Can I install a 12-2 nmc cable to an AC that has a min circuit ampacity 22amp on a 30amp breaker. The AC draws about 17amps. The 22amps is at 125%.The name plate states the 22amp min circuit ampacity and a maxium 30 breaker.
2002 NEC
310.16 12cu 60c 25amps with*
*240.4d 12cu only 20amps unless permitted in 240.4e through 240.4g
240.g permitts AC article 440 parts III, VI
440.22a Rating or setting 175% branch circuit

[This message has been edited by abode electric (edited 01-08-2003).]

i would run at least 10 gauge wire. 12 gauge is only good for 20 amps, also AC is considered a continous load and 80% rules apply here. Other things to consider are voltage drop and ambient temperatures which also mean derating. With these other factors you may even have to run #8s.

[This message has been edited by spyder (edited 01-08-2003).]

Spyder,
(1)310-16 12cu 25amps
(2)240.40d allows higher than 20amps on 12cu
(3)AC isn't considered a continous load, it's a motor load, 125% of motor load. 17 amps X125%= 22 amps
(4)voltage drop and ambient temperatures are not factors here
I haven't found a reason why I can't do this. I know this may not be the best way but it complies with the code.

The 15, 20 and thirty amp limitations on #14, #12 and #10 wire do not apply to motor and air conditioning loads. Per the sections Dan quoted #12 looks acceptable.

<copied and pasted from the holt forum >

Remember the code is just minimum standards, you can always do better.

abode,

Your "code loop" seems valid, but as spyder said, the NEC is a minimum standard.
Considering voltage drop, especially during compressor start, (what's your LRA?) I'd run #10.



[This message has been edited by Redsy (edited 01-09-2003).]

abode electric

You said voltage drop not a factor so the run must be short. Unless you got couple of hundred to do, how much are you going to save buy using #12. Plus anyone that goes into the panel after you is going to ask questions on this, I am thinking "Home inspectors" or the GC who thinks he knows that 30 amp breakers need #10s

I wouldn't normally run a #12. The hvac guy didn't have his compressor on the job and told me it was a smaller unit. When it came to final inspections the inspector said I wasn't compling with the code. I knew the #12 I already ran meets code requirments of this unit. Why should I have to take that out and run a new one? There is sheetrock already in place.

Let's aproach this from another view.
THe local AHJ stated "non compliance".
Did he state a NEC Article??
We have to in NJ to make it a valid "Fail".

Now that I said that...
THe AHJ usually has the final word, unless you have an appeal process. If you do, then you have to "win" the Appeal. This usually takes time...(Time + Money)

You also probably will have future dealings with this AHJ, or other ones that he knows.
(Some AHJ's have good memories)

I'm not saying that AHJ's are vindictive if they "loose", but who knows.

The solution, in my humble opinion is to change the feeder. This way you can't really loose.

John

abode electric, In that case I would try to get the #12 passed, this keeps the GC happy.

If I could not, I would hope that I had some proof that the HVAC guy F***** up and I would back charge the repair or at least get something in return.

The inspector is sighting 240.4d without understanding that 20 amp on 12cu doesn't apply to airconditioning. Also it's a matter of principal. If you read it it's very clear, no gray area at all. It's right there in black and white.

abode electric...check out article 440-62/4
i think this applies to this.

440.62 is for window or wall AC, ones with cords

abode electric...this is not a wall or window unit. where is the ac unit.are we talking about an outside residential condensing unit.?

Hey if it`s an outdoor unit it should be apiece of cake to feed a #10 if needed.I would if it were me run the circuit and ask for the GC to foot the bill for the wire.If not you rest assured you have a better installation.I`ve personally done the exact same.I didn`t have 10 and ran 12 about a year later I was back running #10.A/c man insisted to the home owner 12 was to small and was the cause of the units problems.A while back I made a comment on a similar install about voltage drop on start up and the lights dimming and rescapt stated this was incorrect if you read this could you explain where it was the wrong conclusion.And the voltage drop wasn`t the cause of dimming lights,I did a search and didn`t find it..Thanks

Adobe, You must have amp'd the A/C unit to come up with the "about 17 amps". Then you say the name plate states 22amp min circuit ampacity. You have to use the name plate rating. So 22amps @ 125% is 27.5amps. You have to run #10. I got this from reading 440-2, " Branch-circuit selection Current" using the last sentence. The 22amps on the name plate does not take into account your 125%.

And to add fuel to the fire: Why is this not considered a continuous load? Some motels I've stayed at the A/C stayed on all the time.

Tom

Here we go again LOL!

Gisbon,

The 22 amp minimum circuit ampacity listed on the nameplate already has the 125% of compressor FLA and 100% of all other loads factored in. The manufacturer has already completed the calculation as per 440.32, it does not need to be repeated again in the field. Abode was just approximating the 17 amp FLA rating. 17.6 amps X 125% equals 22 amps.

If the nameplate states a minimum circuit ampacity of 22 amps, then thats what it is, 22 amps. Table 310.16 lists the ampacity of #12 wire at 25 amps in both the 60 and 75 degree columns. Article 240.4d does not limit the #12 wire to 20 amps for air conditioner loads as per 240.4g.

Yes, the NEC is a minimum standard, but minimum or not, #12 wire is legal for this air conditioner unless high ambient temperature and/or adjacent conductor factors apply. Although voltage drop compensation should be considered if it applies, it is not an NEC requirement, it is only a fine print note in article 210.19a.



[This message has been edited by Matt M (edited 01-29-2003).]