AC wire size

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Stevenfyeager

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United States, Indiana
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electrical contractor
My HVAC man says the outside AC 5 ton unit requires 36 amp circuit capacity and 60 amp Max breaker. I use 8 -2 Copper on a 60 amp circuit breaker, right? I know we don't size AC wire the same as we do other loads. Thanks
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
My HVAC man says the outside AC 5 ton unit requires 36 amp circuit capacity and 60 amp Max breaker. I use 8 -2 Copper on a 60 amp circuit breaker, right? I know we don't size AC wire the same as we do other loads. Thanks
You can size the wire by the MCA not the breaker size. The reason is that the motor overload provides the wire protection against small overloads while the breaker at Max OCPD will provide short circuit and ground fault protection good enough for the smaller wire.
So do the ampacity calculation based on 36A. And use the 60A breaker to minimize the chance of starting trips.
 

infinity

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New Jersey
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Journeyman Electrician
My HVAC man says the outside AC 5 ton unit requires 36 amp circuit capacity and 60 amp Max breaker. I use 8 -2 Copper on a 60 amp circuit breaker, right? I know we don't size AC wire the same as we do other loads. Thanks

Yes, according to the data that you've provided #8 AWG (40 amp conductor) and a 60 amp OCPD would be code compliant.
 

kwired

Electron manager
Location
NE Nebraska
My HVAC man says the outside AC 5 ton unit requires 36 amp circuit capacity and 60 amp Max breaker. I use 8 -2 Copper on a 60 amp circuit breaker, right? I know we don't size AC wire the same as we do other loads. Thanks
It is not just AC units, it is anything with a motor that has similar rules. Motors draw heavy current at start up, and require higher breaker/fuse setting to be able to start, but this is for such a short duration that it doesn't overheat the conductors which are sized to the full load rating. The conductors are still protected from overloading by the motor overload protection device.
 

Stevenfyeager

Senior Member
Location
United States, Indiana
Occupation
electrical contractor
It is not just AC units, it is anything with a motor that has similar rules. Motors draw heavy current at start up, and require higher breaker/fuse setting to be able to start, but this is for such a short duration that it doesn't overheat the conductors which are sized to the full load rating. The conductors are still protected from overloading by the motor overload protection device.
Thank you
 
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