Hvac wire sizing

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Toddyh

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I received incorrect information from the HVAC contractor on a job. I was told the unit was going to be a 3 ton and they install a 5 ton. I ran #10 to Romax to the unit. It seems like I can get away with this but I'm not sure. Doing research online I keep contradicting what I find.
Min circuit amp 35
Min Brk 45
Max brk 60
Rla 26.4
Fan fla 1.2

Normally I would run a number 8 to this. But I think #10 will
Be ok for code since it's rated at 35.

What do you think?
 
Welcome (again!). You created an account 8 years ago and are now posting for the 1st time? :jawdrop:

Dennis summed it up. #10 NM is only good for 30A OCPD. #8 or #6, if a long run, is what you will need, especially if any part of the unit is outdoors.
 
If the MCA of the condenser is 30A and maximum OCPD is 45A then the OP is ok to use NM cable of 10awg.
 
With an MCA of 35 amps you could us #10 MC cable as long as your terminations are rated for 75° C. Same for conductors in a raceway.
 
Toddyh said:
Thanks for the replies. I'm kind of nervous leaving the 10 romex I think I will change it.
Click to expand...

If MCA is 35 then as stated earlier you have to change the 10 to a larger gauge.

However, if the MCA is 30 or less then I THINK you can leave the 10 and install a MAX breaker and you are still OK.

If I am wrong I am sure others will set me straight.
 
Toddyh said:
I found this video of Mike holt and this would make me think I'm ok with 10.https://m.youtube.com/watch?v=9lPDYEAgWD4
Click to expand...
Look at that video closely... He was dealing with a nameplate value of 30.1 amps which he downsized to 30.0.
You are dealing with a nameplate with 35 amp MCA. As Dennis pointed out way back in Post #2, IF you are dealing with NM (Romex), Art 334 restricts the ampacity to the 60° rating which is 30 amps and not adequate for your 35 amp load.
 
edward said:
If the MCA of the condenser is 30A and maximum OCPD is 45A then the OP is ok to use NM cable of 10awg.
Click to expand...
With a number of other wiring methods that would be correct, but it is not correct for NM. NM is restricted to the 60°C ampacity by the rule in 334.80.
 
MCA 30 amps and UF cable

MCA 30 amps and UF cable

If I have a HVAC unit that states MCA as 30 amps. What is smallest UF cable that can be used?
 
don_resqcapt19 said:

With a number of other wiring methods that would be correct, but it is not correct for NM. NM is restricted to the 60°C ampacity by the rule in 334.80.
Click to expand...

I agree that 334.80 limits the ampacity to the 60degree column of 310.15(B)(16) at 30A.

Back to my example, if the MCA of the HVAC equipment is 30A but the maximum OCPD is 45A then in this example a 10 awg NM cable will be code compliant with a 45A OCPD.
 
edward said:
I agree that 334.80 limits the ampacity to the 60degree column of 310.15(B)(16) at 30A.

Back to my example, if the MCA of the HVAC equipment is 30A but the maximum OCPD is 45A then in this example a 10 awg NM cable will be code compliant with a 45A OCPD.
Click to expand...
I did not notice that you changed the MCA...the OP has an MCA of 35A
 
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