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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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#49 · (Edited)
You can run 35 amps through 14 for several months before bad things will start to happen.

Wire will not suddenly explode when 0.00001 amps more than it's NEC ampacity is induced. You won't start a fire by running 20.000001 amps through #12.

One thing you don't want to do is upsize the wire just to give yourself a warm and fuzzy feeling, then simply match the breaker to that wire size. You may end up with a breaker that's oversized for the load.

Many times, especially in commercial and industrial, over-sized breakers and wire are installed to the load, then another breaker (or fuses) are used to protect the load itself. This is usually done to limit voltage drop. It wouldn't be uncommon to see, say, #2 on a 100a breaker going to an RTU, then 60a fuses used in the service disconnect.

But in the case of putting 14 on a 35 amp breaker, keep in mind there's thousands, if not tens of thousands, of hours of research and testing by a multitude of qualified people that went into figuring that out. It wasn't a case of Skeeter and Bubba goofing around one day after shop class. Skeeter: "Hey, Bubba, let's see what happens to this wire when we overload it!" Bubba: "Hmmmm. Nothing. Well, I reckon number fourteen is good for thirty five amps..... Imagine that!"

Another thing to remember about the 14/35 thing: It's a motor load. The 35a breaker is allowed because that's what it takes to start the motor. It doesn't run and draw 35 amps.... more likely it runs at 6-10 amps.

So what problems will result with running 20-30 amps through #14? Not much in the short term. If there's a problem that would create that situation, most likely it will be noticed and corrected & life will go on. And you'd be hard pressed to find a fault that would consistently cause that precise of a current flow.

If there's a fault that would draw more than 35 amps, well, the breaker size at that point is moot. A short will (or at least should, if everything is coordinated correctly) trip any size breaker..... 5 amps to 5000.
 
#51 ·
No the insulation will spontaneously combust. Seen it happen. It opens up a portal to another dimension via the gamma ray burst resulting from such rapid combustion. The resulting vacuum created from said combustion will suck you in to the 5th dimension that exists in parallel with our own convoluted multiverse. At least that's what Skeeter and Bubba told me.

--

I think it's really a function of what the insulation is. Maybe it gets brittle, maybe it just gets soft and slowly melts. Could eventually catch fire. Hell maybe there's a kink in the conductor and that burns up the line ahead of time. If the dielectric (insulation) is strong enough, then it gets back to the physical properties of the copper itself. If it's aluminum then you're just f'ed no matter what.
 
#57 · (Edited)
......... Yup its true code mandates 14 on 15 a breakers and 12 on 20 a breakers. .........

Ya got a Code reference for that?

..... Code be what it may calculations say 14 gauge will tolerate 20 a pretty darn well. Its closer to 30 a when that wire will start gettin red hot and the local fire department will come over for a visit.........
You need to go back to school....if you ever went in the first place you got robbed.
 
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#59 · (Edited)
AWG gauge Conductor 14 Diameter Inches Conductor 0.0641 Diameter mm 1.62814 Ohms per 1000 ft. 2.525 Ohms per km 8.282 Maximum amps for chassis wiring 32 Maximum amps for
power transmission 5.9 Maximum frequency for
100% skin depth for solid conductor copper 6700 Hz

If a short run of 14 maxes out at 32 a. Then a long run of 14 I would expect to get warm to the touch fairly quickly at 30 a. As distance = resistance. How many amps do you think it can pull before you stick a match on it? Thnx
Yadda yadda yadda. Copying and pasting a bunch of gobbeldygook from another website means nothing.

Again, you got a code reference for your 15a/14AWG and 20a/12AWG claim?
 
#61 ·
"If a short run of 14 maxes out at 32 a. Then a long run of 14 I would expect to get warm to the touch fairly quickly at 30 a. As distance = resistance. How many amps do you think it can pull before you stick a match on it? Thnx"

The insul. temp at a point on a wire depends only on I squared, the thermal resistance of the insulation, convection, conduction and radiation losses. The total wire length determines the total heat loss. See the Neher-McGrath equation.

For the melting point of wire in free air see the Onderdonk/Preece equation.
 
#62 ·
I suppose InterCountry has installed the system and moved on since his 6/16/2011 post but he did bring up a lot of good comments.

The manufactures nameplate dictates what size breaker to install but I doubt if it states the wire size. The OP sent us a copy of the installation manual not the nameplate.

Since the manual seems full of typo's I wonder if the #14 was just someone taking journalistic liberties.

Overcurrent protection is designed to protect the feeder or branch circuit wiring. If a manufacturer needs better overcurrent or overload protection for their equipment they usually put it inside the equipment.

The only reason I can figure a manufacturer would demand smaller wire than the OCP would be to make their equipment more attractive (money) than their competitors. But, it would have to be on the nameplate, per Code.

Good Luck from Columbiana, Alabama
Maurice Turgeon, http://thesemi-retiredelectrician.com
 
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