Condenser Question

[JohnDS]

1) I was told that when it comes to A/C condensers the 125% motor calculation does not apply. Instead you should just go by it's max ampere rating. So if it's 35a max load, you should size the circuit for 40a. If it's a 40amp max load, you should size the circuit for 40a also. Is this correct?
- if yes, is the continuous load calculation already taken into consideration with these numbers?


2) On the subject, i'm a little bit cloudy on the motor calculations in general. If you have an air compressor rated at 37a:

37a x 1.25 = 46.25a

So, size the circuit for 50a. Is this correct?

- and if it will be running for 3 hours or more what is the continuous load calculation and how does it apply in this example?


3)Is this the proper way to size circuits for all motors other than A/C condensers?
- what is the max allowable voltage drop on a motor circuit?

Thanks guys.

 

[infinity]

You are required to use the nameplate information if it's available. The MCA is used to size the conductors. The Maximum OCPD is used to size the breaker or fuse. The conductor size does not have to correspond to the breaker size.

For example an AC unit with an MCA of 24 amps and a MOCPD of 35 amps will allow #12 THHN conductors to be protected at 35 amps.

 

[electricman2]

For your compressor motor calculations, you will need to use the full load current listed in table 430.248 for single phase motors or 430.250 for 3 phase motors for the motor nameplate horsepower.

 

[teco]

Are you talking about an A-C compressor or an Air compressor? You mention both. For an A-C compressor check out 440.6 A and B.

Mark.

 

[R Bob]

You are required to use the nameplate information if it's available. The MCA is used to size the conductors. The Maximum OCPD is used to size the breaker or fuse. The conductor size does not have to correspond to the breaker size.

For example an AC unit with an MCA of 24 amps and a MOCPD of 35 amps will allow #12 THHN conductors to be protected at 35 amps.

Agreed.

In fact, if you take a look at the the other information on the name plate (comp FLA/LRA, fan FLA/LRA, etc.) and perform the NEC calculation you will probably find that the MCA comes out the same. The manufacturer has already computed the branch circuit calculation for us.