What inscription on a circuit breaker indicates compatibility with both copper and aluminum wire?

The inscription that indicates a circuit breaker is compatible with both copper and aluminum wire is "AL/CU." This marking signifies that the breaker is designed to safely accommodate both types of conductors without compromising performance or safety.

When wiring installations, it is essential to ensure compatibility between the wires used and the circuit breakers in order to prevent issues such as overheating, poor connections, or potential failures. The "AL/CU" designation assures electricians and inspectors that the breaker has been tested and approved for use with both aluminum and copper conductors, thereby providing flexibility in choice of wire material based on the installation requirements or preferences.

The other options do not reflect the correct compatibility. For example, "CU/AL" suggests a different order of notation which doesn't adhere to standard labelling practices. "CU OLD" indicates something completely unrelated, and "AL ONLY" would suggest that the breaker is only suitable for aluminum wires, failing to accommodate copper, which is not the versatility needed in many wiring situations. Thus, "AL/CU" is the correct and commonly recognized marking for this type of compatibility.