Sizing A/C disconnect

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klrogers

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NEC Code 2005:
I'm I correct in saying that with an a/c package unit with a MCA (minimum circuit amps) of 51 amps that a 60 amp unfused disconnect can be fitted, even if the branch circuit is from a 70 amp breaker?

440.12(B)(2) Disconnect shall be at least 115% of the sum of all currents at rated load

440.22(B)(1) referring back to 440.22(A) ...setting not exceeding 175%....


Kevin
 
Re: Sizing A/C disconnect

The 51 amps already contains the additional 25% so your 115% disconnect requirement is already met.
 
Re: Sizing A/C disconnect

Most nameplates also state a maximum amp rating as well. The AHJ's in my area always check for this.

I would reduce the overcurrent to 60 Amps. When I worked in Vegas, we would always pull larger sized wires to the AC's. We would then use fused disconnects to step it down to the correct size. The reason for this was that the AC's were always being replaced. The larger size wire was always large enough to carry the load.
 
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