430.52 Motor overcurrent protection

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Greg1707

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I this sized correctly?

Motor 240 volts 2 horsepower.

Minimum Circuit Ampacity 13.4 amps x1.25= 16.75 #12NM
Overcurrent protection 13.4 amps x 2.5= 33.5 40 amp breaker.
 
Circuit ampacity is from the tables. It’s a conservative value so if a motor is replaced the BC wires will be large enough.
 
70% efficiency and .69 power factor. You will need to use the actual FLA in this case, not the table value. But as mentioned, a 35 A breaker, I think.
 
David Castor said:
70% efficiency and .69 power factor. You will need to use the actual FLA in this case, not the table value. But as mentioned, a 35 A breaker, I think.
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Actually that is the exception in 430.6 but I don't see this as an appliance. My comment above was more a surprise that the Table was lower than the nameplate. I was under the assumption that the Table was always higher than the nameplate.

Exception No. 3:
For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, the motor full-load current marked on the nameplate of the appliance shall be used instead of the horsepower rating on the appliance nameplate to determine the ampacity or rating of the disconnecting means, the branch-circuit conductors, the controller, the branch-circuit short-circuit and ground-fault protection, and any separate overload protection.
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Do you think the NEC covers all possible situations? You would actually size a motor feeder based on the NEC table if the nameplate FLA is higher?


See 430.6 A 1
 
David Castor said:
Do you think the NEC covers all possible situations? You would actually size a motor feeder based on the NEC table if the nameplate FLA is higher?


See 430.6 A 1
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Agree. The normal way of sizing the conductors is by using the table. But, considering the nameplate amperage is higher than that of the table, the correct sizing should be based on the higher amps! As one is required to set the thermal overload based on the nameplate amps, it is but logical to adjust the conductor size as the protection setting should be lower than the conductor capacity (otherwise, your conductor gets toasted before the TOL trips!.
 
I note that this name plate indicates "chore motor" which I think is a high torque motor. AFAIK the NEC does not recognize this. Interesting question. I don't recall the code saying use Table values unless the nameplate is higher.
 
A "chore motor" is described as an extra high torque motor and 430.6 would use the nameplate amperage in this situation.

. Motors built for low speeds (less than 1200 RPM) or high torques may have higher full-load currents, and multi‐ speed motors will have full-load current varying with speed, in which case the nameplate current ratings shall be used

but, as David noted, the next size up breaker would be a 35 amp
 
I looked up chore motor, its a high torque motor, which is not in my wheelhouse. All my experience has been with Class Bs.
I did note this motor is thermally protected, which does simplify the application.
 
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