Why Does the Code Mention Design E Motors If No One Makes Them?

My business is to conduct seminars on the National Electrical Code (NEC), grounding and bonding, and electrical safety. Even before it went into effect, questions arose in the seminars about coverage of Design E motors in the 1996 NEC. Before its issue, I attended a seminar concerning the changes to 1996 NEC. When I asked a featured speaker for information about Design E motors, his answer should have warned me, “Houston, we have a problem.” He related people’s anger toward the Code makers, saying, “I don’t know what they’re going to do about it, issue an errata or wait until the new Code cycle.” Do about what? I just wanted an explanation of this motor’s characteristics so I could address questions about the Article 430 references to this motor. The first mention was at Section 430-7(a)(9), which stated that, “a motor shall be marked with the following information…Design letter for design B, C, D, or E motors.” Section 430-52 Rating or Setting for Individual Motor Circuit mentions in Section 430-52(c)(3) that, concerning Motor Branch-Circuit Short-Circuit and Ground Fault Protection, the exception allows us to increase an instantaneous trip breaker’s settings if the setting listed in Table 430-152 for Design E motors is insufficient for the starting current of the motor. Sections 430-83 and 430-109 mention that we may have to increase the size of a motor controller or disconnect switch by 1.4 or 1.3 times the horsepower rating (the HP motor rating determines which figure we use), if we are using a Design E motor. A fine print note (FPN) at 430-7(a)(9) related that these Design letter definitions could be found in the NEMA MG 1-1993 and in the Standard Dictionary of Electrical and Electronic Terms, ANSI/IEEE 1992. I decided the Design E motor manufacturers or salespeople would be a better information source. But when I called GE, Toshiba, Baldor, Lincoln, and several others, I was told, “We don’t make such a motor, ours is of other design with such and such efficiency.” I e-mailed a few individuals at NFPA. One response was, ‘If you don’t like what the Code says, submit a proposal to change it.’ I felt that a mistake warranted an erratum, not a proposal. I started calling the Code-making panel members responsible for Article 430. The first gentleman I spoke with told me, “We’ve been had.” He explained that they thought the industry was going to go that way. I then ordered the NEMA MG 1-1998 Motor and Generator book, in which Design E was still listed. I was surprised because my investigation so far indicated that there is no such thing as a Design E motor. To add to the confusion though, in September 1999, I read an EC&M article entitled “Design E Motor: You May Have Problems.” I thought, at last someone will solve this mystery. This article told about the potential problems with Design E relating to torque, and analyzed whether or not you wasted money on a motor that may not fill your needs. After reading that article, I attempted to contact the author and EC&M’s Editor-In-Chief John A. DeDad, who refused to return my calls. In 1996 the NEC made a big change on the positive side in Table 430-152, Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protection Devices. It was greatly simplified, with Code letters being done away with on squirrel-cage motors. Prior to the 1996 NEC, Table 430-152, listed for polyphase motors all the Code letters, and the different settings allowed for these various motors. In 1996 it was greatly simplified, or so I thought, by defining polyphase motors as being either “Design E,” or “Other than Design E.” The mystery was where to find this Design E motor, other than in the Code. Other publications ran articles on how to comply with the Code when installing a Design E motor. Oh well, I thought, the 1999 Code will surely clear the mystery up. I had no time to submit a proposal and reasoned that, by now, most people on the Code committee for Article 430 knew more about it than I did and realized there was no such thing as a Design E motor. But then, my advance copy of the 1999 NEC seemed to repeat all the sections mentioning the specifics for Design E motors. I thought I was going mad. Could someone sell me this motor or not? Finally, my suspicions have been confirmed: I learned in December 2000 that on February 9, 2000, the NEMA Codes and Standards Committee approved a request from the Motor and Generator Section to rescind the NEMA standard covering Design E motors. The official letter is available from this writer or from NEMA. They have admitted that all the NEC requirements have created confusion because this motor never really left the Research and Development stage. They are not the motors the EPAct requires. This EPAct originated in 1992, with a requirement that all motors between 2 and 200 Horsepower, of a Design A and B, be energy efficient. This requirement was to go in to effect November 1, 1997. Exactly which motors are involved in the EPAct mandate, and what the Code requirements are for these energy-efficient motors, if any, is a future story. But the mystery will continue, because they are still included in the 2002 NEC. We will have to wait to see if we finally get an erratum or if we must wait until the 2005 NEC. But the mystery is solved, and yes, Virginia, there really is no Design E motor. CORCORAN is a Code consultant for EMC Code Consultants in Burlington, Wash. He can be reached at (360) 757-3605.

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