Wire Sizing for Mini Split

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T74

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Friendly Debate over wire size for this unit.

#8 or #10?
 

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texie said:
Yes, and all breakers today are HACR rated per the standard. I'm thinking GoldDigger glossed over the HACR in the photo.
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How about because it says "Maximum FUSE" but does not specify Maximum Breaker?
The peripheral mention of HACR breaker does not change the actual language elsewhere on the label.
 
GoldDigger said:
How about because it says "Maximum FUSE" but does not specify Maximum Breaker?
The peripheral mention of HACR breaker does not change the actual language elsewhere on the label.
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I see what you are saying-there seems to be a conflict in the label. But it seems to me that the statement is pretty clear that it is approved for HACR breaker or fuse. One could always demand an answer from the NRTL about poor labeling language.
 
T74 said:
OK, How about #10 with a 30 amp breaker?
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You can do that but it may be a mistake with tripping issues down the road. 40 amp is perfectly compliant with #10 in this case- because the unit has overload protection which protects the conductors. The 40 amp is there just for ground faults and short circuits
 
Here are the code rules that allow this.
The basic rule is 240.4 protect a conductor at its ampacity 310.15, unless permitted or required in 240.4(A) thru (G)
(G) is overcurrent protection for specific conductor applications, it lists Art 440 Parts III, VI.

HVAC units are a bit different from motors as the windings are in the refrigerant. For motors we say "the overload protects the motor, the breaker protects the wire.
Don't get hung up on putting a 10 AWG on a 40 AMP breaker.
 
Buck Parrish said:
That 30 would never work properly. It would trip all the time. Most inspectors wouldn't pass it either
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Are you sure? The MCA already has a 125% factor added to it so the running current is probably less then 25 amps and an inverse time CB should allow the unit to start. Not saying I would do it but a 30 amp OCPD would be code compliant.
 
infinity said:
Are you sure? The MCA already has a 125% factor added to it so the running current is probably less then 25 amps and an inverse time CB should allow the unit to start. Not saying I would do it but a 30 amp OCPD would be code compliant.
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PHP:

Going by experience , even a 5 amp reduction will cause nuisance trips.
 
Buck Parrish said:
PHP:

Going by experience , even a 5 amp reduction will cause nuisance trips.
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There must be some distortion in the space time continuum centered over select cities where all this nuisance tripping happens. I actually cant recall seeing any nuisamce trips on transformers, motors. Or hvac units even when breakered at their mca or namplate (which I seem to see a lot as most non electricians don't know about the larger ocpd allowances for these devices). I had a 30 kva three phase 208-600 transformer (83 amps at 208) on a 60 amp breaker and it would trip on energizing about 1 out of 5 or 6 times.
 
Buck Parrish said:
PHP:


That 30 would never work properly. It would trip all the time. Most inspectors wouldn't pass it either
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I'm curious as to what NEC code you think would be cited to fail a 30 amp breaker installed on this particular unit. Continuous load is less than 24 amps.

To answer the OPs question, #10 is fine provided you aren't wiring this thing in a ridiculously hot ambient temperature and/or contending with a long run of wire.

And because it has not been mentioned, one could use a combination of fuses and Breakers as well, even mismatched ones like a 40 amp breaker and 35 amp fuses
 
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