air conditioner question

howard.wheaton

I have (2) # 10 orange wires going to the central airconditioning unit from (2) 40amp breakers. First of all, these should be 30amps breakers correct due to the size of wires? And why is there 2? Doesn't there need to be a neutral?

HouseHelper

AC unit is 240 only, so no neutral is needed. Hermetically sealed compressors (AC) use a little different rules, so the 40A breaker on #10 wire is OK.

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micromind

As stated above, an A/C unit doesn't need a neutral, just the 2 hots.

The nameplate usually states a minimum circuit ampacity. This determines the wire size. It also states a maximum breaker or fuse size. The wire size is usually 'too small' for the breaker, but perfectly legal and safe.

The reason is because the A/C unit is self-protected against overloads, so it cannot overload the wire. It can however, develop a short-circuit. This is the sole function of the breaker; to protect against short-circuits and ground faults.

The reason the breaker needs to be larger than normal is because the compressor contains a motor. All motors draw much more current when starting than they do when running. (Usually about 6 times as much). A 'normal' size breaker might see this starting surge current as a fault and trip when there isn't a problem.

About the only places that a breaker can be larger than the wire is A/C units, motors, and welders. There are a few others, but you'll never find them in residential wiring.

Rob

JohnJ0906

Is this one or 2 units?

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