United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No.80-13 – General Electric Type SBM Control Switches Defective Cam Followers

                                                          SSINS No.: 6870  
                                                          Accession No.:   
                                                          8002280650       

                                UNITED STATES
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D.C. 20555  
                                     
                               April 2, 1980  

                                            Information Notice No. 80-13 

GENERAL ELECTRIC TYPE SBM CONTROL SWITCHES DEFECTIVE CAM FOLLOWERS 

Description of Circumstances: 

This Information Notice alerts licensees and holders of construction permits
of a potential defect in the cam followers of General Electric (GE) Type SBM
control switches. Based on preliminary information, it appears that the 
defect is limited to switches manufactured prior to 1976 with cam followers 
of polycarbonate material, such as Lexan. In brief, the problem is initiated
by exposing such polycarbonate material to hydrocarbons. Such exposure leads
to severe cracking having a rock salt appearance which ultimately could 
progress to mechanical failure. It has been determined that such exposure 
has occurred during fabrication and could occur while performing maintenance
(e.g. cleaning the contacts). 

On February 22 and March 10, 1980 we were informed that SBM switches with 
defective cam followers had been found at Diablo Canyon Unit 1 and at the 
Cooper Station, respectively. Although the information was preliminary and 
sketchy, the problem is a long-standing one for which GE has issued "Service
Information Letters" to its BWR customers. The problems associated with such
switches, however, are not restricted to GE customers as evidenced by the 
Diablo Canyon case. Furthermore, these switches have a broad range of 
application. For example, the defective switches at the Cooper Station were 
used principally as hand control switches, most of which were located in the
control room. In contrast, those at Diablo Canyon Unit 1 were used as 
auxiliary contacts on the 4KV and 12KV "Magna Blast" circuit breakers, with 
three SBM switches used per breaker: (1) a breaker mounted auxiliary switch,
(2) a cell mounted auxiliary switch, and (3) a cell interlock switch. 

This information is provided as notification of a possibly significant 
matter that is still under review by the NRC staff. It is expected that 
recipients will review the information for possible applicability to their 
facilities. No specific action or response is requested at this time. If you 
have questions regarding this matter, please contact the Director of the 
appropriate NRC Regional Office. 

Page Last Reviewed/Updated Tuesday, November 12, 2013