United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-06: Defective Cutler-Hammer, Type M Relays with DC Coils

                               UNITED STATES 
                          WASHINGTON, D. C. 20555 
                               May 31, 1978  

                                                     IE Bulletin No. 78-06 


Description of Circumstances: 

The Duke Power Company recently reported that during a series of tests of 
the Emergency Power Switching Logic System at Oconee Nuclear Station, four 
relays in the standby buses #1 and #2 voltage sensing circuitry were found 
to be inoperable. The relays are identified as Cutler-Hammer Type M, DC 
Relays, Catalog No. D23 MRD. This finding prompted the licensee to perform 
another test of the Emergency Power Switching Logic during which one 
additional relay of the same type and model as identified above also failed. 
To date, twelve failures of this DC relay type have occurred at Oconee 
Nuclear Station. 

The manufacturer determined that cause for failure was loss of arc gap in 
the coil clearing contact where the normal mode of operation is to have the 
coil continuously energized. The purpose of this contact is to interrupt the
inrush current to the pickup coil winding in order to prevent winding burn 
out. The loss of arc gap in the clearing contact was caused by an abnormal 
amount of heat induced shrinkage of molded magnet carriers which are used in
subject relays manufactured between 1971 and July of 1976. According to 
Cutler-Hammer, the loss of arc gap affects the performance of only the type 
M relays with DC coils since relays with AC coils do not use the coil 
clearing contact feature. 

The attached Cutler-Hammer Notification Of Potential Product Failure was 
sent to all distributors of type M relays with DC coils with instructions to
notify end users of the potential problems. The notification identifies the 
problem and provides their recommended corrective action. 

Action To Be Taken By Licensee: 

For all power reactor facilities with an operating license or construction 

1.   Determine whether Cutler-Hammer Type M Relays with a DC coil are used 
     or planned to be used in safety-related systems at your facility(ies). 

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IE Bulletin No. 78-06                                        May 31, 1978 

2.   If such relays are used or planned for use in safety-related systems 
     describe what corrective actions you have taken or plan to take to 
     assure proper relay operation. 

3.   Facilities having an operating license should report in writing within 
     45 days and facilities with construction permits within 60 days, the 
     results of action taken or planned with regard to Items 1 and 2 above. 
     Your written reply should also include the date when such actions were 
     or will be completed. 

Reports should be submitted to the Director of the appropriate NRC Regional 
Office and a copy should be forwarded to the U. S. Nuclear Regulatory 
Commission, Office of Inspection and Enforcement, Division of Reactor 
Operations Inspection, Washington D.C. 20555. 

Approval by GAO, B180225 (R0072); clearance expires 7/31/80. Approval was 
given under a blanket clearance specifically for identified generic 

Cutler-Hammer Notification

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You may have purchased for resale, some of the type M relays with d-c coils 
described below. If you have, please take action to notify your customers of
a potential mode of failure. 


Some Cutler-Hammer type M relays with d-c coils produced from 1971 thru July
of 1976, that are used in circuits where the normal mode of operation is to 
have the coil continuously energized, may eventually fail due to loss of arc
gap in the coil clearing pole.  This loss of arc gap is primarily caused by 
an abnormal amount of heat-induced shrinkage in some of the molded magnet 
carriers. If the relay is used in this circuit where the coil is 
continuously energized, the heat from the coil may cause the magnet carrier 
to shrink to a point where the arc gap in the coil clearing pole becomes too 
small to break the inrush current of the pickup coil winding, causing the 
coil to overheat and burn out. In some cases, the damage from the coil 
burning out may result in the relay being stuck in the ON (energized) 
position, thus preventing it from dropping out when power is removed from 
the coil. 

If you are aware of any applications where this relay is used in a 
continuously energized mode and where a failure as described above may 
result in a hazard, have that relay removed and replace it with a current 
Cutler-Hamer D26MRD type M d-c relay. 

Cutler-Hamer type M relays can be identified by the front nameplate, and 
those with d-c coils can be further identified by looking for the wire from 
pickup winding of the coil that connects to the coil clearing pole. This 
wire protrudes from the coil molding on the opposite side as the normal coil

The date code indicating when the relay was produced is stamped in white ink
on the lower deck molding either in the center just above the coil terminals
or on the leg of the lower deck molding adjacent to the coil terminals. The 
date code consists of either the month and year (example 6-75) or the month 
and year followed by an inspector number which may be 2 or 4 digits (example
12717121 which is December 1971). 

If you need additional information, please contact the writer at Area Code 
414 442-7800, Ext. 2458. 

                                        John H. Breunig 
                                        Product Marketing Engineer 
                                        Logic Device Marketing 
                                        Cutler-Hammer Inc.
                                        Milwaukee, Wisconsin 53216

                                                          IE Bulletin 78-06
Page Last Reviewed/Updated Friday, July 10, 2020