Residential outdoor AC/Heat pump

[Matt Mckenzie]

NEC states that the conductors supplying outdoor residential AC/Heat pump must be calculated at 125% of the nameplate MCA on the outdoor equipment. The manufacturer of the outdoor equipment states that the calculation to get the MCA already includes the 125% of the FLA. Is there anyway in the NEC that we can prove to the local inspector that we really don't have to size the conductor another 125% of the MCA on the nameplate?

 

[Johnhall30]

You do not have to size the conductors at 125% of the MCA. You can go up to the next wire above the MCA and use that conductor.

 

[Dennis Alwon]

NEC states that the conductors supplying outdoor residential AC/Heat pump must be calculated at 125% of the nameplate MCA on the outdoor equipment. The manufacturer of the outdoor equipment states that the calculation to get the MCA already includes the 125% of the FLA. Is there anyway in the NEC that we can prove to the local inspector that we really don't have to size the conductor another 125% of the MCA on the nameplate?

There should be the actual current shown on the nameplate then multiply by 125% you should get the mca.

 

[Buck Parrish]

NEC states that the conductors supplying outdoor residential AC/Heat pump must be calculated at 125% of the nameplate MCA on the outdoor equipment. The manufacturer of the outdoor equipment states that the calculation to get the MCA already includes the 125% of the FLA. Is there anyway in the NEC that we can prove to the local inspector that we really don't have to size the conductor another 125% of the MCA on the nameplate?

You would need all the context to see that the NEC states that the nameplate shall be used. The manufacturer has already figured it in to the name plate rating.

Try showing the inspector 440.6(A) and (B)

 

[kwired]

You would need all the context to see that the NEC states that the nameplate shall be used. The manufacturer has already figured it in to the name plate rating.

Try showing the inspector 440.6(A) and (B)

Maybe 440.4 (A) and (B) as well. MCA is referenced there though it sends you to part IV to tell you how that MCA is determined even though manufacturer is the one that calculates it and marks it on the nameplate.

 

[infinity]

NEC states that the conductors supplying outdoor residential AC/Heat pump must be calculated at 125% of the nameplate MCA on the outdoor equipment.

Does it really say that?

The MCA is the minimum conductor size, it says it right in the acronym. Not sure what else an inspector should need. Use that number to size the conductors and send the inspector for some additional training.

 

[Tulsa Electrician]

Send him this link sounds like he needs a good read.

Air-Conditioning Equipment Installations

iaeimagazine.org

 

[Buck Parrish]

Does it really say that?

The MCA is the minimum conductor size, it says it right in the acronym. Not sure what else an inspector should need. Use that number to size the conductors and send the inspector for some additional training.

I agree with y'all . I was quoting the OP's post. That's why I said he would need all the context. Sounds like he may have found something over in 430 that had the inspector confused.
IMO It's elementary to not know how to size a wire or a breaker for a condenser. But I can see a lot of inspectors not knowing how.

 

[mtnelect]

All the installing Electrical Contractor has to do, is refer to the manufacturer installation manual for proper wiring information. See attached example:

 

[kwired]

All the installing Electrical Contractor has to do, is refer to the manufacturer installation manual for proper wiring information. See attached example:

That just mentions MCA of different units in that series of product that should also be on nameplate of each individual unit, it doesn't tell you anything about what MCA actually is/means.

 

[mtnelect]

Attached is the full Installation Manual with more details. The manufacturer has already taken into consideration the refrigerant cooling effect on the compressor when listing the electrical requirements.

 

[mtnelect]

Attached is the full Installation Manual with more details. The manufacturer has already taken into consideration the refrigerant cooling effect on the compressor when listing the electrical requirements.

The hermetically sealed compressor is not like a standard motor, the return (suction) refrigerant passes over the motor windings and reduces the required energy. That is why there is Section 440.4(A)

 

[kwired]

The hermetically sealed compressor is not like a standard motor, the return (suction) refrigerant passes over the motor windings and reduces the required energy. That is why there is Section 440.4(A)

that very well may be a factor in the existence of 440.4(A).

There are other non standard motors out there that similar circumstances can happen, like air over rated motors, fan cooled motors that the fan is not driven by the same shaft as motor being cooled or even possibly something liquid cooled.