Min. Cir Ampacity 30.9

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Dennis Alwon

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Chapel Hill, NC
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but I thought he could only use this wire for the given application (article 440) under 2 conditions:
1) 60 degree column works (it doesn't, he needs next size #8)
2) per 440 (or 430 per 440.7), the unit is marked and says on the label "max size breaker 50A" (he didn't say this but I am guessing everyone assumed it ?)

I am not sure what you are asking. What is "this wire" I put it in bold in your response.
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
Unless you want to change to some other wiring method than NM.
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
You're right on the 75? as long as the termination are rated at 75? (most are), and your THHN would be fine for this INSIDE unit, but not an outside condensing unit.
 

One-eyed Jack

Senior Member
With all the talk about the 60 degree coloum in 310.16. I am second guessing my self. Is #10 Romex okay on a 240 v Geothermal Heat Pump? The breaker will be 50 amps, the minimum circuit ampacity is 30.9.
Is romex #10-2 WG okay?

The min cir ampacity means just that . Ref. 240.4 D (7) The max overcurrent protection is 30. This would be a code violation on wire size and ocp. The mfg. calculation 30.9 for min cir ampacity takes precedence over all other calculations. #8 would be required regardless of wire type. Then you could use the 50 amp ocp based on mfg. calculations.
 
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