United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-08: Degraded Motor Leads in Limitorque DC Motor Operators

                                                        SSINS No.: 6835 
                                                          IN 87-08

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                              February 4, 1987

Information Notice No. 87-08:   DEGRADED MOTOR LEADS IN LIMITORQUE DC 
                                   MOTOR OPERATORS 


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


This notice is provided to alert recipients of potentially defective dc 
motors installed in Limitorque motor operators. The motors in question were 
manufactured at H. K. Porter (now Peerless-Winsmith) between December 1984 
and December 1985. The motors are fitted with Nomex-Kapton insulated leads 
that are susceptible to insulation degradation and subsequent short circuit 
failure. The Nomex-Kapton leads are different than the leads which were 
tested and reported in Limitorque Qualification Report B-0009 dated April 
30, 1976. Valves with these Nomex-Kapton leads have recently failed to 
actuate on demand at two nuclear plant sites. 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. 

Description of Circumstances: 

On May 6, 1986 the NRC received from Portland General Electric Company a 10 
CFR 21 report concerning a motor failure which occurred at its Trojan 
Nuclear Power Plant. The failure involved shorting of the motor leads inside 
a Limitorque motor operator connected to an auxiliary feedwater flow control 
valve. Upon inspection it was determined that the failure was the result of 
insulation degradation of the motor leads that had allowed two leads to 
short together. Further, inspection at Trojan revealed three similar motors 
that also had experienced insulation degradation. 

Recently, the NRC has also learned of a failure at the Turkey Point Nuclear 
Power Plant in which the steam supply valve for the auxiliary feedwater 
turbine failed to operate after a Limitorque motor operator experienced a 
similar motor lead short circuit. The Trojan and the Turkey Point Limitorque 
operators were found to contain motors manufactured with Nomex-Kapton 
insulated leads. 


                                                       IN 87-08 
                                                       February 4, 1987
                                                       Page 2 of 3     

On January 12-14, 1987, the NRC conducted an inspection at 
Peerless-Winsmith, Inc., manufacturer of dc motors for Limitorque Co. During 
this inspection it was determined that the failed Nomex-Kapton leads were 
different than the leads which were fitted to the motors, tested, and 
documented in Limitorque Qualification Report B-0009 for dc motor operators. 
The leads attached to the tested motors were insulated with Nomex plus an 
epoxy impregnated braided fiberglass sleeve. The NRC knows of no analysis or 
testing that has been performed to show the Nomex-Kapton leads are 
acceptable for use in an application requiring environmental qualification. 
Further, it should be noted that the failures cited above occurred under 
normal operating conditions, not under the harsh conditions which could 
occur in areas where environmental qualification is required. 

On December 19, 1986, Limitorque notified 30 plant sites (Attachment 1) that 
had received affected motors and recommended the sleeving of existing 
Nomex-Kapton motor leads. The sleeving system is still under development and 
Limitorque expects to have this system tested for environmental 
qualification by the third quarter of 1987. 

Discussion: The Peerless-Winsmith motors were manufactured between December 
1984 and December 1985 and can be identified by the first two letters of the 
serial number data code on the motors. Motor serial numbers beginning with 
the letters ZM, NN, PN, QN, RN, SN, TN, UN, VN, WN, XN, YN, and ZN likely 
contain the Nomex-Kapton leads. The lead insulation consists of one layer of 
50 percent overlapped 0.003 inch Nomex plus a 50 percent overlapped layer of 
0.0012 inch F616 Kapton/FEP. This insulation system is about one-sixth the 
thickness of the leads which were part of the Limitorque qualified motor. 
Peerless-Winsmith has since switched to a third type of insulated lead 
similar to the ones used originally. No failures with this type of lead have 
been reported; however, qualification of this type wire also needs to be 

Previous, unrelated problems involving wiring installed in Limitorque motor 
actuators have been identified in Information Notices 83-72, 86-03 and 

Although no written response to this notice is required, it is expected that 
holders of OLs or CPs will review the information in this notice for 
applicability at their facilities. Because of the failures such as those 
discussed above and the lack of demonstrated environmental qualification, 
NRC's evaluation of this problem is continuing. Depending on the result of 
the evaluation, specific actions may be requested. If you have any questions 
regarding this

                                                       IN 87-08 
                                                       February 4, 1987
                                                       Page 3 of 3

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:  J. Jacobson, IE
                    (301) 492-8845

1.   List of Affected Plants
2.   List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015