40A Circuit Through Attic
- Thread starter PWR73
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I don't think A/C units are typically considered continuous loads by defintion, but the circuit must be sized to the MCA which is not less than 125% of the rated -load current (440.32) so it is the same
The circuit ampacity would normally be determined by the MCA listed on the nameplate.
If a load is 40 amps and is continuous then you would need a conductor rated at 50 amps, or a #6 NM.
There is no problem in your installing a #6, but I think most inspectors would look at the A/C unit MCA and assure the cable installed was adequate for that number.
The circuit ampacity would normally be determined by the MCA listed on the nameplate.
If a load is 40 amps and is continuous then you would need a conductor rated at 50 amps, or a #6 NM.
There is no problem in your installing a #6, but I think most inspectors would look at the A/C unit MCA and assure the cable installed was adequate for that number.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
60/2 must be one very small cable . :grin:
Perhaps it was the ambient temp or you added 125% to the a/c unit where the mca already has 125% added to it.
Perhaps it was the ambient temp or you added 125% to the a/c unit where the mca already has 125% added to it.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
There very well may be a problem with 250.122(B)
Volta
Senior Member
- Location
- Columbus, Ohio
Good point.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
"As Nanna Roseannadanna used to say, 'It's always something!'"
But if he ran 6-2 nm cable, whats the problem?
- Occupation
- Licensed Electrician
250.122(B) says that any time you oversize your conductors your EGC has to be increased in size proportionally. 6-2 would only have a #10 EGC.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
the only things I can think of is the high ambient temps in the attic, voltage drop, and the best reason: it is what you had on the truck:grin:
Volta
Senior Member
- Location
- Columbus, Ohio
Exactly. If the circuit could have been installed with #8, then we effectively increased the size, so using circular mils, #6/#8 = 1.59 times bigger than needed. So the EGC would also need to be 1.59 times bigger than the #10 we could have used, so 10380 cmils x 1.59 = 16504, so a #8 Equipment Grounding Conductor would be required.
Or, raise the temperature of the attic until a #8 wouldn't be big enough.
Or, increase the size of the OCPD and/or load until a #8 wouldn't be big enough.
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