A/C 40 Min / 40 MAX

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1793

Senior Member
Location
Louisville, Kentucky
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Inspector
I have a customer with an A/C unit with a nameplate that states running ampacity is 24.5A and the Min & Max OCP both say 40A. So can this be wired with #10-NM?

I know we wire for lower and protect for Max, but what to do when Nameplate Min & Max are the same? :?
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
I would do 12AWG and 40A OCPD. Assuming voltage drop will not be an issue.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
This project involves removing the existing NM wiring due to damage. I'm planning on using NM again so I'm going to go with #10.

That would be the minimum if using NM cable. MC cable will get you 25 amps using #12.
 

JDB3

Senior Member
}}That would be the minimum if using NM cable. MC cable will get you 25 amps using #12. {{{

Not doubting you, just, what type of insulation is on the MC cable, if #12 will get you 25 amps?
Most of my stuff is residential, so just wondering.
 

rhovee

Member
A majority of the time you need to follow 240.4 (D) 1-7. This is where you get the #14 is good for 15 amps and #12 is good for 20 amps.... Also if you are a resi/romex guy then you are familiar with 334.80 which states that NM cable ampacity is determined on the 60 degree column. If you go back to article 240.4 (G) it will give you a table that gives exceptions to (#12 is good for 20 amps rule). Air conditioners and motors are listed in this table. That is why you could use 12-2 MC for 25 amps. The insulation would be THHN/THWN. The terminations would limit you to using the 75 degree column. Hope this helps.
 

ActionDave

Chief Moderator
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Location
Durango, CO, 10 h 20 min from the winged horses.
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}}That would be the minimum if using NM cable. MC cable will get you 25 amps using #12. {{{

Not doubting you, just, what type of insulation is on the MC cable, if #12 will get you 25 amps?
Most of my stuff is residential, so just wondering.
With NM cable you are required to use the sixty degree column 334.80, MC you are not.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
A majority of the time you need to follow 240.4 (D) 1-7. This is where you get the #14 is good for 15 amps and #12 is good for 20 amps.... Also if you are a resi/romex guy then you are familiar with 334.80 which states that NM cable ampacity is determined on the 60 degree column. If you go back to article 240.4 (G) it will give you a table that gives exceptions to (#12 is good for 20 amps rule). Air conditioners and motors are listed in this table. That is why you could use 12-2 MC for 25 amps. The insulation would be THHN/THWN. The terminations would limit you to using the 75 degree column. Hope this helps.


Never understood those restrictions, but you are correct. MC can go over the 60 degree column, and with motors the blanket limitations are lifted. 90* is still derating no matter what.v
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
If NM or MC i'd go with #10. I would not want the A/C guy complaining to me if the unit has starting issues.
 
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