United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 96-62: Potential Failure of the Instantaneous Trip Function of General Electric RMS-9 Programmers

                                 UNITED STATES
                        NUCLEAR REGULATORY COMMISSION 
                     OFFICE OF NUCLEAR REACTOR REGULATION
                         WASHINGTON, D.C.  20555-0001

                               November 20, 1996


NRC INFORMATION NOTICE 96-62:  POTENTIAL FAILURE OF THE INSTANTANEOUS TRIP     
                               FUNCTION OF GENERAL ELECTRIC RMS-9 PROGRAMMERS


Addressees

All holders of operating licenses and construction permits for nuclear power
plants.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential that the instantaneous trip
function of some General Electric RMS-9 overcurrent trip device programmers
may fail to trip the associated 480-V ac circuit breaker at the desired
current setting.  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

General Electric Nuclear Energy (GE NE) sent the results of an evaluation of
some reported failures of the instantaneous trip function of GE Type RMS-9
Overcurrent Trip Device Programmers to all affected customers and the NRC in a
letter dated August 30, 1996.  These devices were provided as spare parts, or
as components of either refurbished GE Type AK 480-V ac circuit breakers or
new AK7/AKR-7 circuit breakers for overcurrent protection.  The affected
programmers may trip at an instantaneous current value below the selected
setting.

The devices were manufactured by GE Electrical Distribution and Control and
supplied by  GE NE as safety-related components for balance-of-plant and
unspecified applications.  Since the specific applications and associated
safety functions of the RMS-9 programmers are not known to GE NE, the company
notified affected licensees in accordance with  10 CFR 21.21(b).  However,
because some licensees may have purchased these devices as commercial-grade
items or from a dedicating entity other than GE NE, the NRC is issuing this
information notice to ensure that all potentially affected licensees are
notified.


9611040290.                                                            IN 96-62
                                                            November 20, 1996
                                                            Page 2 of 3


Discussion

The cause of the failure of the instantaneous trip function was determined to
be a polyester epoxy film on the internal switch contacts.  The film acts as
an insulator, so that if the instantaneous switch setting is changed from its
initial setting, the contacts do not 
make and the programmer automatically fails to its lowest instantaneous pickup
setting (1.5X).  The film is the result of insufficient curing of the
conformal coating (polyester epoxy) applied to the RMS-9 programmer during
final assembly.  Testing by GE showed that some of the coating ran under the
switch during application and the coating was not properly cured because it
was masked by the switch during the ultraviolet curing process.  Over time,
the external switch contacts acted as wicks and drew some of the uncured
coating into the switch where it formed a thin film on the internal switch
contacts.

Testing by GE also showed that the film did not form between the movable
contacts and the stationary contacts in the switch.  Therefore, if the
instantaneous trip function is operating properly and the switch has not been
moved from its initial position, it should continue to operate properly.

An RMS-9 programmer that trips at a value lower than the selected value could
cause a motor to fail to start because the starting current could be higher
than the setpoint in the programmer.  If a programmer trips at higher than
expected value, it is possible that the breaker may not trip soon enough under
fault conditions and other breakers upstream may have to trip to clear the
fault, resulting in the loss of more of the power system than anticipated. 
However, no reported failures of the type discussed herein have resulted in a
breaker tripping at a current higher than the desired setting.

Related Generic Communications

NRC Information Notice 93-75, "Spurious Tripping of Low-Voltage Power Circuit
Breakers With GE RMS-9 Digital Trip Units," was issued on September 17, 1993,
to alert licensees to the potential for the RMS-9 programmers to cause
spurious circuit breaker trips when exposed to short duration (100
microseconds) current spikes (high-frequency electrical noise).  Although the
same component is involved in both instances, the two problems are unrelated.

.                                                            IN 96-62
                                                            November 20, 1996
                                                            Page 3 of 3


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 Office of
Nuclear Reactor Regulation (NRR) project manager.




                                    Thomas T. Martin, Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical contacts:  Stephen D. Alexander, NRR
                     (301) 415-2995             
                     E-mail: sda@nrc.gov

                     David L. Skeen, NRR
                     (301) 415-1174
                     E-mail: dls@nrc.gov


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