Overheating Failures of Aluminum-Wired Special Service Connectors

"Special service" twist-on connectors are tested with aluminum and copper wire combinations. The special service connectors are qualified by a Canadian standard which applies to connectors for use with aluminum branch circuit conductors. Two brands of special service connectors are presently qualified by this standard and marketed. Both are rated for various combinations of aluminum and copper conductors. Samples of both brands are tested in this investigation. The tests are conducted within rated electrical and environmental conditions, with connections made according to the connector manufacturers\´ instructions. Overheating failures have occurred among the aluminum-wired special service connector combinations. The failures are accelerated by humid environment to a greater extent than by the application of electrical current. In contrast, connections which are copper-wired, using either standard or special service connectors, are stable and failure-free. The difference between the standard twist-on connectors and the special service connectors is in the material used for the connector spring. Improved compatibility between the spring material and the aluminum conductor, compared to the plated steel springs of the conventional twiston connectors, has not dealt with several important failure mechanisms. The test results indicate that the new standard, as presently defined, cannot be relied on to screen out aluminum-wired connector combinations which will not survive long-term operation within rated conditions. Thus the objective of accelerated qualification testing-- the prediction and assurance of safe and reliable operation in actual service---is not achieved in this case. The reasons are discussed, along with possible improvements