Does anybody know why motors with design letter "E" were dropped from this section?

And while we are here, what is the reason for the special consideration of the design types in this section anyways?

Roger

[This message has been edited by Roger (edited 02-17-2005).]

I heard nobody ever made one.

That's interesting, I must admitt I don't recall ever seeing one.

But what about the second part, why are these particular design types given this allowance?

Roger

I assume you are talking about 430.52.
That just reflects the ratio between normal FLA and LRA. The high effeciency motors evidently have a lower FLA for a given LRA.
It must be a very short LR time since the big difference is in the instant trip breaker column

This was one of approximately two dozen Proposals, all with the same Substantiation


[This message has been edited by rbalex (edited 02-18-2005).]

Let me clarify my secod question.

Why are motors of desing types B,C, or D specifically allowed to use conductors of 75 deg regardless of markings or lack of?

Why would these particular motors be allowed this consideration while other motors would have to comply with the 60 deg limitation for 100 amps or smaller unless marked for higher terminations?

Roger

Roger,

The same question was asked in this forum earlier. The only change to the Section was the elimination of “Design E” motors.

“General Purpose” motors, or as UL refers to them, “motors in ordinary locations,” are not listed; however, if they are designed to NEMA MG-1, their terminals are already suitable for 75C, regardless of the hp.

“Explosion-Proof” motors are listed, but are also generally NEMA Design B, C or D, so they also have terminals that are automatically rated at 75C no matter what hp.

Bob

Hello Bob, and welcome to the forum.

I know that the deletion of the E design was the only change, but as far as my other question, since the terminals are 75 deg and marked, why is it necessary to include this wording in 110.14(C)(1)(a)(4)?

I'm just nitpicking, but it seems as though it is a waste of ink.

Roger

The motor terminals aren't required to be marked (they usually aren't) and the motors themselves aren’t listed; but, if the motor nameplate indicates they are NEMA Design B, C or D, the terminals are suitable for the full ampacity of conductors rated 75C or less.

Bob, I just don't understand why these particular motors are different than all other types as far as temp ratings.

Roger

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.