Bulletin 78-05: Malfunctioning of Circuit Breaker Auxiliary Contact Mechanism - General Electric Model CR105X
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
April 14, 1978
IE Bulletin No. 78-05
MALFUNCTIONING OF CIRCUIT BREAKER AUXILIARY CONTACT MECHANISM - GENERAL
ELECTRIC MODEL CR105X
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
surface.
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
permit:
1 of 2
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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
problems.
Attachments:
1. GE Letter
2. GE Control and Instruction
Sheet
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Page Last Reviewed/Updated Tuesday, March 09, 2021