United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-43: Mechanical Interference with Thermal Trip Function in GE Molded-Case Circuit Breakers

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C. 20555

                                June 29, 1990


Information Notice No. 90-43:  MECHANICAL INTERFERENCE WITH THERMAL TRIP
                                   FUNCTION IN GE MOLDED-CASE CIRCUIT 
                                   BREAKERS


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is intended to alert addressees of a manufacturing 
deviation in certain General Electric (GE) molded-case circuit breakers 
(MCCBs) which may result in mechanical interference with the thermal 
overcurrent trip function when internal accessory undervoltage release (UVR) 
devices are installed.  In addition, the information contained herein is 
intended to emphasize the importance of conducting thorough pre-installation 
testing to verify that plant components meet the functional performance 
requirements of their safety-related applications.  It is expected that 
recipients will review the information for applicability to their facilities 
and consider actions, as appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances:

In 1989, General Public Utilities-Nuclear (GPUN), the licensee for the 
Oyster Creek Nuclear Power Plant (Oyster Creek), purchased 170 TED-type and 
THED-type MCCBs from GE Nuclear Energy in San Jose, California.  The MCCBs 
were purchased as safety-related items and were supplied with GE Nuclear 
Energy product quality certificates (PQCs).  GE Nuclear Energy purchased the 
MCCBs as commercial grade items (CGIs) from the GE Electrical Distribution 
and Control Department in Plainville, Connecticut (GE-ED&C), who 
manufactured the MCCBs at their Humacao, Puerto Rico, factory and installed 
UVRs at their accessory installation facility in Mascot (Knoxville), 
Tennessee.  The MCCBs were dedicated by GE Nuclear Energy for use in  
safety-related applications at Oyster Creek, in part, on the basis of 
testing performed at the Puerto Rico factory.

In November 1989, one 15-ampere TED-type MCCB from this order was 
bench-tested at Oyster Creek prior to installation.  This MCCB had a UVR 
installed in the standard location by phase "C" (right-hand side).  The MCCB 
failed to trip when 300-percent of rated current was applied to phase C of 
the MCCB (a time-overcurrent test of the thermal trip function), whereas on 
phases A and B, 



9006250069
.

                                                            IN 90-43
                                                            June 29, 1990
                                                            Page 2 of 3


the thermal trips operated satisfactorily.  The licensee returned the MCCB 
to GE Nuclear Energy for failure and root cause analysis.  The results of 
the analysis have not yet been reported.

In May 1990, according to GPUN reports, Oyster Creek technicians 
bench-tested seven more UVR-equipped MCCBs from the same order.  Five of the 
seven failed to pass the overcurrent trip test (also at 300 percent of rated 
current) on phase C only.  In addition, GPUN reported opening one of the 
failed MCCBs, removing the UVR, and retesting the MCCB with satisfactory 
results for the thermal overcurrent trip test on phase C.  These 
experimental results suggested that the UVR had been interfering with the 
operation of the phase-C thermal overcurrent trip element because of its 
close proximity to the phase-C element.  However, it should be noted that 
the UVR is not intended to act on the thermal element, but rather on the 
common tripper bar that trips all three phases or poles.

Discussion:

On May 24, 1990, an NRC representative observed the GE ED&C testing of the 
five GE TED-type MCCBs with UVRs installed (GE catalog number 
TED136100UV4RS) which had failed pre-installation testing at Oyster Creek.  
Inspection and testing revealed that the cause of the failure of the 
overcurrent trip function was improper installation of the calibration screw 
spring clips by the Puerto Rico factory, instead of improper installation of 
the UVRs by the Knoxville facility, as previously believed by GE Nuclear 
Energy.  GE ED&C stated that the misoriented calibration screw spring clips 
have no effect on the operability of the MCCBs unless internal UVRs are 
installed.  The Oyster Creek MCCBs passed the thermal overcurrent trip tests 
at the GE Puerto Rico factory because the UVRs had not yet been installed.  
After the UVRs were installed at the GE ED&C Knoxville facility, the 
presence of the misoriented calibration screw spring clips caused mechanical 
interference between the UVR and the thermal over-current trip function.  
This was not detected at the GE ED&C Knoxville facility, because testing of 
all MCCBs normal functions was not performed.  

Deficiencies in manufacturing quality control and in the program for 
dedication of CGIs for safety-related applications were exhibited by the 
undetected misorientation of the calibration screw spring clips and the lack 
of adequate retesting following installation of the UVRs.  GE ED&C has 
indicated that action will be taken, including design changes if necessary, 
to prevent interference between the calibration screw spring clips and the 
UVRs.  In addition, GE ED&C has now instituted overcurrent trip testing of 
MCCBs following the installation of UVRs at their Knoxville facility.

Although GE ED&C's failure analysis was demonstrated by testing, it has not 
been firmly established that this condition is isolated to the MCCB shipment 
in question.  However, GE ED&C has stated that the problem is limited only 
to the thermal overcurrent trip functions on phase C of their 3-pole, 
E-frame MCCBs (types TED13XXXX and THED13XXXX), and only those equipped with 
UVRs.  This is a result of this model's unique, integral overcurrent trip 
mechanisms and the proximity of the phase C thermal trip mechanism to the 
tripping arm of an installed UVR.  

.

                                                            IN 90-43
                                                            June 29, 1990
                                                            Page 3 of 3


Oyster Creek's routine pre-installation testing procedures detected and 
prevented the use of the faulty MCCBs.  Although the MCCBs were procured as 
safety-related components through GE Nuclear Energy and were supplied with 
the vendor's 10 CFR Part 50 Appendix B quality assurance certifications, 
this testing was performed by the licensee in addition to the normal quality 
assurance receipt inspection.

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 
manager.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation


Technical Contacts:  K. R. Naidu, NRR  
                     (301) 492-0980

                     S. D. Alexander, NRR  
                     (301) 492-0995


Attachment:  List of Recently Issued NRC Information Notices

.ENDEND
Page Last Reviewed/Updated Tuesday, November 12, 2013