mstrlucky74
Senior Member
- Location
- NJ
I copied the info below from some reading I was doing. so when sizing motor conductors you don't size off the ocpd at the panel unless the breaker amps are higher than the motor fla... if that's even allowed? how is the breaker sized for a motor?
Sizing branch-circuit conductors. Branch-circuit conductors that serve a single motor must have an ampacity of not less than 125% of the motor's FLC as listed in Tables 430.147 through 430.150 [430.6(A)]. You must select the conductor size from Table 310.16 according to the terminal temperature rating (60°C or 75°C) of the equipment [110.14(C)]. Let's reinforce this concept by working through a sample calculation. Refer to Fig. 4.
Example No. 3: What size THHN conductor do you need for a 2-hp, 230V, single-phase motor?
(a) 14 AWG
(c) 10 AWG
(b) 12 AWG
(d) 8 AWG
Let's walk through the solution:
Step 1: Conductor sized no less than 125% of motor FLC
Step 2: Table 430.148 shows the FLC of 2-hp, 230V, single-phase as 12A
Step 3: 12A × 1.25 = 15A
Step 4: Per Table 310.16, you need to use 14 AWG THHN rated 20A at 60°C
The minimum size conductor the NEC permits for building wiring is 14 AWG [310.5]. However, local codes and many industrial facilities have requirements that 12 AWG be used as the smallest branch-circuit wire. So in this example you might need to use 12 AWG instead of 14 AWG.
Sizing branch-circuit conductors. Branch-circuit conductors that serve a single motor must have an ampacity of not less than 125% of the motor's FLC as listed in Tables 430.147 through 430.150 [430.6(A)]. You must select the conductor size from Table 310.16 according to the terminal temperature rating (60°C or 75°C) of the equipment [110.14(C)]. Let's reinforce this concept by working through a sample calculation. Refer to Fig. 4.
Example No. 3: What size THHN conductor do you need for a 2-hp, 230V, single-phase motor?
(a) 14 AWG
(c) 10 AWG
(b) 12 AWG
(d) 8 AWG
Let's walk through the solution:
Step 1: Conductor sized no less than 125% of motor FLC
Step 2: Table 430.148 shows the FLC of 2-hp, 230V, single-phase as 12A
Step 3: 12A × 1.25 = 15A
Step 4: Per Table 310.16, you need to use 14 AWG THHN rated 20A at 60°C
The minimum size conductor the NEC permits for building wiring is 14 AWG [310.5]. However, local codes and many industrial facilities have requirements that 12 AWG be used as the smallest branch-circuit wire. So in this example you might need to use 12 AWG instead of 14 AWG.
