United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 79-28: Possible Malfunction of NAMCO Model EA180 Limit Switches at Elevated Temperatures

                                                            SSINS No.: 6820 
                                                            Accession No.:

                                UNITED STATES
                          WASHINGTON, D.C. 20555  

                              December 7, 1979 

                                                  IE Bulletin No. 79-28 


Description of Circumstances: 

The NRC has been recently advised through a 10 CFR 21 report from NAMCO 
Controls that a malfunction of a NAMCO Model EA180 stem mounted limit switch
(SMLS) occurred at the Cooper Nuclear Station. Investigation into the switch
failure by the licensee revealed yellow and brown "crystal-like" resin 
deposits on the internal components of the switch. The affected switch is 
located inside the drywell containment at this facility and was being used 
as the replacement switch for an unqualified SMLS previously identified in 
IE Bulletin Nos. 78-04 and 79-01. 

According to the manufacturer, the problem was traced to a batch of top 
cover gaskets of which some were over-impregnated and insufficiently heat 
cured. It has been determined that this condition can leave an uncured 
residue of "Loctite" in the gasket, which vaporizes at sustained 
temperatures above 175oF. To correct the problem, the manufacturer has 
revised production techniques,beginning September 1979 in order to better 
control the impregnation process and to properly heat cure the gaskets 
following impregnation. This problem is unique to all NAMCO Model EA180 
series switches received by licensees after March 1, 1979. According to the 
manufacturer, the suspect switches can be identified by checking the date 
code which is a 4 digit number stamped on the conduit boss of the switch 
housing.  NAMCO recommends that any EA180 series switch with a date code 
between 02-79 through 08-79 should have its top cover gasket replaced. Also, 
licensees should request from their suppliers of equipment on which NAMCO 
EA180 series switches are used that they check their inventory and replace 
top cover gaskets on switches date coded between 02-79 through 08-79. 

The enclosed letter from NAMCO further describes the high-temperature 
environmental problem with the top cover gaskets used in their EA180 
switches and provides recommendations to correct the problem. According to 
NAMCO, this letter has been sent to each customer who was shipped EA180 
switches between February 21, 1979, and August 24, 1979. 

Action to be Taken by Licensees of Power Reactor Operating Facilities and @ 
Holders of Construction Permits: 

1.   Determine if your facility has installed or plans to install NAMCO 
     EA180 switches in any safety-related equipment located inside or 
     outside containment, including valve position indicating circuitry 
     related to containment isolation valves. 
IE Bulletin No. 79-28                                  December 7, 1979 
                                                       Page 2 of 2 

2.   If such switches are identified, examine the four digit number stamped 
     on the conduit boss of the switch housing. If this number falls between
     02-79 and 08-79, replace the top gasket of the switch in accordance 
     with the manufacturer's recommendations provided in the enclosed 

3.   Submit your plans and programs, including schedules for corrective 
     action, regarding your findings in response to Items l and 2 above. 

4.   Provide the response in writing within 30 days for facilities holding 
     an operating license and within 60 days for those holders of 
     construction permits. 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, Washington, 
     D.C. 20555. 

Approved by GAO, B180225 (R0072); clearance expires July 31, 1980. Approval 
was given under a blanket clearance specifically for identified generic 

Extract of NAMCO Controls 
  Letter dated 8/30/79
Page Last Reviewed/Updated Friday, May 22, 2015