Where a switch is marked "CO/ALR," it is suitable for use with which of the following types of conductors?

The marking "CO/ALR" on a switch indicates that it is rated for use with copper conductors (CO) and aluminum conductors (ALR). This is significant because it assures users that the switch can safely handle the thermal and electrical properties of these types of wiring without risk of overheating or failure.

When a switch is marked as suitable for both copper and aluminum conductors, it indicates that the materials and construction of the switch are designed to accommodate the different expansion rates and conductivity characteristics of these metals. It is particularly important when aluminum is involved, as it requires special considerations to ensure safe and reliable connections.

The inclusion of "CO/ALR" suggests that the switch can also be compatible with copper-clad aluminum conductors, which contain a layer of copper surrounding an aluminum core. This type of conductor combines benefits of both copper and aluminum, but inherently requires products designed for both materials.

Therefore, the correct answer encompasses all three types of conductors: copper, aluminum, and copper-clad aluminum, confirming the versatility and safety of the switch in various wiring applications.