ML20079M192

Final Significant Deficiency Rept SD-49 Re Possible Cutting of Magnetic Latch Leads in 480-volt Switchgear.Initially Reported on 831214.Caused by Slack Left in Leads When Breaker Wiring Harnessed.Brown Boveri Repairs Made

ML20079M192
Person / Time
Site:	Millstone
Issue date:	01/13/1984
From:	Counsil W NORTHEAST UTILITIES
To:	Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
SD-49, NUDOCS 8401270208
Download: ML20079M192 (2)

Text

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1. (203) 666-6911 k k J .io.N EaE.nEcowasa January 13,1984 Docket No. 50-423 F003A Dr. Thomas E. Murley Regional Administrator Region I U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406

Dear Dr. Murley:

Millstone Nuclear Power Station, Unit No. 3 Reporting of Potential Significant Deficiencies in Design and Construction: 480V Switchgear (SD-49)

In a December 14,1983 telephone conversation between your Mr. W. Kinney and our Mr. T. Sullivan, Northeast Nuclear Energy Company (NNECO) reported a potential significant deficiency in the construction of Millstone Unit No. 3 as required by 10CFR50.55(e). The potential significant deficiency involves 480V Load Centers supplied by Brown Boveri Electric, Inc. which contain I-T-E solid-state trip devices to protect for overloads and faults. The trip device is an integral part of the I-T-E circuit breaker types K-6005 and K-16005 used in Millstone Unit No. 3. Testing of the type K-6005 circuit breakers revealed a problem with the cutting of the magnetic latch leads by the closing spring of the breaker. This occurred on five (5) of the one-hundred and thirty (130) total breakers of this type.

If this condition had not been detected and corrected, these circuit breakers could have been inservice without overload or fault protection. A fault on one of these unprotected breaker feeders would result in the loss of power to the whole 480V load center by tripping of the main type K-16005 circuit breaker. The breaker will operate normally with 125VDC control power to close and trip, but requires the magnetic latch circuit to automatically trip. A cut lead could go undetected until the next scheduled breaker trip testing.

The problem occurred because too much slack was lef t in the leads when the breaker wiring was harnessed. Repairs were made using the manufacturer's recommendation of splicing and use of heat shrink insulation over the splice. All breakers were inspected and wiring that had excess slack in the magnetic latch leads was tied away from the closing spring.

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The type K-1600S circuit breakers use the same magnetic latch trip feature,-

however, the physical mounting is different and the leads are not close to the closing spring. Hence, this did not result in a similar problem e> perienced by the type K-6005 circuit breakers.

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. This letter constitutes our final report closing out all items related to SD-49.

Ve trust that the above information satisfactorily responds to your concerns.

Very truly yours, W. G. Counsil Senior Vice President cc: Mr. R. C. DeYoung, Director Division of Inspection and Enforcement U. S. Nuclear Regulatory Commission Phillips Building 7920 Norfolk Avenue Bethesda, MD 20014

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