Bulletin 78-06: Defective Cutler-Hammer, Type M Relays with DC Coils
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
May 31, 1978
IE Bulletin No. 78-06
DEFECTIVE CUTLER-HAMMER, TYPE M RELAYS WITH DC COILS
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
permit:
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).
1 of 2
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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
problems.
Attachments:
Cutler-Hammer Notification
2 of 2
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MAILGRAM
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.
NOTIFICATION OF POTENTIAL PRODUCT 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
terminals.
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
Attachment
IE Bulletin 78-06
Page Last Reviewed/Updated Tuesday, March 09, 2021