United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-71: Recent Identified Problems with Limitorque Motor Operators

                                                            SSINS NO.: 6835 
                                                            IN 86-71       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                               August 19, 1986

Information Notice No. 86-71:   RECENT IDENTIFIED PROBLEMS WITH 
                                   LIMITORQUE MOTOR OPERATORS 


All nuclear power reactor facilities holding an operating license or a 
construction permit. 


This notice is provided to alert recipients of two potential problems 
discovered with Limitorque motor operators. It is expected that recipients 
will review this information for applicability to their facilities and 
consider actions, if appropriate, to preclude a similar problem from 
occurring at their facilities. However, suggestions contained in this notice
do not constitute NRC requirements; therefore, no specific action or written
response is required. 

Past Related Documents: 

Information Notice No. 86-03 "Potential Deficiencies in Environmental 
Qualification of Limitorque Motor Valve Operator Wiring," January 14, 1986. 

Description of Circumstances - Burn Damage to Internal Wiring 

On November 8, 1985 Georgia Power Company submitted a preliminary report to 
the NRC indicating that it had discovered burn damage to internal wiring in 
several Limitorque motor operators installed in their Vogtle Unit 1 Power 
Plant. Evidence suggested the burn damage had been caused by electric heater
elements installed in the limit switch compartment for storage purposes 
within certain types of Limitorque motor operators. 

On March 20, 1986 Georgia Power Company submitted a final report to the NRC 
which suggested that the burn damage was a generic problem applicable to all
Limitorque motor operators. This assumption was based on a sampling 
inspection of 104 Limitorque motor operators installed in Vogtle Unit 1. 
Forty-six of the motor operators examined were Limitorque type SMB-000, and 
six of these were found to have burnt internal wiring. Out of the 58 
operators other than type SMB-000 which were inspected, 5 were found to 
contain wires deemed susceptible to damage because of their close proximity 
to the heater elements (less than 1/2 inch). 


                                                           IN 86-71       
                                                           August 19, 1986 
                                                           Page 2 of 3    

On May 20, 1986 an NRC inspector, along with Limitorque, Georgia Power, and 
Bechtel personnel, performed a random inspection on four type SMB-000 
operators installed in Vogtle Unit 2. Three of the four operators were found
to contain burnt internal wiring. One type SMB-00 operator also was 
inspected and was found to contain wiring susceptible to damage. 


The wiring in question is Limitorque installed internal wiring located in 
the operator limit switch compartment. The wiring is being burnt as a result
of its close proximity to, or contact with, the installed limit switch 
compartment electric heater element or heater bracket. The wiring is not 
properly routed and is not restrained from contacting the heater or heater 
bracket. Although the heater is not a seismically or environmentally 
qualified part and is intended for use only during storage, its use has been
shown to cause serious degradation of environmentally qualified internal 

The burnt wiring has been discovered only in Limitorque type SMB-000 motor 
operators that contain previously energized heaters, although any Limitorque
operator that contains a previously energized heater could possibly exhibit 
a similar problem. 

Description of Circumstances - Cracked Limit Switch Rotors 

Several licensees have submitted reports to the NRC concerning a problem 
with cracked limit switch rotors on Limitorque motor operators installed 
inside and outside of containment. The limit switches are used for control 
of the motor operator and also provide indication of valve position in the 
control room. 

The cracks have been found on white melamine limit switch rotors. Most of 
these cracks were found in the area where the limit switch rotors are pinned
to the pinion shafts. Some cracks have been found to extend halfway through 
the melamine rotors, weakening them to the extent that they are easily 


In its letter dated February 21, 1984 to the Westinghouse Electric 
Corporation, Electro Mechanical Division, Cheswick, Pennsylvania Limitorque 
recommended that any white limit switch components which are found with 
cracks should be replaced with components manufactured with a later design, 
brown colored material. Violations of 10 CFR Part 21 have been issued to 
Limitorque for failure to report and for failure to evaluate defects 
discovered in their motor operators. Licensees are reminded of their 
responsibility to ensure that procurement documents include a contractual 
requirement that the provisions of 10 CFR Part 21 apply (when applicable) 
and that Criterion VII of 10 CFR Part 50 Appendix B requires that purchased 
material, equipment, and services conform to the requirements of the 
procurement documents. 

                                                           IN 86-71 
                                                           August 19, 1986 
                                                           Page 3 of 3 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate NRC regional office or this 

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

Technical Contact:  Jeffrey Jacobson, IE
                    (301) 492-8845

Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015