Motor Conductors

[volt101]

When selecting the ampacity of conductors fora single motor, the rules set in 430.22 apply. If after you multiply thefull-load current in the motor tables and the product comes out to a value thathas an asterisk next to the conductor?s size in Table 310.16 [Double asteriskin the 2011?s Table 310.15(B)(16)], does the small conductor rules apply? Example:Assuming all terminations are rated for 75?C - Can a 115-volt single phase ?horsepower motor be wired with 14 AWG, or does it need to have 12 AWGconductors to be code compliant?

 

[don_resqcapt19]

The "small conductor" rules do not apply to motor conductors. See 240.4(G).

 

[volt101]

That is just it. That exempts 430. Just not part II. That is where conductor sizing is.

 

[renosteinke]

Follow that asterisk!

It's more accurate to consider our common 'rule of thumb' wire sizes as the exception .... after all, there are at least ten situations specified where the 'rule' does not apply.

 

[Jim Shorts]

You are dealing with 2 separate issues. Overcurrent protection is addressed by the asterisk and is covered by Article 240. Conductor ampacity is addressed in Table 310.16 or Table 310.15(B)(16) in the 2011. 430.22 requires the conductor to have an ampacity at least 125% of the full load current as found in the motor tables. That is found strictly based on the ampacity table in article 310. Overcurrent protection (or branch-circuit, short-circuit, and ground-fault protection) is address in 430.52 and the rules found in article 240 are excluded by this section and in 240.4(G). In other words the rule for small conductors in 240.4(D) does not apply to motors. 14 AWG copper THW conductors are suitable for use as branch circuit conductors to supply a 3/4 hp, single phase, 115 volt motor.