What is the marking for receptacles and switches designed for both copper and aluminum wires rated at 15 or 20 amps?

The marking for receptacles and switches that are designed to be compatible with both copper (CU) and aluminum (AL) wires, specifically those rated at 15 or 20 amps, is CO/ALR. This designation indicates that the device has been tested and is safe for use with aluminum wire, which can have different properties when compared to copper. The "R" signifies that the device is rated for aluminum wire applications, ensuring that the connection remains secure and minimizes the risk of overheating or connection failure.

This marking is crucial because aluminum wire has a tendency to expand and contract more than copper when heated, leading to potential loosening of connections. Therefore, devices marked CO/ALR incorporate specific design features to accommodate this characteristic and ensure reliability and safety in electrical installations. Understanding these markings is important for anyone working with electrical systems, particularly in contexts where both types of wiring might be present.