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#98710 02/17/05 08:00 PM
Joined: May 2002
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Roger Offline OP
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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).]

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#98711 02/17/05 08:03 PM
Joined: May 2004
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R
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I heard nobody ever made one.

#98712 02/17/05 08:33 PM
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Roger Offline OP
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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

#98713 02/17/05 10:38 PM
Joined: Jul 2004
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G
Member
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


Greg Fretwell
#98714 02/18/05 12:24 AM
Joined: Dec 2004
Posts: 12
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Member
Quote
11-16 Log #2308 NEC-P11
(430-7(A)(9))
Final Action: Accept
Submitter: Vince Baclawski, National Electrical Manufacturers Association (NEMA) / Rep. NEMA
Recommendation:
Revise as shown below:
(9) Design letter for design B, C, or D, [or E deleted] motors.
Substantiation:
The Design E motor standard was rescinded by NEMA in February 2000. All references to Design E motors have been removed from NEMA Standards Publication MG 1-1998 "Motors and Generators".
This was one of approximately two dozen Proposals, all with the same Substantiation


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

#98715 02/18/05 10:08 AM
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Roger Offline OP
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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

#98716 02/18/05 12:23 PM
Joined: Dec 2004
Posts: 12
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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

#98717 02/18/05 01:05 PM
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Roger Offline OP
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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. [Linked Image]

Roger

#98718 02/18/05 02:52 PM
Joined: Dec 2004
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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.

#98719 02/18/05 03:36 PM
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Roger Offline OP
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Bob, I just don't understand why these particular motors are different than all other types as far as temp ratings.

Roger

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