If receptacles are not marked as CO/ALR, what type of conductors are they suitable for use with?

When receptacles are not marked as CO/ALR, they are suitable for use with copper conductors only. The marking CO/ALR indicates that a receptacle has been specifically designed to be compatible with both copper and aluminum conductors. If a receptacle does not carry this marking, it indicates that it has not been tested or approved for use with aluminum conductors due to issues related to bonding, thermal expansion, and corrosion that may arise when connecting different metals.

Using receptacles with aluminum conductors without the appropriate markings can create significant safety hazards and reliability issues, such as overheating and increased resistance at the connection points, which can lead to fires. Therefore, it is crucial to adhere to the manufacturer's specifications and the National Electrical Code (NEC) guidelines, which clearly state that receptacles without the CO/ALR designation should only be used with copper conductors to ensure safety and performance.