United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9609050007

                                                        GE Nuclear Energy

                                   General Electric Company
                                   175 Cutner Avenue, San Jose, CA 95125

August 30, 1996
MFN 146-96

Document Control Desk
United States Nuclear Regulatory Commission
Washington, DC 20555

Subject:  GE Type RMS-9 Overcurrent Trip Device Programmers with
          Instantaneous Trip Function

This letter provides the results of an evaluation by GE Nuclear Energy
(GE-NE) of failures reported in the Instantaneous Trip Function of GE
Type RMS-9 Overcurrent Trip Device Programmers.  These devices were
manufactured by GE Electrical Distribution and Control, and supplied by
GE-NE as Safety Related components for balance-of-plant or unspecified
applications.  Since the specific applications and associated safety
functions of the RMS-9 Programmers are not known to GE-NE, we transferred
information to the affected licensees pursuant to 10 CFR Part 21.21(b).
However, since additional licensees may have purchased these devices from
other dedicating entities, we cannot assure ourselves that all end-users
have been notified.  We are therefore providing the results of our
evaluation to the NRC for appropriate action.


A domestic BWR licensee has reported to GE Nuclear Energy (GE-NE) that a
number of GE Type RMS-9 Overcurrent Trip Device Programmers were failing
to operate as expected.  The Instantaneous Trip Function was tripping the
circuit breaker at values less than the RMS-9 Programmer switch setting
would have implied.

The licensee sent three (3) of these RMS-9 Programmers to GE-NE for
testing, evaluation, and failure analysis.  Subsequent testing confirmed
that the Instantaneous Pickup Switches sometimes failed to their lowest
value (1.5X).  At other times, changing the switch setting had no
apparent effect on the RMS-9 Programmer setting.  Only the Instantaneous
Pickup Switch appears to be affected.  GE-NE has not identified any
problem with the other switches on the RMS-9 Programmers.

GE-NE has determined the cause of the problem with the Instantaneous
Pickup Switch to be a polyester epoxy film on the internal switch
contacts.  This film acts as an insulator and consequently, when the
switch position is changed, the contacts are prevented from making full
contact and the RMS-9 Programmer fails

to its lowest Instantaneous Pickup setting (1.5X).  This film is
apparently the result of insufficient curing of the conformal coating
(polyester epoxy) applied to the RMS-9 Programmer during final assembly.
Testing has shown that some of the conformal coating ran under the switch

when it was applied and was not cured because it was shadowed by the
switch during the ultraviolet curing process.  Over a period of time the
external contacts of the switch acted as wicks and drew some of the
uncured conformal coating into the switch where it then formed the film
on the internal switch contacts.  Since the thickness of the film on the
internal contacts varies, the effect is to cause the switch to fail to
it's lowest setting.  At this setting the film is thick enough to act as
an open circuit and to cause the switch to operate erratically.

While this same action may have occurred at other switches in the RMS-9
Programmer, the higher current through the switches allowed the film to
"burn off".  This is why only the Instantaneous Pickup Switch is being

Based on the testing performed by GE-NE the film does not appear to form
between the movable contacts and the stationary contacts in the switch.
This means that if the switch is operating properly and is not moved from
the position verified to have proper operation, the switch will continue
to operate properly.

The affected RMS-9 Overcurrent Trip Device Programmers were manufactured
by GE Electrical Distribution and Control, and supplied by GE-NE as
Safety Related components for balance-of-plant or unspecified
applications.  They were variously provided as spare parts or as
components of either refurbished circuit breakers or new AK7/AKR7 circuit

An RMS-9 Programmer with the Instantaneous Pickup Function failed to it's
lowest value or at some value lower than anticipated could result in the
inability to start a motor due to the starting current of the motor being
above the Instantaneous Pickup setpoint of the RMS-9 Programmer.
Likewise, if the Instantaneous Pickup setpoint is at some value higher
than expected, it is possible that a circuit fault could result in the
circuit breaker not tripping in accordance with the selective tripping
scheme of the power system.  This could result in losing significant
portions of the power system due to the circuit breaker failing to trip
when expected and thus forcing upstream circuit breakers to isolate a

GE-NE recommends that as the final step in any procedure requiring the
repositioning of the Instantaneous Pickup Switch, the proper operation of
the Instantaneous Trip Function be verified by testing.  This testing may
be performed by Primary Current Injection or by using the GE TVRMS Test
Set to verify the "electronic" position of the Instantaneous Pickup
Switch.  This recommendation is based on the evidence that a properly
operating switch will continue to operate properly unless and until the
switch position is changed such that the film (if present) comes into


If you have any questions, please call me at (408) 925-1019.


Michael A. Smith, Manager
Safety Evaluations Project

cc:  G. C. Cwalina (NRC-NRR/DOTS/TSIB)
     J. M. Austin (GE-NE)
     C. R. Flanigan (GE-NE)
     D. Fletcher (GE ED&C/Plainville)
     H. J. Neems (GE-NE)
     N. C. Shirley (GE-NE)
     PRC File



Page Last Reviewed/Updated Wednesday, February 12, 2020