240.4.D and 240.4.G

[tony_psuee]

I need clarification on application of 240.4D. I am working on a new test stand running motor loads of just under 25A. Using the 125% factor and current rating in table 310.17, 75C, I come up with #12AWG. However the circuit protection will be greater than 20A listed in 240.4.D. I have been challenged on that and have countered with 240.4.G and protecting per Article 430. The response back is, ?well we never used #12AWG with anything above a 20A breaker and you are wrong.? Am I correctly applying 240.4.D? I have trouble with, "that's the way we always did it" as an acceptable answer.

Thanks,
Tony

 

[charlie]

Re: 240.4.D and 240.4.G

As long as the voltage drop is acceptable, there is nothing wrong with using #12 on an overcurrent device larger than 20 amperes. That is why the table 240.4(G) is in place.

The reality is that the Motor Branch-Circuit Short-Circuit and Ground-Fault Protection is not sized for overload. The load on the circuit conductors is limited by the motor overload protection.

 

[curtis]

Re: 240.4.D and 240.4.G

Why are you using Table 310.17?

 

[abode electric]

Re: 240.4.D and 240.4.G

I'm having a fight with an inspector (again after getting a letter from the state saying it's acceptable) about this very same thing. He has told me to go back and read the code because #12 is only good for 20 amps including AC wiring. I have yet to come across it in my code book. The next time I talk to him I'm going to ask him to find what code section changes the 25 amps in table 310.16. If any knows of such a section please share with us.

 

[charlie b]

Re: 240.4.D and 240.4.G

Originally posted by abode electric: He has told me to go back and read the code because #12 is only good for 20 amps including AC wiring.

If an Inspector (or anyone else for that matter) just states that a #12 is only good for 20 amps, then that person is almost certainly ?remembering? (also known as ?remembering wrong?) the information in 240.4(D). However, your Inspector is probably not taking into account the opening words of article 240.4(D): ?Unless specifically permitted in 240.4(E) through (G),. . .? As ?the other Charlie? has mentioned, 240.4(G) would apply in the case that you have described.

The next time I talk to him I'm going to ask him to find what code section changes the 25 amps in table 310.16.

240.4(D) does not ?change? the amps in 310.16, but rather inserts one additional set of restrictions.

 

[iwire]

Re: 240.4.D and 240.4.G

240.4(D) says nothing about the rating of the conductors.

All it tells us is what size OCPD to use in applications not spelled out by 240.4(G)

 

[tony_psuee]

Re: 240.4.D and 240.4.G

Curtis - I'm using 310.17 because the wiring will be in a test stand enclosure, so the free air current rating. The wiring for the production test of the equipment motors will be heavy duty cord and per 400.5.


Thanks all for your prompt and useful feedback. Although I am more a lurker than an active contributor this board has been a tremendous resource for me.

Thanks again,

Tony

 

[don_resqcapt19]

Re: 240.4.D and 240.4.G

Tony,
What are you using for motor overload protection? Are all of the motors the same horsepower? If they are not do you change the overload protection to match the motor?
Don

 

[tom baker]

Re: 240.4.D and 240.4.G

"The next time I talk to him I'm going to ask him to find what code section changes the 25 amps in table 310.16. If any knows of such a section please share with us.'

240.3 (G) is overcurrent protection for specific conductor applications, and states "shall be permitted to be provided as referenced in Table 240.4(G)"
You then look at the table for the specific article part that allows a different overcurrent protection from 240.3 D

 

[tony_psuee]

Re: 240.4.D and 240.4.G

Don,

Motor HP varies, however on multi-motor equipment all motors are the same HP. The motors either have internal thermal, or we supply listed 508E motor protectors. The overload protection is changed to match the motor load(s) being tested.

Tony

 

[don_resqcapt19]

Re: 240.4.D and 240.4.G

Tony,
The reason that I ask is because if you did not have motor overload protection, then the branch circuit OCPD would have to provide this protection and then you would not be able to use the #12 on a branch circuit protector larger than 20 amps.
Don