olly
Senior Member
- Location
- Berthoud, Colorado
- Occupation
- Master Electrician
I have an air conditioner, the name plate says max breaker size of 25A. I can get by with #12 CU since its a motor, is that right?
AC wire size
- Thread starter olly
- Start date
- Status
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
What is the MCA (minimum circuit ampacity) on the name plate, and what is the wiring method?
Cheers, Wayne
Cheers, Wayne
olly
Senior Member
- Location
- Berthoud, Colorado
- Occupation
- Master Electrician
Its 17A. THHN / THWN-2 in LFNC
- Location
- Connecticut
- Occupation
- Engineer
#14 would be acceptable, so #12 is fine.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Isn't most LFNC limited to 60C in wet areas, so that #12 would be required for the MCA of 17A?
Cheers, Wayne
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
This is an article 440 application, yes it has a motor, but the rules are a bit different.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I believe that you're correct.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I would like to see that section if anyone knows it. I don't see it in the 2017
- Location
- New Jersey
- Occupation
- Journeyman Electrician
It says it right on the side of the LFNC.
- Location
- Illinois
- Occupation
- retired electrician
356.12(2). There is similar language for all of the non-metallic raceways.
However you would base the conductor temperature on the actual operating load and not the MCA. With an MCA of 17, the actual operating load on a 14 AWG would be below its 60°C ampacity.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Doesn't MCA mean minimum circuit ampacity? The ampacity of #14 AWG in 60C rated LFNC is only 15A.
Cheers, Wayne
- Location
- Illinois
- Occupation
- retired electrician
Yes it does mean minimum circuit ampacity, but that is ~25% greater than the actual running current. The heat in the conductor is created by the actual running current and not by the inflated current required by the NEC and the product standards.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I have never noticed that
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I get what you are saying but if the unit says minimum cir. amp is 17 then I don't get why a conductor at 15 amps is allowed.
- Location
- Connecticut
- Occupation
- Engineer
The conductor doesn't have an ampacity of 15A. The section doesn't say the ampacity of the conductor must be based on the 60C column. It says the conditions of use can't exceed a 60C operating temperature.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Sorry, what distinction are you drawing here? Doesn't the 15A 60C ampacity of #14 Cu mean that for design purposes, #14 Cu carrying 15A continuously could reach 60C in temperature, assuming an ambient temperature of 30C and various other worst case conditions that go into the design numbers?
Cheers, Wayne
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I think they are saying the conduit used cannot be used in an area more than 60C. If the temp was more than 60C then you would have to use another raceway... I think
- Location
- Connecticut
- Occupation
- Engineer
As Don mentioned, It may not be carrying 15A continuously...it could be carrying less than 15A and therefore not reach 60C.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Sure, it may not be. But the A/C unit label calls for a conductor of a size that can carry 17A continuously. #14 Cu in LFNC can't do that without violating the 60C rating of the LFNC.
Cheers, Wayne
- Location
- Connecticut
- Occupation
- Engineer
The mca of the conductor has nothing to do with the operating temperature of the conduit. The actual load current and the ambient conditions affect the operating temperature of the conduit.
- Status