United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-41: Problems with General Electric Type CR124 Overload Relay Ambient Compensation


June 7, 1994



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 the potential for out-of-tolerance ambient
compensation in certain configurations of General Electric (GE) Type CR124
overload relays.  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

After some field test failures, in which several Type CR124 overload relays
exhibited out-of-tolerance trip times, the relays were returned to the
manufacturer, GE Electrical Distribution and Control (ED&C).  GE ED&C
discovered that on relay models CR124K028, K128, L028, and L128, manufactured
before October 1990, many of the ambient temperature-compensating bimetal
elements (sometimes called ambient compensating springs) had been installed
upside down because of a problem with the marking of the elements.  In this
condition, the incorrectly installed element can adversely affect the trip
timing of the relay.  These overload relays are typically used in conjunction
with starters or motor controllers, many of which may serve safety-related
loads.  In April 1991, GE Nuclear Energy (GE NE) issued a "Germane to Safety"
letter to all boiling water reactor customers and certain other customers
concerning the relays.  However, the NRC has learned that other licensees may
also be affected.


The ambient temperature compensating bimetal element or spring is intended to
adjust the trip forces inside the relay so that the trip time as a function of
overload current is consistent with the design characteristic curves over a
wide range of ambient temperatures.  According to GE, the improperly installed
ambient compensating bimetals will permit the overload relays to work
correctly within a temperature range of 15-20C [59-68F].  However, at lower
temperatures, i.e., 0-15C [32-59F], the ambient compensation would cause

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trip times above published specifications (time-current curves).  At higher
temperatures, i.e., 20-40C [68-104F], which is more typical of nuclear plant
installations, the ambient compensations would cause trip times below
published specifications.  GE ED&C did not have data on the magnitude of
deviations from the published time-current curves.

GE NE indicated that the above identified models made before October 1990 may
be affected by this problem.  To identify when the relays were built, they are
marked with date codes consisting of two letters.  The first letter, "N"
through "Z" (skipping "Q"), indicates month of manufacture.  The second letter
indicates the year with "D" meaning 1989, "E" meaning 1990, etc.  Hence relays
of the affected models built before October 1990, i.e., in September 1990 and
earlier (date codes "WE" and earlier), are affected.  ED&C has issued no
service advice letters (SALs), nor has GE NE issued any service information
letters (SILs), on this issue.  Since late 1991, ED&C has used 5-character,
alphanumeric, in lieu of 2-letter date codes for the relays and similar

Because the affected relays are reported to work properly within the
temperature range of 15-20C [59-68F], ED&C recommended evaluating individual
applications in terms of actual service conditions and performance
requirements to determine the potential impact on operability of the overload
relays with defective ambient compensation.  In addition, because some of the
potentially affected relays may not be defective, GE ED&C provided a test
procedure that may be used as an alternative to wholesale replacement to
identify those relays that actually have the improperly installed ambient
compensation bimetal.  The procedure is to test the relays at a nominal
overload current (e.g., 300 percent) at room temperature (e.g., 25C [77F])
and then repeating the test after thermal soaking at 40C [104F] and
verifying that the cool and warm trip times at the same overload level are
within 10 percent of each other.  If these relays fail this test and the
condition cannot be tolerated because of requirements of the application, ED&C
stated that these relays would need to be replaced because they cannot be
repaired.  ED&C also recommended the test procedure described above for
general use on ambient compensated thermal overload relays, installed or in
storage, which ED&C recommended testing at least every five years.
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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.

                                      original signed by

Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation

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

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