United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-03: Remote Trip Function Failures in General Electric F-Frame Molded-Case Circuit Breakers

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                               January 6, 1992

                               ELECTRIC F-FRAME MOLDED-CASE CIRCUIT 


All holders of operating licenses or construction permits for nuclear power 


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees to a potentially safety-significant problem 
resulting from the possible failure of the remote trip functions of General 
Electric (GE) F-frame (225-ampere frame size) molded-case circuit breakers 
(MCCBs).  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 are not NRC requirements; therefore, no specific action or written 
response is required.

Description of Circumstances

On November 5, 1991, GE Nuclear Energy (GE NE), San Jose, California, issued 
an interim notification of its evaluation of a deviation in accordance with 
the latest revision (effective October 29, 1991) of Part 21, "Reporting of 
Defects and Noncompliance," of Title 10 of the Code of Federal Regulations 
(10 CFR Part 21).  The notification described the deviation as a "tolerance 
buildup" in certain GE F-frame MCCBs with undervoltage releases (UVRs) and 
shunt trip devices (STs) that may inhibit these internal accessory remote 
trip devices from functioning properly under conditions that produce 
sustained high internal temperatures in the MCCBs.

The attachment to the GE NE notification was taken from a draft Service 
Advice Letter (SAL) on this subject being prepared by the MCCB manufacturer, 
GE Electrical Distribution and Control (ED&C), in Plainville, Connecticut.  
GE NE plans to send the 10 CFR Part 21 interim notification to all of its 
customers who have purchased F-frame MCCBs for safety-related applications 
and to all GE NE Material Services field representatives.  GE ED&C plans to 
send the SAL (issued November 25, 1991 as SAL 91-2F) to all of its customers 
of record, many of whom are distributors.  However, both the F-frame MCCBs 
and their accessory trip devices are available on the open market as 
commercial grade items through various distribution paths.  Therefore, the 
licensees for some nuclear plants who use these MCCBs may not receive the GE 


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Although still evaluating the problem, the MCCB manufacturer has determined 
that assembly and operational variations caused the reported failures.  The 
variations reportedly resulted from (1) tolerances in mounting the accessory 
trip devices in the MCCBs, (2) tolerances on the adjustment of the ambient 
compensating bimetal (part of the thermal overload trip mechanism), and (3) 
sustained high operating temperatures in the MCCBs.  The high internal 
temperature in the MCCB required to produce a condition conducive to the 
malfunction can result from continuous high current load (greater than 50 
percent of the overcurrent trip unit rating for more than 2 hours) together 
with a high ambient temperature in the enclosure.  A secondary heat source 
could also produce the high temperatures required for this malfunction.

GE NE stated in its interim notification that UVR- and ST-equipped MCCBs 
produced after April 1991 (date codes J116= and I116=) incorporated changes 
that would prevent this condition.  GE NE also stated that an MCCB may or 
may not exhibit this malfunction, depending on the particular circumstances 
associated with the assembly of the breaker and the accessory remote trip 
devices, in conjunction with the high temperature service conditions 
believed to be conducive to failure.  Nevertheless, GE NE maintained that 
affected MCCBs will trip under overcurrent conditions and will trip remotely 
at the lower MCCB internal temperatures usually present with lower load 
currents and enclosure ambient temperatures or without secondary heat 

GE NE initially reported that it had identified a specific safety-related 
application for the affected F-frame MCCBs equipped with internal accessory 
remote trip devices.  The identified application is associated with the 
multiple electrical protection assemblies (EPAs) used in boiling water 
reactor (BWR) plants to monitor power quality to the reactor protection 
system (RPS).  The EPAs trip the F-frame breakers for the RPS power supplies 
by means of the remote trip devices if the EPAs detect overvoltage, 
undervoltage, or underfrequency conditions in RPS power.  In addition, GE NE 
informed the NRC in a subsequent communication that it may also have 
supplied some of the affected MCCBs as part of subassembly-level 
applications not separately identified in GE NE records.  The affected MCCBs 
fitted with factory-installed remote trip accessories may also be used in 
numerous other applications in all types of nuclear plants in which remote 
tripping of an F-frame MCCB by means of the UVR or ST may be a 
safety-related function.

The presence of UVRs or STs in F-frame MCCBs should be apparent when the 
units are installed in the plant.  However, even if accessory designation 
markings are not evident, affected MCCBs can be recognized by the two UVR or 
ST lead wires protruding through small openings in the sides of the MCCB 
case.  Additionally, UVRs set up for monitoring 240, 480, or 600 volts-AC or 
250 volts-DC should have an external dropping resistor connected in series 
with one of their lead wires.  Attachment 1 lists the breaker frame type 
designations of 


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                                                         Page 3 of 3

the potentially affected MCCBs and the catalog numbers of the affected 
internal accessory remote trip devices and also gives the date codes of the 
units believed by the manufacturer to be affected.

In view of the potentially wide scope of application of the affected MCCBs, 
addressees may find the affected types of UVR- and ST-equipped MCCBs both 
installed and in the warehouse.  Addressees who find any affected MCCBs may 
consult the manufacturer on this subject to determine the appropriate 
corrective action, including testing for the existence of the malfunction, 
analyzing the potential high temperature producing conditions, or replacing 
the affected components.

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
the technical contact listed below or the appropriate Office of Nuclear 
Reactor Regulation (NRR) project manager. 

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

Technical contact:  S. D. Alexander, NRR
                    (301) 504-2995

1.   Affected MCCBs and Accessories
2.   List of Recently Issued NRC Information Notices


                                                         Attachment 1
                                                         IN 92-03
                                                         January 6, 1992
                                                         Page 1 of 1

                       AFFECTED MCCBs and ACCESSORIES

The affected GE F-frame ("F-225 Line") MCCBs include the breaker types or 
frames listed below which can be fitted with any of the accessory remote 
trip devices with the listed catalog numbers:


TFK, THFK                     TFKSTA12                      TFKUVA1
TFJ                           TFKSTA13                      TFKUVA2
THLC2                         TFKSTA7                       TFKUVA4
THLB2                         TFKSTA8                       TFKUVA6
THLC4                         TFKSTA9                       TFKUVA7
TLB4                          TFKSTA11                      TFKUVA8

According to GE NE and GE ED&C, the tolerance buildup affects F-frame MCCBs 
and UVRs and STs assembled between August 1979 and April 1991 (accessory 
date codes N927* through N116=).  The potentially affected MCCBs could have 
manufacturing date codes J927* through J116= (I116= for current limiting 
frames), but ED&C reported no identifiable volume of field returns for this 
condition among MCCBs built before the fourth quarter of 1987 (breaker date 
codes J736+ and I736+).  The accessory date code is its manufacturing date 
code and only appears on the accessory itself.  However, the date code from 
the accessory installation facility may appear on the MCCB case in addition 
to the manufacturing date code of the MCCB. 

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