Increased Copper Prices
In the mid 1960s when the price of copper spiked, aluminum wire was manufactured in sizes small enough to be used in homes. Aluminum wire requires a larger wire gauge than copper to carry the same current.
When first used in branch circuit wiring, aluminum wire was not installed any differently from copper. Typical connections from electrical wire to electrical devices, also called terminals, are usually made by wrapping the wire around screw terminals and tightening the screw. Over time, many of these terminations to aluminum wire began to fail due to improper connection techniques and dissimilar metals having different resistances and different coefficients of thermal expansion. These connection failures generated heat under electrical load and resulted in overheated connections.
In the late 1960s, a device specification known as CU/AL was created that specified standards for devices intended for use with aluminum wire. Because of more rigorous testing, larger undercut screw terminals were designed to hold the wire more suitably. Unfortunately, CU/AL switches and receptacles failed to work well enough with aluminum wire, and a new specification called CO/ALR (meaning copper-aluminum, revised) was created. These devices employ screw terminals that have even deeper undercuts and are designed to act as a similar metal to aluminum and to expand at a similar rate. CO/ALR applies only to standard light switches and receptacles; CU/AL is the standard marking for circuit breakers and larger equipment.
Read more about this topic: Aluminum Wire
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