Air condenser

[kevin1564]

I usually use the max breaker size and size the wire based on that. The customer Has a 45 amp breaker with 10 awg wire. It’s hard to read but it looks like the minimum ampacity and fla of the equipment contradict each other. Would the minimum circuit ampacity supersede the fla based on the unit isn’t running at full capacity? If so would it just be a breaker change for the 10 awg wire?

 

[winnie]

See https://www.manualslib.com/manual/705675/Amana-Rce-Prestige.html?page=4#manual

It looks to me like the label formatting in your picture makes things confusing. The label says 19.87 FLA 137 LRA which sort of makes it look like the motor full load amps rating is 137 (or 37). But the compressor motor 'Full Load Amps' is 19.87.

In any case the requirement is a minimum circuit ampacity of 26.54A, which the 10 AWG wire meets, and Max OCPD of 45, which the 45A breaker meets.

-Jon

 

[d0nut]

I may be misreading the label since it is so faded, but it looks like a MCA of 26.54A and an MOCP of 45A. It also looks like the FLA of the compressor is 19.87A and the fan is 1.5A. If those values are correct, the existing installation appears correct.

Edit: I was too slow typing. Now we have an echo.

 

[kevin1564]

if the breaker is 45 amp and the wire is rated for 35 wouldn’t we want to change the breaker to match the wire size. Or is there something about air condensers that I’m missing?

 

[LarryFine]

if the breaker is 45 amp and the wire is rated for 35 wouldn’t we want to change the breaker to match the wire size.

No. The A/C contains its own overload protection, so the breaker only needs to provide sort-circuit protection.

Or is there something about air condensers that I’m missing?

Yes. See 240.4.

 

[kwired]

View attachment 2559868I usually use the max breaker size and size the wire based on that. The customer Has a 45 amp breaker with 10 awg wire. It’s hard to read but it looks like the minimum ampacity and fla of the equipment contradict each other. Would the minimum circuit ampacity supersede the fla based on the unit isn’t running at full capacity? If so would it just be a breaker change for the 10 awg wire?

MCA is the result of 1.25 x compressor rated amps plus the condenser fan motor. I come up with figure very close to what it has, might be there is one more digit on the fan motor that isn't readable anymore that is throwing my result off just a little.

As far as the 10 AWG wire goes on the 45 amp breaker that is acceptable in this situation. The general rules of 240 don't apply, table 240.3 sends you to art 440 for overcurrent protection rules here.

With both art 430 and 440 applications you get higher OCPD for the branch circuit device than for other general applications in 240. They need this high short circuit/ground fault trip level to be able to hold during starting. The normally required separate motor overload protection device protects the motor as well as the conductor from overloads.

**Larry posted while I was composing this.

 

[augie47]

You might review this recent thread:

HVAC - HCAR Breakers vs conductor size being protected

I take this to the forum because I have seen a lot of confusion on this subject. I am under the impression the HCAR breaker size is to protect the conductor according to Table 310.15. This was the info sent to me which I believe is an opinion. Can the forum help to solve this confusion. Thanks...

forums.mikeholt.com

 

[kevin1564]

Thanks guys I appreciate the feedback. I always knew that instantaneous trip breakers were sized based on the LRC with overload relays at the equipment. I did not realize inverse time breakers were to be sized based on LRC in some cases. It all makes sense now. Thanks!

 

[kwired]

Thanks guys I appreciate the feedback. I always knew that instantaneous trip breakers were sized based on the LRC with overload relays at the equipment. I did not realize inverse time breakers were to be sized based on LRC in some cases. It all makes sense now. Thanks!

Not really based on LRC but rather some multiple of the rated or full load current. NEC maximums are 2.5 times for inverse time and 8 times for instantaneous trip with regular induction motors. There is provisions to increase that if it won't allow the motor to start. Many manufacturer tables and charts can be less than the 250% the NEC allows as their recommendation.

A 10hp 480 volt 3 phase motor has NEC FLA of 14 amps. NEC permits it to be on up to 35 amp T-M breaker, many manufacturer tables recommend a 25 amp breaker, I've seen many of them that are not driving something with high torque demand at startup hold on a 15 amp breaker.