United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-05: Malfunctioning of Circuit Breaker Auxiliary Contact Mechanism - General Electric Model CR105X

                               UNITED STATES 
                          WASHINGTON, D. C. 20555 
                              April 14, 1978  

                                                     IE Bulletin No. 78-05 


Description of Circumstances: 

The Sacramento Municipal Utility District recently reported a problem 
encountered with the operation of the GE Model CR105X auxiliary contact 
mechanism installed in a 480 volt circuit breaker. Investigation into the 
cause for the inability to shutdown a booster supply fan (SF-A-7) in the 
control room emergency air conditioning system revealed that an auxiliary 
contact (GE Model CR105X) had failed in the closed position, preventing the 
fan's power supply circuit breaker from opening. The specific cause for 
failure was binding of the plunger arm due to burrs and nicks on its 

An investigation was conducted by the licensee to determine the extent of 
usage of this type auxiliary contact in other circuits throughout the 
reactor power plant. Approximately fifty (50) positions in the nuclear 
service motor control centers were identified as having a similar type 
auxiliary contact mechanism. It was also determined that many of the 
affected systems which require contact operation similar to that described 
above, either permit or provide a safety feature function during emergency 
conditions. An example of this type application is auxiliary contacts that 
must open to permit closing of certain safety related valves from 480 volt 
motor control centers. 

The attached GE Service Advice Letter and associated instruction/drawing 
sheet were sent to all nuclear power reactor facilities by GE Field Service 
Offices. The letter, together with the instruction/drawing sheet identifies 
the problem and provides the recommended corrective action. 

Action To Be Taken By Licensees: 

For all power reactor facilities with an operating license or construction 

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IE Bulletin 78-05                                          April 14, 1978 

1.   If you have received the enclosed General Electric letter and 
     instruction/drawing sheet addressing the auxiliary contact mechanism 
     problem, and if you have these devices in use at your facility, it is 
     requested that you describe what corrective action you have taken. 

2.   If you have not received the enclosed GE documents before, it is 
     requested that you describe what action you plan to take if the GE 
     CR105X auxiliary contact mechanism is in use or planned for use in 
     safety systems at your facility(ies). 

3.   Facilities having an operating license should report in writing, within
     45 days, and facilities with construction permits within 60 days, the 
     results of action taken or planned with regard to Items 1 and 2 above. 
     Your written reply should also include the date when such actions were 
     or will be completed. Reports should be submitted to the Director of 
     the appropriate NRC Regional office and a copy should be forwarded to 
     the U. S. Nuclear Regulatory Commission, Office of Inspection and 
     Enforcement, Division of Reactor Operations Inspection, Office of 
     Inspection and Enforcement, Washington, D, C, 20555. 

Approved by GAO, B180225 (R0072); clearance expires 7/31/80. Approval was 
given under a blanket clearance specifically for identified generic 

1.   GE Letter 
2.   GE Control and Instruction 

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