air unit disconnect

kbc1

when wiring a unit with a 30 amp disconnect do you need 10/2 or 10/3 ,please explain, code ref if possible

darren

Depends if the unit is 240 or 240/120V. If it is 240V you need 10/2 if it is 240/120V you would need 10/3.

The 3rd wire is your neutral and is needed to get 120V.

kbc1

how would u know what it is

k_buz

I don't agree with this answer. The wiring isn't dependent on the disconnect. The wire size is dependent on what the AC unit calls for. Many units today only require a 20A 240V circuit. In this case, you would run 12/2.

If the unit says something like Min Circuit Ampacity = anything under 20A there is a good chance you can run 14's even.

This answer is only accurate for the NEC. If you can post a picture of the information provided on the plate, we can tell you for sure.

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darren

How can you disagree with me when I said the same thing, I never mentioned anything about the disconnect in my answer.

To the OP look at the name plate for 3 important numbers
Voltage(most likely 240V)
MCA(minimum circuit capacity-you can size your wire to this)
MOPD(maximum over current protection device-size your breaker to this)

k_buz

No you didn't, but the OP asked what size wire would be used to wire a 30A disco for an AC unit. You said you'd use 10/2 or 10/3. I wouldn't necessarily do it that way. I'd use the size wire the AC required. That's all. Just giving the OP the possibility to use a smaller cheaper wire.

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jbfan

The op stated 10/2 or 10/3.

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k_buz

Good point, I guess I just expanded because we don't really size wires to appliance disconnects, we size the wire to the appliance. I took the OP's question as he was using #10's because it was a 30A disco.

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darren

True but I assumed he had 10/2 and a 30A disconnect he needed a 30A circuit.

electures

Unless the disco is fused. #10's to a fuse disco can't exceed a 30A breaker.

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All responses based on the 2011 NEC.
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