ML19262A274

Nonroutine 30-Day Rept 75-01 Re 750124 Investigation Into Cause of Trip of DB-50 Feeder Breaker to 1B Es Motor Control Center.Undersized Wire Found in Unit Center.Failed Wiring Replaced W/Larger Size Wire & Change Mod Submitted

ML19262A274
Person / Time
Site:	Three Mile Island
Issue date:	02/24/1975
From:	METROPOLITAN EDISON CO.
To:
Shared Package
ML19262A272	List: ML19262A271 ML19262A274
References
75-01, 75-1, NUDOCS 7910260605
Download: ML19262A274 (1)

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Metropolitan Edisen Cenpany

'"hree Mile Island Nuclear Station, Unit 1 (T:C-1)

Docket No. 50-209 Cperating License EFE-50 Necroutine 30-Lay Repcrt 75-C1 Nctification of Apparent Eesign Leficiency

1. Descriptien of Deficiency As s result of investigations into the cause cf a trip of the EE-50 feeder breaker to the 13 IS =ctor centrol center, it was discovered en January 2h, 1975, that undersize wire existed in a unit of the center. The undersize wire served to connect the unit contained lighting panel feeder breaker to bus stabs at the rear of the unit (these bus stats , in turn, cc=plete the circuit between the subject =cter centrol center h80 V bus, and the subject lighting panel feeder breaker). As a result of this deficiency, a portion of the subject viring burned off at the lugs where the viring connects to the bus stabs, and a resulting are to grcund caused the subject DE-50 feeder breaker to trip.

Note: The events associated with the abcVe described deficiency have been reviewed, and as a result of this review it hns ceen determined that the events did not ecnstitute an abncr=al occurrence. The pri=ary reason for having made thf e deter =inatJ.cn is that the DP-50 feeder breaker to the 13 Ingineered Safeguarns Meter Centrol Center, upon tripping, was reset i=nediately (i.e. vithin about 5 seccnds).

2. Corrective Action

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Corrective acticns were taken to replace the subject fai1ed viring with larger size wire. In addition, as 1cng ter= preventative actions:

a. a change =odification has been sut=itted which lists the different size breakers fcund in the Engineered Safeguards Meter Centrcl Centers and the respective r.ini=u= size wires that need be installed between the breakers and their associated bus stabs.

b. This change modificatien is currently under review, and vill te approved by March ih, 1975

c. Folleving approval of the change =cdification, an inspecticn program vill ec=nence by April 1,1975, to inspect and replace, where necessary, under size vires with those of sufficient current carrying capability, and

d. it is presently anticipated that this prcgra= will be ec=ple. tad b7 J ne 1976.

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