Nec 240.4

[erickench]

Was teaching a seminar today and the question came up. Let's suppose you have a motor circuit with 18A which includes the 125% factor flowing through it. According to NEC table 310.16 the ampacity of No. 14 AWG is 20A at 75'C. However, NEC 240.4(D)(2) state's that 14 AWG must be protected at 15A. According to 240.4(B) the next higher standard OCPD is permitted to be used under certain conditions. We have 18A flowing through the circuit so the next higher OCPD rating would be 20A.

Question: Can we use a 20A OCPD for a No. 14 AWG at 75'C for this motor circuit?

 

[Dennis Alwon]

240.4(D) excludes 240.4(G) so 240.4 (G) allows it

 

[erickench]

One more thing the 18A calculation includes the 125% factor.

 

[erickench]

240.4(D) excludes 240.4(G) so 240.4 (G) allows it

Yes I think so too. I didn't think of it when somebody asked the question today.

 

[xformer]

240.4(D) excludes 240.4(G) so 240.4 (G) allows it

I agree with Dennis..

 

[Dennis Alwon]

14 awg is good for 20 amps even at 60C at least until 2011 is adopted then it is still good for 20 amps at 75C. Motors and a/c and everything in 240.4(G) are not limited to 240.4(D) restrictions.

 

[raider1]

I agree with Dennis.

Question: Can we use a 20A OCPD for a No. 14 AWG at 75'C for this motor circuit?

When dealing with motor circuit you need to read and understand Article 430.

For a motor with an 18 amp FLC you can use a 45 amp circuit breaker to provide the short circuit and ground fault protection required by Part IV of Article 430.

What type of seminar were you teaching?

Chris

 

[erickench]

I was teaching P.E. continuing education seminars in New York City. Teaching is new to me and I'm still trying to get the hang of it. The two seminars covered Emergency/Standby systems and Remote/Control/Signaling circuits.

 

[Goroon]

Question: Can we use a 20A OCPD for a No. 14 AWG at 75'C for this motor circuit?

Question: Can we use a 20A OCPD for a No. 14 AWG at 75'C for this motor circuit?

The answer.. for my classes, Yes but only for a Motor Branch circuit
I explain it like this.

Start at 430.1 Scope , This article covers motors, motor branch-circuit and feeder conductors and their protection?.

Go to 430.21 The provisions of Articles 250, 300, and 310 shall not apply to conductors that form an integral part of equipment,

Go to 430.31, ?. overload devices intended to protect motors, motor-control apparatus, and motor branch-circuit conductors against excessive heating?

Go to 430.51 ? against overcurrent due to short circuits or ground faults. These rules add to or amend the provisions of Article 240?.

Finial . With 240 branch circuit you are supplying an ?Over Current? device for excessive heating, while in a motor circuit you supply an ?Over Load ? device for excessive heating.. two different devices, different reaction times and curves.

The OCPD in your statement in a motor circuit is a ?Short Circuit?, ?Ground Fault? additional protection for Motor circuit, having the ?Overload? device for normal excessive currents. Unlike all motors the other ?Ground Fault? requirement is for 1,000 amp services.

Here is where I stress the importance of NOT turning or setting O.L.'s to max just because they trip.

 

[electures]

Was teaching a seminar today and the question came up. Let's suppose you have a motor circuit with 18A which includes the 125% factor flowing through it. According to NEC table 310.16 the ampacity of No. 14 AWG is 20A at 75'C. However, NEC 240.4(D)(2) state's that 14 AWG must be protected at 15A. According to 240.4(B) the next higher standard OCPD is permitted to be used under certain conditions. We have 18A flowing through the circuit so the next higher OCPD rating would be 20A.

Question: Can we use a 20A OCPD for a No. 14 AWG at 75'C for this motor circuit?

Depending on what type of OCPD is used, it could go as high as 60A.

 

[bob]

Was teaching a seminar today and the question came up. Let's suppose you have a motor circuit with 18A which includes the 125% factor flowing through it. According to NEC table 310.16 the ampacity of No. 14 AWG is 20A at 75'C.We have 18A flowing through the circuit so the next higher OCPD rating would be 20A.

Question: Can we use a 20A OCPD for a No. 14 AWG at 75'C for this motor circuit?

A 20 amp breaker will not likely be large enough to handle the starting. You may legally go to a 40 amp.