ECN Forum Forums Code Related Discussion NEC & other Code issues 110.14(C)(1)(a)(4)

AH, now I think I get your question.

They aren't different; in fact, Design B is just about the most common general-purpose motor out there. You probably work with them more than any other motor that isn't an integral part of an appliance.

They are neither listed nor “recognized components” (backward UR). They aren’t subject to any UL standard – strictly NEMA. The rest of 110.14 is generally based on UL requirements.

Thanks Bob, but I still don't know why these types are special in wiring methods as compared to other types of motors.

BTW, I probably should have just posted in Elzappr's thread but thought I'd opt for a fresh start.

Roger

Hello Bob, and welcome

Hi All, Thanks for the welcomes

I guess I can only say terminations at the motor for circuits rated 100 amps or less for NEMA Design B, C or D motors don’t have to use a 60C conductor ampacity [110.14(C)(1)(a)(1)&(2)] or have the terminals marked for 75C [110.14(C)(1)(a)(3)]

There’s nothing special about the motors, they are the most common industrial motors out there. They just aren’t subject to UL standards that would limit their terminations to 60C conductor ampacities without additional markings.

Ok, I think we can ignore the issue of 'what about the design E motors?'
The way I see it, it seems to come down to a question of why they don't include 'design A' motors. From what little I've gleaned about the subject, design A motors don't have a defined inrush draw. They are a sort of wild card, as far as design is concerned, with no limit as to the inrush current it might draw. It presents a problem because, as I read somewhere, you have to install it and see what inrush you get before you can properly size your disconnects, etc. ..which is a bit unrealistic. Anyway, since design B and C and D have a constrained and characterizable inrush, then the NEC can safely specify that it is ok to use 75C ampacity wiring, assuming that the 75C will be cooler than the motor leads (which we all know are usually very hot), and so won't lead to overheating the connections, etc. Of course, there is still the question of what happens at the source end termination.