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PrintHome > NRC Library > Document Collections > Generic Communications > Information Notices > 1993 > IN 93-64 Information Notice No. 93-64: Periodic Testing and Preventive Maintenance of Molded Case Circuit Breakers                                 UNITED STATES                         NUCLEAR REGULATORY COMMISSION                     OFFICE OF NUCLEAR REACTOR REGULATION                            WASHINGTON, D.C.  20555                                August 12, 1993NRC INFORMATION NOTICE 93-64:  PERIODIC TESTING AND PREVENTIVE MAINTENANCE                                 OF MOLDED CASE CIRCUIT BREAKERSAddresseesAll holders of operating licenses or construction permits for nuclear powerreactors.PurposeThe U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to the problem of age-related degradation of moldedcase circuit breakers (MCCBs) and to provide sources of information on MCCBperiodic testing and preventive maintenance.  It is expected that recipientswill review the information for applicability to their facilities and consideractions, as appropriate, to avoid similar problems.  However, suggestionscontained in this information notice are not NRC requirements; therefore, nospecific action or written response is required.Description of CircumstancesKewauneeDuring special testing in 1992 of 35 spare Westinghouse Type EB and EHB MCCBsat the Kewaunee Nuclear Power Plant, 10 of the MCCBs tripped late in thermaltrip tests at 300-percent overcurrent and 1 of the 10 failed to trip below themaximum allowable trip current in an instantaneous magnetic trip test. Subsequent testing during the 1992 outage showed a similar percentage of out-of-tolerance MCCBs.  Because the MCCBs were available for use in safety-related and fire protection applications, the licensee reported thecircumstances as an item of generic interest in Licensee Event Report (LER)50-305/92-01.The licensee attributed the out-of-tolerance trip values to age-relateddegradation and infrequent exercising of the MCCBs, some of which had not beenexercised since initial plant startup in 1974.  Sometimes retests weresuccessful after the breaker was exercised manually, which is one type ofpreventive maintenance recommended by manufacturers and industry standards. However, without periodic testing, the degraded condition of the MCCBs was notdetected earlier.  The licensee replaced the Type EB and EHB breakers inservice and plans to implement a program at Kewaunee to test and exercisesafety-related MCCBs periodically starting in August 1993.9308060237.                                                            IN 93-64                                                            August 12, 1993                                                            Page 2 of 3ZionAn NRC diagnostic evaluation team at the Zion Nuclear Station observed thatthe licensee had no program for routinely testing MCCBs (U.S. NuclearRegulatory Commission, "Diagnostic Evaluation Team Report for Zion NuclearPower Station," August 1990).  Many breakers had been in service for more than20 years without being exercised or tested so the potential existed forundetected degradation that could impair the performance of safety-relatedsystems.DiscussionAs a followup to the Zion evaluation, the NRC conducted an industry-wide studyof MCCB performance history, reported in "Review of Operational Experiencewith Molded Case Circuit Breakers in U.S. Commercial Nuclear Power Plants"(June 1992).  The study found that for the analyzed failure modes, most of thefailure rates fell below those estimated generically in The Institute ofElectrical and Electronics Engineers (IEEE) Std 500-1984, "IEEE Guide to theCollection and Presentation of Electrical, Electronic, and Sensing ComponentReliability Data for Nuclear Power Generating Stations."  The study also notedthat, except for limited cases, there are no general technical specificationrequirements for periodic testing and preventive maintenance of safety-relatedMCCBs.  Some plant-specific technical specifications require testing certainMCCBs used only for overcurrent protection for electrical containmentpenetrations, but the testing is limited, and not all of the circuits aresafety-related.  The study found that despite manufacturer recommendations andindustry standards, many plants do not perform periodic testing or preventivemaintenance on safety-related MCCBs, and for the few that do, frequency andprocedures differ widely.In addition, as part of its aging research program, the NRC sponsored a studyreported in March 1992 in NUREG/CR-5762, "Comprehensive Aging Assessment Studyof Circuit Breakers and Relays," that evaluated various inspection,surveillance, and monitoring techniques and preventive maintenance practices. The study found that MCCB preventive maintenance practices (such as manualexercising), can mitigate the effects of aging and help ensure continued MCCBreliability.  However, manual exercising alone was not found effective indetecting or assessing age-related degradation.  Detecting or assessingdegradation, the study found, could only be accomplished through appropriateperiodic testing and monitoring.  Certain standard MCCB tests (such asindividual pole resistance, 300-percent thermal overload, and instantaneousmagnetic trip tests) performed periodically were found effective along withthe additional techniques of infrared temperature measurement and vibrationtesting.An example of the industry standards that address periodic testing andpreventive maintenance is IEEE Std 308-1974, "IEEE Standard Criteria for Class1E Power Systems for Nuclear Power Generating Stations" (endorsed by .                                                            IN 93-64                                                            August 12, 1993                                                            Page 3 of 3Regulatory Guide 1.32, Revision 2, February 1977).  Its Section 6.3 as well asSection 7.4.1 of the current (1991) edition of the standard recommend thatperiodic tests be performed at scheduled intervals to detect the deteriorationof the equipment and to demonstrate operability of the components that are notexercised during normal operation.  Other industry standards and publicationsthat contain recommendations for testing and maintenance of MCCBs include thefollowing: American National Standards Institute (ANSI)/IEEE Std 242-1986, "IEEERecommended Practice for Protection and Coordination of Industrial andCommercial Power Systems" �ANSI/National Fire Protection Association (NFPA) 70B-1990, "RecommendedPractice for Electrical Equipment Maintenance" �National Electrical Manufacturers Association (NEMA) Standard Publication No.AB 4-1991, "Guidelines for Inspection and Preventive Maintenance of MoldedCase Circuit Breakers Used in Commercial and Industrial Applications"  Electric Power Research Institute (EPRI) Report NP-7410, "BreakerMaintenance," Volume 3, "Molded-Case Circuit Breakers," September 1991 The recommendations of these publications may not be applicable in everyinstance, depending on the specific components installed, their functions, andtheir environment.This information notice requires no specific action or written response.  Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.                                    ORIGINAL SIGNED BY                                    Brian K. Grimes, Director                                    Division of Operating Reactor Support                                    Office of Nuclear Reactor RegulationTechnical contacts:  Sikhindra K. Mitra, NRR                     (301) 504-2783                     Stephen D. Alexander, NRR                     (301) 504-2995                     Satish K. Aggarwal, RES                     (301) 492-3829Attachment:List of Recently Issued NRC Information Notices.Page Last Reviewed/Updated Tuesday, November 12, 2013Home- News   Releases
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