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Old 11-07-2012, 05:09 PM   #1
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when wiring a unit with a 30 amp disconnect do you need 10/2 or 10/3 ,please explain, code ref if possible

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Old 11-07-2012, 05:26 PM   #2
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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.

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Old 11-07-2012, 05:41 PM   #3
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how would u know what it is
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Old 11-07-2012, 05:51 PM   #4
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Originally Posted by darren View Post
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.
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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Old 11-07-2012, 10:05 PM   #5
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Originally Posted by k_buz View Post
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.

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)

Last edited by darren; 11-07-2012 at 10:08 PM.
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Old 11-07-2012, 10:16 PM   #6
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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)

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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Old 11-07-2012, 10:17 PM   #7
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The op stated 10/2 or 10/3.
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Old 11-07-2012, 10:23 PM   #8
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The op stated 10/2 or 10/3.
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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Old 11-07-2012, 11:43 PM   #9
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Originally Posted by k_buz View Post
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.
True but I assumed he had 10/2 and a 30A disconnect he needed a 30A circuit.
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Old 11-26-2012, 09:50 PM   #10
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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.
Unless the disco is fused. #10's to a fuse disco can't exceed a 30A breaker.

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