Supplying elec for HVAC unit in a small house


Old 06-18-13, 09:55 PM
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Question Supplying elec for HVAC unit in a small house

I'm redoing some electrical work in an old house. Its an old 2 bedroom, 2 bathroom house that has a standard size HVAC unit. Just checking to see if the wires and circuit breaker that was run is adequate.

What size electrical wire should be supplying the HVAC unit? 12-2 or 12-3? Or something else? What about the circuit breaker? Is a 20-amp breaker OK?
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Old 06-18-13, 10:02 PM
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If its 240 two conductor cable, X-2, where X is determined by the FLA. 12-2 would be correct for a 20 amp breaker unless manufacturers recommendations are different. AC compressors are different than normal wire sizing. The wire is determined by full load amps and the breaker by starting current.

Last edited by ray2047; 06-19-13 at 06:05 AM. Reason: Clarification.
Old 06-18-13, 10:37 PM
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The breaker requirement should be on the outdoor unit's nameplate (near where the refrigerant lines connect). Normally there will be a minimum and maximum amp rating listed. The maximum breaker ampacity dictates the breaker size, and the minimum circuit ampacity size dictates the wire gauge.

Last edited by pcboss; 06-19-13 at 06:28 AM. Reason: clarification
Old 06-19-13, 04:25 AM
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The nameplate listing the minimum circuit ampacity and the max fuse breaker is just that.

For example, a unit that has MCA-15, max fuse or HACR breaker-35, means you need to have a circuit minimum of 15 amps (14 gauge) and you can put it on a breaker or fuse up to 35 amps.

So, in this instance, you can have 14 gauge wire on a 35 amp breaker due to the rules that apply in articles 430 and 440.
Old 06-19-13, 06:30 AM
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If the unit says Max Fuse size, you will need to have fuses in the disconnect. Otherwise a HACR rated breaker is fine.

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