As part of the 1996 NEC revision process, NEMA proposed the inclusion of motor design types in Article 430. Through the efforts of Code-Making Panel 11 and others in the process motor design, types B, C, D and E are now part of the Code and serve as reference points for requirements concerning motors. As a result, UL can now evaluate motor controllers specifically for use with Design E motors. Design E motors are energy-efficient motors that have traditionally been used in Europe and are now becoming more commonplace in North America. They can be used interchangeably in applications where other types of motors have been used in the past.
In addition to the first-time inclusion of these motor design types in the NEC, many of the full-load and locked-rotor current specifications have also changed. It is important not to confuse motor design types with locked-rotor indicating code letters, also in the NEC. UL will revise UL 508, Industrial Control Equipment, again in 1996 to reflect the inclusion of the motor design types and the changes in full-load and locked-rotor current specifications.
Even before this revision takes place, UL can evaluate motor controllers to meet new 1996 NEC requirements (Section 430-83(a), Exception No. 1) for Design E motor controllers. These requirements specify that, in addition to having a "horsepower rating at application voltage not lower than the horsepower rating of the motor," a controller must meet at least one of the following exception criteria: "A controller for a Design E motor rated more than 2 horsepower shall also comply with A or B below:
A. The controller shall be marked for use with a Design E motor
B. The controller shall have a horsepower rating not less than 1.4 times the range of a motor rated 3 through 100 horsepower, or not less than 1.3 times the rating of a motor rated over 100 horsepower."
Item B is referred to as derating based on conversion factors. Controllers that meet these derating requirements do not need to be re-evaluated for use with Design E motors. Compliance with item A can be established by UL evaluating a new controller (or re-evaluating a currently listed controller) and authorizing its manufacturer to use a marking that indicates that the controller is "Suitable for Design E motors."
A controller used with a Design E motor may require more power-handling capability than it would if it were used with a Design B, C, or D motor with the same horsepower rating as the Design E motor. For example, a 10-horsepower controller that is capable of controlling a 10-horsepower Design B motor might not be suitable for controlling a 10-horsepower Design E motor.
Unmarked controllers can generally be used interchangeably with Design B, C and D motors. But, if these same unmarked controllers do not meet either of the NEC requirements (A or B specified above), they cannot be used with Design E motors.
UL evaluation of controllers for use with Design E motors can be an effective way of helping manufacturers and authorities determine which motor controllers are suitable for all motor designs, including Design E, and which are suitable only for Design B, C and D. While UL does not list motors for ordinary locations (non-hazardous locations), it does list controllers, wire, fuses, circuit breakers and many of the products used with controllers.
As UL evaluates new controllers or re-evaluates listed controllers, inspection authorities eventually will begin seeing controllers marked for use with Design E motors. However, only those controllers that bear a UL Listing Mark and the marking "Suitable for Design E motors" should be considered evaluated by UL for that purpose.
In addition, UL has an Energy Verification Service (EVS) to evaluate electric motors and other products for their energy efficiency ratings in accordance with U.S. and Canadian energy efficiency standards. For more information about this program, contact UL's Northbrook, Ill., office at (708) 272-8800, ext. 42848. If you have any questions regarding UL's evaluation of motor controllers based on the 1996 NEC, contact UL's Northbrook, Ill., office at (708) 272-8800, ext 42972 .
