comes to wire size and amp draw. ............
Not really a 'rule of thumb'. More like engineering and design protocols, as well as listing requirements. I doubt you'll find a couple engineers sitting in front of a huge computer monitor and have the following conversation:

"Hey, Fred, I'm working on a new compressor design. Do you think AWG 12 and 40 amps will work?"

"Hmmmm. Lemme see, Jim. Well, I see you're using a simple piston-style pump. I've seen those run just fine with number 14 on a 35 amp breaker."
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Old 06-16-2011, 06:15 PM   #17
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


wOw! Hyjack much?

Ok you guys fried my brain with all that elektikol hocus pocus string theory stuff.

Not to mention I'm an ELEVEN year old retard, so I should pick this all up next year.

So anyway............

Ignore what the manual says 14g & 20a and put a 15a in and wait to see if it trips?

OR

go with manufacturers recs and use the 14g & 20a

I'm inclined to use manufactures recs for warrantee issues.


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Or a wise guy woodworker.....
And yeah, I'll be sure to pick up all your wire clippings the next time you tromp all over my hardwood floor to install receptacles and switches.

...and put 'em in your truck
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Old 06-16-2011, 06:23 PM   #18
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Quote:
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..............Not to mention I'm an ELEVEN year old retard, so I should pick this all up next year..............
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Old 06-16-2011, 06:24 PM   #19
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


I am not an electrician, therefore I clean up after myself.
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Old 06-16-2011, 06:29 PM   #20
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Re: A/C Wiring Manual Says 14 Awg & 20 Amp Breaker?


Quote:
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I am not an electrician, therefore I clean up after myself.
I thought you meant I was the wiseguy woodworker

...I see you know what I mean about those messy electricians!


...oops did I say that here?


Last edited by InterCounty; 06-16-2011 at 06:31 PM.
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