The greater coefficient of thermal expansion of aluminium causes the wire to expand and contract relative to the dissimilar metal screw connection, eventually loosening the connection.
Pure aluminium has a tendency to creep under steady sustained pressure (to a greater degree as the temperature rises), again loosening the connection.
Galvanic corrosion from the dissimilar metals increases the electrical resistance of the connection.
All of this resulted in overheated and loose connections, and this in turn resulted in some fires. Builders then became wary of using the wire, and many jurisdictions outlawed its use in very small sizes, in new construction. Yet newer fixtures eventually were introduced with connections designed to avoid loosening and overheating. At first they were marked "Al/Cu", but they now bear a "CO/ALR" coding.
Another way to forestall the heating problem is to crimp the aluminium wire to a short "pigtail" of copper wire. A properly done high-pressure crimp by the proper tool is tight enough to reduce any thermal expansion of the aluminium. Today, new alloys, designs, and methods are used for aluminium wiring in combination with aluminium terminations.
Guangdong Shunde Seko Machinery & Technology Co.,Ltd.www.gdseko.com
Lucy Xie
sevvice@gdseko.com
Skype:Lucy
Xie,SEKO Machinery
Skype:Lucy
Xie,SEKO Machinery
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