NEC Motor conductor sizing
NEC Motor conductor sizing
(OP)
I have looked at previous threads on this subject and didn't find an answer to this. Or I missed it.
In a control panel we have a 3 HP 230/3/60 motor rated at 9.6 FLA. If we use NEC for Motor Circuit Conductors Sizing(Article 430-21.) For the conductor size we have FLA * 125 % or 12 amps or # 14 AWG.
The Circuit Breaker is 20 amps.
If we go to the wire capacity table in the appendix, we see # 14 THHN copper is good for 21 amps. But at the bottom of the table you have the:
"Unless otherwise specfically permitted elsewhere in this Code, the overcurrent protection for conductor types marked with an obelisk (which it is) shall not exceed 15 amperes for No.14, 20 amperes for No. 12 and 30 amperes for No. 10 copper".... and so on.
So do we use # 12 wire or is Article 430 the "Unless otherwise specfically permitted elsewhere in this Code" ?
Which size is correct??
Thanks!!
In a control panel we have a 3 HP 230/3/60 motor rated at 9.6 FLA. If we use NEC for Motor Circuit Conductors Sizing(Article 430-21.) For the conductor size we have FLA * 125 % or 12 amps or # 14 AWG.
The Circuit Breaker is 20 amps.
If we go to the wire capacity table in the appendix, we see # 14 THHN copper is good for 21 amps. But at the bottom of the table you have the:
"Unless otherwise specfically permitted elsewhere in this Code, the overcurrent protection for conductor types marked with an obelisk (which it is) shall not exceed 15 amperes for No.14, 20 amperes for No. 12 and 30 amperes for No. 10 copper".... and so on.
So do we use # 12 wire or is Article 430 the "Unless otherwise specfically permitted elsewhere in this Code" ?
Which size is correct??
Thanks!!





RE: NEC Motor conductor sizing
So in your case you can apply that exception and use 20A CB with #14 wire. If this were a lighting circuit, for example, the max. CB size permitted for #14 condutors would be 15A.
RE: NEC Motor conductor sizing
EC readers: #12 and #14 correspond to roughly 4 and 2.5 mm2, respectively.
Regards,
William
RE: NEC Motor conductor sizing
RE: NEC Motor conductor sizing
On the jobs I was referring to, the #12 minimum was a client's particular requirement for branch circuit wiring.
William
RE: NEC Motor conductor sizing
Mike McCowan
Automation Specialist
Industrial Automated Systems
mvmccowan@iasengineering.com