10-2 on 50 amp breaker

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Jim W in Tampa said:
A/C unit says min circuit amps 32 min. breaker 50 amps ,is this reall safe on #10 thhn ?
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Table 310.16 For #10 THHN 75d* is 35 amps. *240.4(D). #10-30 amps

If you use 10-2(Romex) then you would have to use the 60d rating of 30amps.

You stated 32 amp min. so as I see it you can not use 10-2.

I'm sure if I'm wrong someone will let me know.
 
1793 said:
Table 310.16 For #10 THHN 75d* is 35 amps. *240.4(D). #10-30 amps

If you use 10-2(Romex) then you would have to use the 60d rating of 30amps.

You stated 32 amp min. so as I see it you can not use 10-2.

I'm sure if I'm wrong someone will let me know.
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Is my thhn not ok to carry 35 amps ?My concern is the 50 amp breaker,really dont like it being that high.
 
Jim W in Tampa said:
Is my thhn not ok to carry 35 amps ?My concern is the 50 amp breaker,really dont like it being that high.
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I would tend to agree that if you used THHN then the 35 amps could be used, however I keep looking at the " * " that sends us back to 24.4(D) #10-30 amps.
 
1793 said:
I would tend to agree that if you used THHN then the 35 amps could be used, however I keep looking at the " * " that sends us back to 24.4(D) #10-30 amps.
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The "*" refers you to 240.4D which refers to 240.4E thru 240.4G. 240.4G
references table 240.4G. In this table section 440 allows the over current device to be 175% of the FLA of the A/C unit.
 
240.4(d) does not apply to AC units that fall under article 440. Your #10 THHN (75 degrees C=35 amps) may be used for this application however if you used NM cable than it's ampacity is limited to the 60 degree C column of 310.16 which is an ampacity of 30 amps. Therefore if using NM you would need #8-2 NM cable.
 
infinity said:
240.4(d) does not apply to AC units that fall under article 440. Your #10 THHN (75 degrees C=35 amps) may be used for this application however if you used NM cable than it's ampacity is limited to the 60 degree C column of 310.16 which is an ampacity of 30 amps. Therefore if using NM you would need #8-2 NM cable.
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Thanks for helping and the clarification.
 
I thought this would be easy, but I'm not sure. 240.4(D) says #10 can only be used with breakers up to 30A unless "specifically" permitted in 240.4E or G. Although 240.4(G) refers to article 440, I don't see anything in 440 that "specifically" says #10 can be used at 50A.

My guess is that #8 is required.

Steve
 
bob said:
The "*" refers you to 240.4D which refers to 240.4E thru 240.4G. 240.4G
references table 240.4G. In this table section 440 allows the over current device to be 175% of the FLA of the A/C unit.
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I agree that the over current can be larger. I was referring to the ampacity used for the #10 THHN or #10-nm which I still think 240.4(D) states #10-30amps. The OP states min ampacity of 32 amps.
 
steve66 said:
I thought this would be easy, but I'm not sure. 240.4(D) says #10 can only be used with breakers up to 30A unless "specifically" permitted in 240.4E or G. Although 240.4(G) refers to article 440, I don't see anything in 440 that "specifically" says #10 can be used at 50A.

My guess is that #8 is required.

Steve
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I would disagree. What is the ampacity of #10 THHN?

Answer is 40 amps.

For other then derating can we use the 40 amp rating?

No, because we know that the terminations that we use are rated for 60 or 75 degrees, so the ampacity is limited to either the 60 or 75 degree rating.

Furthermore 240.4(d) reduces the ampacity to 30 amps unless it is used for equipment covered under Article 440. Since an AC unit is covered under article 440, 240.4(d) does not apply.
 
steve66 said:
I thought this would be easy, but I'm not sure. 240.4(D) says #10 can only be used with breakers up to 30A unless "specifically" permitted in 240.4E or G. Although 240.4(G) refers to article 440, I don't see anything in 440 that "specifically" says #10 can be used at 50A.

My guess is that #8 is required.

Steve
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440.22(A) ...over current can not exceed 175%... this is for the inrush of current at start up.

We can size for min. and protect for max.
 
infinity said:
I would disagree. What is the ampacity of #10 THHN?

Answer is 40 amps.

For other then derating can we use the 40 amp rating?

No, because we know that the terminations that we use are rated for 60 or 75 degrees, so the ampacity is limited to either the 60 or 75 degree rating.

Furthermore 240.4(d) reduces the ampacity to 30 amps unless it is used for equipment covered under Article 440. Since an AC unit is covered under article 440, 240.4(d) does not apply.
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So are you saying that we can load the #10 to the 35 amps(310.16 75d)
 
1793 said:
So are you saying that we can load the #10 to the 35 amps(310.16 75d)
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Yes, the 75 degree ampacity may be used for equipment that is listed in Article 240.4(G). However if NM cable is used, 334.80 would limit the ampacity to the 60 degree column. For the AC unit in the OP the MCA is 32 amps. The conductor is sized according to the MCA. The OCPD is sized according the the maximum listed on the unit. This is permitted since the OCPD is only providing short circuit and ground fault protection.
 
Usually i dont end up in this tight of a jam.We provided what the print called for but as always noone knows what unit will arrive untill trimout.I was pretty sure i was ok but like others bit reluctant to fuse at 50
 
Do you know the temperature rating of all the terminations?If not, you must use the 60 degree column since it is under 100A and smaller than 1/0 according to 110.13C. Or am I missing something in 440 that overrides this general rule?
 
Jim W in Tampa said:
You have a good point.I am assuming my CH breaker and pullout disc.are 75
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Jim I will be surprised if the CH breaker is not rated 75 C.

The pull out on the other hand......

I remember Websparky mentioned he finds the inexpensive HVAC pull outs only rated 60 C during his inspection duties.

You may want to take a look see. :)
 
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