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A/C wiring manual says 14 awg & 20 amp breaker?

17K views 66 replies 16 participants last post by  SemiRetiredEL 
#1 ·
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/file/1000001401/LA091CNP_LA091HNP_LA121CNP_LA121HNP_Service_Manual_%283828A20926C%29_011607.pdf

Can this unit operate on a 15A breaker?
See page #11 (first column unit LAN091CNP / LAU091CNP)
 
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#2 ·
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.
 
#3 · (Edited)
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?
 
#4 ·
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.
 
#5 · (Edited)
................ 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.
 
#17 ·
wOw! Hyjack much?:w00t:

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.




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 ;) :thumbup:
 
#12 · (Edited)
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,[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.
 
#14 ·
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.
 
#16 ·
........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."
 
#19 ·
I am not an electrician, therefore I clean up after myself.
 
#22 ·
While I was doing a cabinet/mantle install the electrician showed up and was going to put in some recessed cans. He opened the ceiling and cut some round holes using a sheet rock saw (what, no hole saw WTF). We ended up picking up a bunch of wire cutoffs at the end of the day that made it past our tarps and onto the wood floor.. I just don't get it. Wear a small pouch and put the trash in there. What is so hard?
 
#28 ·
No I didn't, I just didn't mention it. I did mention it in one of my other posts though. ;)
 
#31 ·
Not talking about the wire, talking about the motor itself.
 
#32 · (Edited)
IMHO,

That kinda' goes to the heart of this matter. The wire temp. rise, among other things, determines safety.

You could put 20 A @ 60 Hz through #14 copper romex and measure the wire insulation temperature rise above ambient with a thermistor or thermocouple. You could embed the wire in a wall to get a more real-life reading.

The wire does not know how come the 20 A is flowing. It doesn't know if there is a motor, a 442 uF capacitor or a 6 ohm resistor connected to it.

I followed
Table 310.15,
[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.

with all the ifs, ands and buts. It's like doing your income tax.
I assume when you're done you've got a safe install per the NEC.

BTW, I think the NEC could be reduced to a computer program on a CD.
The program would ask you many questions which you answer, it would interpret your answers against a current copy of the code with all the ifs, ands and buts and then tell you how to do the job, step by step.
You would still need to be an electrician, the least reason being that the wording used in the questions asked and the answers given would have special meanings to electricians.
 
#34 ·
Well think about this then. In a 3 phase system you have 3 hots 1 ground and 1 neutral. If you use the three different phases for the lower voltage by using the neutral as the return wire (3PH 208vac going off a hot and neutral will result in 120vac) you will have 3 return currents traveling through the neutral. That means if you have a 20A circuit and are drawing full load on all of them the neutral wire is actually carrying 60A worth of current. But because the phases are different they cancel some of each other out and never heat the wire more than 20A worth of current would.

This is the same thing with the motor. The current traveling through the motor is the same as it is traveling through the wire. It doesn't magically readjust its phase relationship with the voltage when it leaves the motor. The load determines what is flowing through the wire, not the wire. The only time the wire determines how the flow of current is is when it reaches a resistance level that affects the current or it melts and stops the current.
 
#46 ·
Although, according to the NEC, if you utilize two of the phase conductors and the neutral conductor of a 3-phase 208 Wye system as multiwire circuits, the neutral current is 1.73 times the phase current.
The NEC made some changes to the requirements for feeder and service neutral calcs and raceway fill for these systems several code cycles back.
 
#36 ·
I guess I misunderstood you. I thought you said while it was in the wire the voltage and current were in phase and when it was in the motor there was a shift.
 
#40 ·
I did.
If you have a resistor (the wire), an inductor (the motor) and a capacitor all in series, and you use the current as a reference, then the voltage is in phase in the resistor, 90 degrees ahead in the inductor and 90 degrees behind in the capacitor.
If you use the voltages as references then it will seem like the current is changing phase in each component.
Since the current is the same in all parts of a series circuit I think it's better to use the current as the reference, which means you take it to be at zero degrees.

You need a two channel scope to see this.
 
#37 ·
What a Fri%%ing run-around here on a simple question- I can't believe it goes this far- That is WHY I stated the rule of thumb is 12 awg for 20 amps.... period.... Forget about that garbage................. I think some of you need to take a step back------ and simplify your thinking !!!!........................
 
#47 ·
Makes sense. Square root of three and all. Do they require an individual conductor for each neutral in a 120VAC circuit feeding off of a 3PH system now?
 
#48 · (Edited)
While I'm fully aware of why it's sometimes it's up to code due to the type of load, I'd personally put it on 12 for a reason. The breaker is there in case something goes wrong. What happens when the motor seizes up, maybe fries some parts and becomes a resistance load?

While it's not likely, and it's only a 5 amp difference in this case - what about the case 480 was talking about where it's ok to put 14 on a 35A breaker?

And whoever said something about carps giving bad advice burning down someones house - how exactly does suggesting that when in doubt, use wire you KNOW is rated for the breaker going to burn someones house down? I hope you were talking in general of the carps!

Lets say code lets you get away with something that normally wouldn't be cool under certain circumstances - like 2x4 joists, and an electrician comes on and says yeah, but you might just want to use 2x6's anyway just to be safe. I'd never fault someone for suggesting going above and beyond - even if it would be up to code either way.

On that note, I've seen carps do some really dumb stuff with electricity. I lit stuff up for a couple of years - not enough to be fully qualified electrician, but plenty enough to know when it's time to call one :)
 
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