AC unit

[woodsremodel]

I am wiring in an AC unit and just wanted some opinions on breaker size and disconnnect size. The min circuit ampacity is 33. The max over current protection amps is 50.
Thank You!

 

[JFletcher]

Welcome. The maximum circuit breaker size (MOCP) is 50A. As your MCA is 33A, you will need #8 wire or larger. A standard AC disco is good for 60A.

 

[woodsremodel]

So I should use a 60amp disconnect even though the max is 50? As long as I stick with a 50a breaker.

 

[JFletcher]

So I should use a 60amp disconnect even though the max is 50? As long as I stick with a 50a breaker.

The maximum breaker (or fuse) size is 50A. The disconnect is not a breaker, really just a big switch, tho they do make fused disconnects and ones with breakers in them.

Here, I'd use a GE or Midwest 60A non-fused exterior disconnect, costs about $8 from HD:

http://www.homedepot.com/p/GE-60-Amp-240-Volt-Non-Fuse-Metallic-AC-Disconnect-TFN60RCP/100674085


Yes, the disconnect rating has to be at least the size of the breaker. A 60A disconnect is good for up to 60A.

 

[petersonra]

Yes, the disconnect rating has to be at least the size of the breaker.

is that actually true? I thought it had to do with the load and not the OCPD rating.

 

[infinity]

is that actually true? I thought it had to do with the load and not the OCPD rating.

115% comes to mind.

Also the OP could use #10 MC cable or #10 AWG 75° C conductors in a raceway which has an ampacity of 35 amps. For NM cable your stuck with the 60° C ampacity so you would need a minimum of #8 as JF has stated.

 

[mbrooke]

I have the same question (curiosity) regarding this. If the wire can be smaller than the breaker, why not the disco?

 

[JFletcher]

is that actually true? I thought it had to do with the load and not the OCPD rating.

You and infinity are correct:

http://www.electricianmath.com/neccalculations/motordisconnect.htm

In this case, a 60A disco would be larger than needed. I do not think anyone makes a 40A (33x.1.15 = 37.95A) or 50A disco; maybe a 40A rated switch?

MCA already has the 115% figured doesnt it?

Infinity is also correct in that #10 is fine if not using NM/UF, which I assumed the OP would be using, up to the disco anyway.

 

[kwired]

440.12 covers the disconnecting means. There is quite a bit in there so I won't quote it.

The already mentioned 115% seems to be key, but is 115% of RLA of the compressor but if there are other loads besides just the compressor it does increase.