UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                February 27, 1989


Information Notice No. 89-21:  CHANGES IN PERFORMANCE CHARACTERISTICS 
                                   OF MOLDED-CASE CIRCUIT BREAKERS


Addressees: 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose: 

This information notice is being provided to alert addressees to an observed 
practice in which vendors make changes to the performance characteristics of 
molded-case circuit breakers without making any corresponding revisions to 
the breaker part number.  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 do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

During several inspections performed by the NRC, it was discovered that manu-
facturers of molded case circuit breakers frequently altered the time-current 
characteristic curves pertaining to a particular style or type of breaker.  
These changes were made without changing the part number of the breaker and 
often without any specific notification to the customer.  The changes identi-
fied during the NRC inspections ranged from very minor alterations to the 
thermal portion of the curves to major alterations to the magnetic instanta-
neous trip portion of the curves.  One change for ITE-type 100-amp breakers 
involved the movement of the instantaneous band from 600-1000 amps to 
1200-2000 amps.  Although product literature usually contains the appropriate 
curves, the curves are not routinely provided with the breakers. 

Discussion: 

As a result of these changes, many licensees who procure replacement breakers 
by part number only are receiving breakers with performance characteristics 
that may be different from those assumed in the original plant design.  If the 
breakers are not analyzed for performance characteris-tics, upon installation 
these breakers potentially could degrade the electrical protection system 
and/or cause premature tripping upon the energizing of vital safety-related 
systems.  Additionally, many perceived failures of circuit breakers detected 



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                                                            February 27, 1989 
                                                            Page 2 of 2 


during pre-installation or routine testing may actually be the result of un-
known changes in time-current characteristic curves.  One way to ensure that 
the breakers purchased conform to a particular curve would be to reference 
the specific curve (including the applicable revision) as part of the purchase 
requirements.  If the breaker was no longer manufactured to meet the specifi-
cations of that specific curve, the new curve would have to be analyzed for 
its effect on the overall system.  

No specific action or written response is required by this information notice.  
If you have any questions about this matter, please contact the technical 
contact listed below or the Regional Administrator of the appropriate regional 
office. 




                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical Contact:  J. B. Jacobson, NRR
                    (301) 492-0996 

Attachment:  List of Recently Issued NRC Information Notices
..                                                            Attachment 
                                                            IN 89-21
                                                            February 27, 1989
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-73,         Direction-Dependent Leak      2/27/89        All holders of OLs
Supplement 1   Characteristics of Contain-                  or CPs for nuclear
               ment Purge Valves                            power reactors.

89-20          Weld Failures in a Pump       2/24/89        All holders of OLs
               of Byron-Jackson Design                      or CPs for nuclear
                                                            power reactors.

89-19          Health Physics Network        2/23/89        All holders of OLs
                                                            or CPs for nuclear
                                                            power reactors, and
                                                            the following fuel
                                                            facilities:  
                                                            Nuclear Fuel 
                                                            Services of Erwin, 
                                                            General Atomic, UNC
                                                            Montville, B&W LRC
                                                            Lynchburg, and B&W
                                                            Lynchburg.

89-18          Criminal Prosecution of       2/22/89        All holders of OLs
               Wrongdoing Committed by                      or CPs for nuclear
               Suppliers of Nuclear                         power reactors.
               Products or Services

89-17          Contamination and Degra-      2/22/89        All holders of OLs
               dation of Safety-Related                     or CPs for nuclear
               Battery Cells                                power reactors.

89-16          Excessive Voltage Drop        2/16/89        All holders of OLs
               in dc Systems                                or CPs for nuclear
                                                            power reactors.

89-15          Second Reactor Coolant Pump   2/16/89        All holders of OLs
               Shaft Failure at Crystal                     or CPs for nuclear
               River                                        power reactors.

89-14          Inadequate Dedication         2/16/89        All holders of OLs
               Process for Commercial                       or CPs for nuclear
               Grade Components Which                       power reactors. 
               Could Lead to Common Mode
               Failure of a Safety System
__________________________________________________________________________________
OL = Operating License
CP = Construction Permit 
..