REG NASA-LLIS-1229-1998 Lessons Learned - High electrical resistance from loose connectors.pdf

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1、Lessons Learned Entry: 1229Lesson Info:a71 Lesson Number: 1229a71 Lesson Date: 1998-12-10a71 Submitting Organization: JSCa71 Submitted by: Dan Gaudenti/ Ronald A. MontagueSubject: High electrical resistance from loose connectors Description of Driving Event: While performing electrical checkout of a

2、 newly manufactured electronic component, erratic high-current measurements were noticed. Some technicians in the area believed they also occasionally smelled something burning. While a drawer was removed for other troubleshooting, it was noticed that the wires connected to a contactor were loose. A

3、fter removing the contactor cover, overheating of the lugged wires and nut/bolt connection was obvious; there was discoloration typical of high temperatures. The contactor cover was also slightly melted and burned. This high-resistance connection caused overheating when large currents were flowing.

4、The wire lugs were welded to the bolt and the nut could not be removed (or tightened). The contactor had to be replaced and the wires re-lugged. Root cause: Nut tightness check was missed during in-process assembly inspection. The company that assembled the console did not tighten the contactor wire

5、s. The nut was spun on to the bolt, but it was not even finger tight.Lesson(s) Learned: Extreme care must be given to unplanned disconnection of previously connected electrical contactors to ensure that a good connection is restoredRecommendation(s): After applying final assembly torque, consider ap

6、plying to all critical connections “Torque Stripe“ paint that spans the joint between the nut and the adjacent connector surfaces. Then visual inspection of the “Torque Paint“ will verify final assembly of the critical joints. Subsequent loosening or removal of the nut will be detectable due to the

7、crack in the paint that will result at the joint. If joint is loosened, tag the loosened joint and perhaps remove “Torque Paint“. Apply new “Torque Paint“ when joint is fully reassembled. All high-power connections must be thoroughly checked before Provided by IHSNot for ResaleNo reproduction or net

8、working permitted without license from IHS-,-,-initially applying power. The Power/Control Drawer was given a visual inspection before use, however the loose connections were not visible beneath the contactor cover. It should not be assumed that a company experienced with electrical assembly has pro

9、perly checked all connections. Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Configuration Managementa71 Energya71 Flight Equipmenta71 Ground Equipmenta71 Hardwarea71 Industrial Operationsa71 Parts Materials

10、& Processesa71 Policy & Planninga71 Safety & Mission AssuranceAdditional Info: Approval Info: a71 Approval Date: 2002-06-27a71 Approval Name: Ronald A. Montaguea71 Approval Organization: JSCa71 Approval Phone Number: 281-483-8576Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-