United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-05: Potential Coil Insulation Breakdown in ABB RXMH2 Relays

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                               January 8, 1992

                               IN ABB RXMH2 RELAYS


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 
involving the coil insulation breakdown in Asea Brown Boveri (ABB) RXMH2 
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 August 12, 1991, United Controls Division of Hub, Incorporated, (United 
Controls) notified the NRC in accordance with Part 21 of Title 10 of the 
Code of Federal Regulations (10 CFR Part 21) concerning the failure of an 
ABB RXMH2 relay being used in the emergency diesel generator (EDG) bus load 
sequencing panels at the Florida Power & Light Company's Turkey Point 
Generating Station.  The failed relay, one of approximately 300 ABB relays 
installed at Turkey Point, had failed to change state upon being energized 
during a preoperational test.  United Controls purchased the relay from ABB 
as a commercial grade item and dedicated the relay for safety-related use as 
part of Turkey Point's EDG sequencing panels.  On August 16, 1991, ABB also 
notified the NRC in accordance with 10 CFR Part 21 and provided further 
information concerning the failed relay.


ABB conducted a failure analysis and found that the coil in the relay had 
suffered a short circuit of the windings at the point at which the beginning 
lead of the coil was crossed by the subsequent windings of each layer of 
wire as they were wound onto the coil spool.  The beginning lead and the 
subsequent windings were to be separated by a piece of clear plastic 
adhesive tape placed over the beginning lead to hold it in a channel in the 
end flange of the coil spool.  The separation tape would then hold the 
beginning lead in place and prevent abrasion from the subsequent windings 
during the winding process.  However, upon examining the failed coil, ABB 
determined that during the winding 


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                                                            January 8, 1992
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process, the tape had been pulled back and dislocated away from the 
beginning lead it was supposed to hold in the end flange channel of the coil 
spool.  Some of the varnish insulation on the beginning lead was then 
apparently abraded during the winding process, allowing the insulation 
breakdown which caused the relay to fail.  

ABB inspected other relays, none of which had yet failed, to determine if 
the separation tape was adequately placed.  The acceptance criterion 
established by ABB specified that the separation tape must cover the 
beginning lead with an overlap margin of 1.0 millimeter (mm) or greater.  
Although none of the relays had damaged or dislocated separation tape, ABB 
found that almost all of them had less than 1.0 mm of margin.  

United Controls and ABB determined that the problem had generic implications 
but that the scope was limited to relays with the particular coil design in 
question (type RXMH2, Models RK223068-EA and RK223069-EA) manufactured from 
March 1989 through September 1990.  ABB identified the root cause of the 
problem as the performance of one factory employee who had manufactured 
relays within the date codes cited above.  

ABB has made a design change to reposition the separation tape on the end 
flange of the coil spool to more evenly cover the beginning lead and avoid 
conditions that could cause the separation tape to be dislocated during the 
winding process. ABB has also taken action to ensure that all pertinent 
draw-ings and procedures have been updated and corrected and that all 
affected employees have been trained on the changes. 

The manufacturer, ABB, did not believe that field data indicated a 
reliability problem with the type RXMH2 relay but recommended that in 
applications in which a failure to operate could cause a substantial safety 
hazard, the relays be checked for coil insulation integrity.

The RXMH2 relays having the potential for insulation breakdown were manufac-
tured from March 1989 to September 1990.  The relays are marked in the upper 
right corner of the legend plate with the year and week of manufacture; the 
dates of concern indicated as 8909 up to, and including, 9036. 

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:  Bill Rogers, NRR
                    (301) 504-2986

1.  ABB 10 CFR Part 21 Notification to the NRC
2.  List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015