BREAKER of AC - Circuit Sizing. NEC 2014 440.4(B)

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You can use MCA and MOP for wire size and breaker size, respectively, and ignore the rest.

Simply put, you can use the smallest breaker you want that will allow the unit(s) to start reliably.
 
You're MCA is 132 amps which you can use to size the conductors, I would use #1/0. Your OCPD can be either 150 or 175 amps.
 
Julio Cesar said:
in the Video of Mike https://www.youtube.com/watch?v=OsTx38PVMTA&feature=share explain how to determinate the size of the conductor and the circuit breaker according to the NEC 2014.

I recently did and instalacion of some AC equipment. in the data plate have:

--------------------------------------------------------


MODEL: EBC300A3E0A00000000000000000000

COMPR#1 50.5 A (RLA)
COMPR#2 35.7 A (RLA)

FAN(S)
COND#1 4.6 A (FLA)
COND#2 4.6 A (FLA)
EVAP. STD 24.2 A (FLA)
EVAP. O/S 30.8 A (FLA)

-------------------------------------------------------------------

And.... I put a Breaker of 150A, when the max permitted by the data plate is 175A.

The question is:

1) Is correct to put a breaker less that indicate in te data plate? or always is necessary put the value indicate in the data plate?

I believe that this AC Unit will not have all the motors (6 motors) running all the time (150.4A) that's why I hope the breaker will function properly.



Thank you for your help.
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My answer is "maybe". You can down size a breaker as long as the equipment starts but, because this is a continious load you can't load a breaker to more than 80% of it's rating. If you have the standard size evaporator motor your at 119.2 amps full load (not mca) so you would be ok with a 150 amp breaker at 150 x .8=120 amps.

If you have the larger evap. motor your full load comes in at 126.2 and in that case a 150 amp breaker wouldn't work
 
Eddie702 said:
My answer is "maybe". You can down size a breaker as long as the equipment starts but, because this is a continious load you can't load a breaker to more than 80% of it's rating. If you have the standard size evaporator motor your at 119.2 amps full load (not mca) so you would be ok with a 150 amp breaker at 150 x .8=120 amps.

If you have the larger evap. motor your full load comes in at 126.2 and in that case a 150 amp breaker wouldn't work
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I would not consider this continuous load. The 150A breaker should be acceptable for either evaporator motor, as long as the equipment starts, as you have noted.
 
david luchini

Just a difference of opinion. Especially for a commercial job as far as I am concerned any HVAC equipment is a continuous load. If the HVAC unit is sized correctly it will run continuously on a design day.
 
Continuous, non-continuous, it does not matter according to the NEC when sizing the branch circuit. Just follow the nameplate and you're done. :)
 
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