1、UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULUNDERWRITERS LABORATORIES CERTIFICATION REQUIREMENT DECISIONThis Certification Requirement Decision is prepared and published by Underwriters Laboratories (UL). Itis normative for the applicable
2、UL Product Certification Program(s); however, it is currently not part ofthe UL Standard(s) referenced below.Product Category (CCN): XEWR, XEIT, XDNW, XDAMStandard Number: UL 2111Edition Date: March 28, 1997Edition Number: 1Section / Paragraph Reference: 7, 8, 9, 14, 15, 16Subject: Power Interruptio
3、n During Locked Rotor Tests on Impedance ProtectedMotors and Motors Containing Automatic Reset Thermal Motor Protectors (TMP)DECISION:Recently, the question was raised, “What is the process to be followed if, due to utility problems, a lockedrotor test is interrupted?”As we know, what is commonly ca
4、lled the Locked Rotor Test is really a combination of two tests: the Locked Rotor Temperature Test (LRTT) 72 Hours and the Locked Rotor Endurance Test (LRET) 15 daysLRTT Interruption of the LRTT for impedance protected motors and motors provided with automaticreset protectors is not permitted (see U
5、L 2111, 7.4 and 14.2.1).LRET Since the LRET is a 15-day test, it is possible (and in some areas of the world, even likely) thatpower to the motor will be interrupted during the 15 days.Consider that, the LRET is really a time and temperature stress on the insulating materials, a stress teston the mo
6、vable parts of the automatic reset protector and a test of the freedom from welding of thecontacts of the automatic reset protector. In each case, the effects are cumulative. In fact, interrupting theLRET represents a somewhat more severe situation for the following reasons:1. The mass of the motor
7、is allowed to cool, all of the materials and components contract andwhen the test is restarted, the materials and components again expand. The cumulative effectsof the time and temperature on the materials are the same but now the added stress of theslight shifting and abrasion that occurs due to th
8、e additional cooling/heating cycle has beenintroduced.2. If one were to graph the test temperatures in the early stages of the test, for a motoremploying an automatic reset protector, you would see some degree of overshoot before thetemperature stabilized and then a steadily decaying cycle of temper
9、ature excursions as the“system” stabilizes. By restarting, this period of overshoot is experienced twice.3. When a motor with its rotor locked is first energized, there is an initial “cold coil inrush” thatoccurs. Again, by restarting, this stress is experienced twice.UL COPYRIGHTED MATERIAL NOT AUT
10、HORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULRATIONALE FOR DECISION:If a LRET is interrupted prior to its completion (15 days) the client is to be given the option of restartingthe test from the beginning with a new sample or continuing the test, with the original motor,
11、 at the pointwhere it was interrupted, until the cumulative 15 days has elapsed.If the test is restarted and the motor complies with the acceptance criteria noted in 9.2, 9.3, 16.1.2 and16.1.3 as appropriate, then the results are to be considered acceptable. If the motor fails to meet one ormore of
12、the criteria, then, at the manufacturers discretion, the test may be repeated with a new sample.Note that if the interruption occurred at the very beginning of the test, it would make good practical senseto start over with a new sample simply because there will be little time wasted and the uncertai
13、nty ofresults and the potential need to retest is avoided.Copyright 2008 Underwriters Laboratories Inc.UL, in performing its functions in accordance with its objectives, does not guarantee or warrant thecorrectness of Certification Requirement Decisions it may issue or that they will be recognized o
14、r adoptedby anyone. Certification Requirement Decisions are the opinion of Underwriters Laboratories Inc. inpractically applying the requirements of the standard. They do not represent formal interpretations of thestandard under American National Standards Institute (ANSI) processes. UL shall not be
15、 responsible toanyone for the use of or reliance upon Certification Requirement Decisions by anyone. UL shall not incurany obligation or liability for damages, including consequential damages, arising out of or in connectionwith the use or reliance upon Certification Requirement Decisions. The electronic version of theCertification Requirement Decision is the current version and previously printed copies may be outdated.This document is published as a service to ULs certification customersSTANDARD NUMBER: UL 2111 -2-
