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This is Aluminum Wiring Repair Procedure: Here Color photos and descriptive captions from CPSC Meeting 9/28/95. In this document aluminum wire twist-on connector failures and repair procedures are described, including aluminum wire repair methods which work and methods which do not work and are unsafe.
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Details of Aluminum Wiring Connector Failures: the failure mechanism, resistance, current paths, connector deterioration, inadequate standard
Equivalent circuits, general case and newly made
Color photos of aluminum wire repair procedures, and photos of failed connectors are included. This document series describes hazards with existing aluminum wiring repair products, explains the aluminum wiring failure mechanism, and reviews recommended retrofit procedures including use of readily-available materials.
This information was presented to the US Consumer Product Safety Commission by Dr. J. Aronstein, 9/28/95. The minutes of that meeting were obtained under the Freedom of Information Act and posted by Daniel Friedman January 1996.
Click any image to see an enlarged version.
20. Here are the current paths in this type of connection. Each of the paths from wire to wire has some associated resistance. The direct wire to wire path has only contact resistance, while paths
through the spring sections have contact resistance as well as bulk resistance of the steel wire.
This article continues below with an explanation of common twist on connectors and copper pigtailing as an attempt at aluminum wiring repair.
The key observation is that with this type of aluminum to copper wire splice, most of the current flows through the spring in the connector. In the design of twist-on wire connectors the purpose of the spring is to maintain tension on the spliced wires, not to conduct electricity itself.
More than 60% typically for an aluminum connection, but less than 10% for an all-copper connection. There is a basic difference in behavior with aluminum wire.
This article continues with the explanation of why twist-on connectors overheat and lead to failures when used for copper to aluminum pigtailing as an attempt at aluminum wiring repair. The observation explained here is that with this type of aluminum to copper wire splice, resistance increases between the copper and aluminum wires, leading to overheating of the connection and the twist-on the connector.
Text from attachment occurs here:
Table of UL-486C Electrical Connector Standards: comparing actual field-use with test conditions
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