United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-85: Problems with the Latching Mechanism in Potter and Brumfield R10-E3286-2 Relays

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

                               December 21, 1994


NRC INFORMATION NOTICE 94-85:  PROBLEMS WITH THE LATCHING MECHANISM IN
                               POTTER AND BRUMFIELD R10-E3286-2 RELAYS


Addressees

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

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to problems reported by C&D Charter Power Systems
(C&D) in the latching mechanism of Potter and Brumfield R10-E3286-2 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

On September 7, 1994, in accordance with Title 10 of the Code of Federal
Regulations, Part 21, C&D reported a defect in the latching mechanism of some
Potter and Brumfield R10-E3286-2 relays that were supplied by C&D to nuclear
power plants.  The relays are part of a C&D High Voltage Shut Down Alarm
Assembly Printed Circuit Board (MBC-2920-E) and may be used in Class 1E
safety-related C&D ARR Battery Chargers.  C&D reported that the defect allows
the relay to change state and cause an apparent high voltage shutdown of the
battery charger terminating charging of the battery system until the relay is
reset.  Over a period of time, this would allow the batteries to become
discharged if the relay is not reset.

C&D reported finding the defect in date code lots 9108 and 9242.  These date
codes indicate that lot 9108 was manufactured in February 1991 and lot 9242
was manufactured in October 1992.  The date codes are located on the front of
the relays.  However, other code lots may be similarly affected.

Discussion

The relays discussed above are part of the C&D MBC-2920-E printed circuit
board installed in C&D ARR Battery Chargers.  C&D reported that the problem
relays are susceptible to inadvertent changes in the state of the
normally-open and normally-closed contacts.  The cause of the problem appears
to be a push-to-release push-button on the relay that may move outward, under
shock or vibration, from the case of the relay allowing the contacts to

9412150181.                                                             IN 94-85
                                                             December 21, 1994
                                                             Page 2 of 3 


change state and latch in an unwanted state.  The relay must then be manually
reset by pushing the push-button to release the latching mechanism and return
the relay to its normal state. 

C&D indicated that they have been successful in detecting problem relays by
manually pulling the relay reset push-button out and away from the case of the
relay.  According to C&D, if the push-button can be pulled out and away from
the case of the relay by manually pulling on the push-button or twisting and
rotating the push-button while pulling on it, then the relay is likely to be
susceptible to an inadvertent change of state as described above. 

C&D purchased the suspect lots of R10-E3286-2 relays as commercial grade and
dedicated them for use on MBC-2920-E circuit boards.  C&D supplied NRC with a
list of utilities and one non-utility to which C&D had sold battery chargers
or replacement circuit boards since February 1991 and which may have
R10-E3286-2 relays from date code lots 9108 and 9242.  The list included: 
Browns Ferry; Chin Shan (Taiwan); Cooper; Farley; Grand Gulf; Hatch; Kuosheng
(Taiwan); Laguna Verde (Mexico); Limerick; Maanshan (Taiwan); Salem; San
Onofre; Vermont Yankee; Vogtle; Waterford 3; and MKW Power Systems, Inc.
(nonutility).  MKW Power Systems, Inc. may have sold these circuit boards to
nuclear utilities.  

C&D reported that C&D intends to inform the above purchasers of the problem
and advise them to check for defective relays on the MBC-2920-E circuit boards
in use or in stock.  C&D indicated that circuit boards with suspect relays may
be returned to C&D for testing and repair or replacement.  

The two relay code lots reported by C&D may not be the only code lots of
Potter and Brumfield R10-E3286-2 relays (formerly sold commercially by Potter
and Brumfield as R10H/R10K series relays) that are affected.  At the  present
time, the NRC has only been informed that the suspect relays have been
installed in MBC-2920-E circuit boards for use in C&D ARR Battery Chargers. 
However, the relays may have been supplied to nuclear facilities for other
uses.  Because other code lots may be affected and because the R10-E3286-2
relay may have been sold as commercial grade and subsequently dedicated for
safety-related use, it is important for licensees to be aware of the potential
for these relays to inadvertently change state and latch in an unwanted
position.
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                                                             December 21, 1994
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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
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.


                                    /s/'d by B.D. Liaw /for/

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

Technical contacts:  Virgil L. Beaston, NRR
                     (301) 504-2989

                     Bill H. Rogers, NRR
                     (301) 504-2945

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