NEC 110.14(C)(1) & Type P cable

[lmotloch]

I'm hung up on properly sizing Type P cable (rated for 100C), and explosion proof motor, and a 75C terminal. Ampacity rating for the cable comes from IEEE 45-2002.

Motor FLC	=	6.7	A
		x125	%
Required Conductor Ampacity	=	8.4	A
14 AWG @ 100°C Rating	=	25	A
Derating @ 55°C Ambient		x0.9
Derated ConductorAmpacity	=	22.5	A

As you can see, the cable is way overkill for the actual current requirement, but is the smallest allowable size per NEC 430.22(G). Where I get hung up is the application of 110.14(C), which states that "the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device." I exceed the terminal temp rating at 75C (20A), but will NEVER come close to this current during normal nor overload conditions.

Am I allowed to use this cable, but must consider circuit ampacity to be 20A? Section (C)(1)(a)(4) tells me I can use the cable, provided the ampacity of such conductors does not exceed 75C. This requirement seems to not apply since actual usage will never heat up the terminal.

 

[Carultch]

I'm hung up on properly sizing Type P cable (rated for 100C), and explosion proof motor, and a 75C terminal. Ampacity rating for the cable comes from IEEE 45-2002.

Motor FLC	=	6.7	A
		x125	%
Required Conductor Ampacity	=	8.4	A
14 AWG @ 100°C Rating	=	25	A
Derating @ 55°C Ambient		x0.9
Derated ConductorAmpacity	=	22.5	A

As you can see, the cable is way overkill for the actual current requirement, but is the smallest allowable size per NEC 430.22(G). Where I get hung up is the application of 110.14(C), which states that "the temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device." I exceed the terminal temp rating at 75C (20A), but will NEVER come close to this current during normal nor overload conditions.

Am I allowed to use this cable, but must consider circuit ampacity to be 20A? Section (C)(1)(a)(4) tells me I can use the cable, provided the ampacity of such conductors does not exceed 75C. This requirement seems to not apply since actual usage will never heat up the terminal.

Derated ampacities do not apply to 110.14(C) requirements.

In general, you can use the full rating of the wire, ignoring the equipment and terminations, when you need to calculate conditions of use ampacity. Provided that the termination/equipment ampacity requirement is met (before calculating conditions of use derates).

One unuaul case is Romex. Where even with 75C terminals/equipment and 90C romex, you still have to use the 60C column of the NEC. You can still use the romex temperature rating for conditions of use.

 

[don_resqcapt19]

...
Am I allowed to use this cable, but must consider circuit ampacity to be 20A? Section (C)(1)(a)(4) tells me I can use the cable, provided the ampacity of such conductors does not exceed 75C. This requirement seems to not apply since actual usage will never heat up the terminal.

I am not sure that you can use Type P cable for NEC applications. In general, the conductors used for NEC applications must be listed in the NEC. I don't recall seeing Type P in the NEC.

 

[lmotloch]

I am not sure that you can use Type P cable for NEC applications. In general, the conductors used for NEC applications must be listed in the NEC. I don't recall seeing Type P in the NEC.

Agreed, it's not listed in the NEC but is HEAVILY utilized in the Oil and Gas market, particularly in hazardous areas (NEC 500, 505). A lot of these applications involve putting all electrical components in a thick, AL explosion-proof box out in the middle of the field. If an event were to occur, it is totally contained within the enclosure until it has cleared or something opens upstream. As such, I don't really appreciate how much NEC actually applies, but it provides great guidelines for appropriate conductor, protective, motor sizing etc.

 

[don_resqcapt19]

Agreed, it's not listed in the NEC but is HEAVILY utilized in the Oil and Gas market, particularly in hazardous areas (NEC 500, 505). A lot of these applications involve putting all electrical components in a thick, AL explosion-proof box out in the middle of the field. If an event were to occur, it is totally contained within the enclosure until it has cleared or something opens upstream. As such, I don't really appreciate how much NEC actually applies, but it provides great guidelines for appropriate conductor, protective, motor sizing etc.

In that case, I would have no problem using the conductor as long as it was not loaded more that the ampacity of a 75°C of the same size.