Information Notice No. 84-29: General Electric Magne-blast Circuit Breaker Problems

                                                       SSINS No.:  6835 
                                                       IN 84-29 

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 

                               April 17, 1984 



All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 


This information notice is being issued to inform the license and 
construction permit holders of a potential generic problem concerning 
wornout sleeve bearings that recently have caused circuit breaker closure 
failures at the Diablo Canyon nuclear station. Information also is presented 
on recommended actions by the breaker manufacturer (GE)*. These actions, if 
implemented, can significantly alleviate the cause of the wear problem in 
the breaker sleeve bearing. It is expected that recipients will review the 
information for applicability to their facilities and consider actions, if 
appropriate, to preclude a similar problem occurring at their facilities. 
However, suggestions contained in this information notice do not constitute 
NRC requirements and, therefore, no specific action or written response is 


Many nuclear power plants use a substantial number of the GE Magne-Blast 
circuit breakers with the M-13 operating mechanism on 4kV systems. The M-13 
operating mechanism employs a Tuf-Loc sleeve bearing that consists of 
teflon-coated fiberglass. A few cases involving a more-than-normal-wear 
condition of the Tuf-Loc sleeve bearing, were reported by GE as early as 

To minimize the possibility of a circuit breaker problem and to increase the 
life of the sleeve bearings, GE issued the referenced Service Advice letters 
to the end-users. The letters identified the problem and provided corrective 
actions to resolve the issue. At that time, GE recommended that customers 
"promptly and regularly" inspect the breaker for excessive play and wear of 
the bearings in the linkages and pawls and for difficulty in holding the 
required breaker adjustments including the contact wipes to the breaker. GE 
also recommended replacement of the Tuf-Loc bearings with the longer life 
and more 

*General Electric Installation and Service Engineering Service Advice 
Letters; Numbers 318.1 (February 17, 1977), 318.1A (March 29, 1977), and 
318.2 (March 22, 1979); subject: ML-13 Mechanism Sleeve Bearing Replacement.


                                                            IN 84-25 
                                                            April 17, 1984 
                                                            Page 2 of 2 

suitable Aluminum Bronze bearings. According to GE the Aluminum Bronze 
bearing design was qualified and introduced into similar applications of all 
new breakers of the Magne-Blast type since 1975. 


A licensee recently reported experiencing "more than normal wear" on one of 
its Magne-Blast breakers. Subsequently, one of the emergency diesel 
generator output breakers (Magne-Blast type) failed to close during a test. 
Investigation into the failure revealed that the teflon sleeve bearing was 
deteriorated to the point of metal-to-metal contact. Further investigation 
into the problem, found that the licensee had no record of receiving the GE 
Service Advice letters related to this problem. Subsequently, the licensee 
received the GE letters and has now initiated a replacement program for 
Magne-Blast circuit breakers. Since the licensee has initiated the 
replacement program, two additional breaker failures that are related to the 
bearing wear problem have been found. 

In contrast, another licensee stated that they replaced the teflon sleeve 
bearing several years ago with the Aluminium Bronze bearing in all safety-
related Magne-Blast circuit breakers. This licensee indicated that the re-
placement program was initiated after receiving the GE Service Advice 
letters on the sleeve bearing issue and experiencing bearing wear problems 
in the Magne-Blast circuit breakers at their facility. Approximately 80 
Magne-Blast circuit breakers, 40 per unit, were involved in the sleeve 
bearing replacement effort. Their operating experience has been good 
subsequent to the bearing replacement. 

To ensure that all nuclear power plants are aware of the GE Service Advice 
letters pertaining to this issue, we request all licensees and holders of 
construction permits to review this notice and the referenced GE letters for 
applicability to their plant and to take appropriate action. 

If you have any questions regarding this matter, please contact the Regional 
Administrator of the appropriate NRC Regional Office, or this office. 

                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                        and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  V. D. Thomas, IE 
                    (301) 492-4755 

1.   GE Service Advice Letter No. 318.1 
2.   List of Recently Issued IE Information Notices 

Page Last Reviewed/Updated Wednesday, March 24, 2021