If a Type NM cable has a stated ampacity, which conductor's rating must it not exceed?

The correct answer pertains to the ampacity ratings of conductors within NM (non-metallic) cable, which refers to the maximum amount of electric current a conductor or device can carry before sustaining immediate or progressive deterioration. For NM cable, the conductors are typically rated at 60°C when it comes to determining the proper ampacity.

In the context of electrical safety and performance, the ampacity for NM cables is primarily based on the temperature rating, which directly affects the amount of current the wire can safely carry. The 60°C rating is established as it incorporates the thermal characteristics of the cable and the environment in which it is used. Exceeding this temperature rating can lead to insulation failure and potential fire hazards.

While other temperature ratings such as 75°C and 90°C do exist (often for different types of conductors), they do not apply when determining the ampacity of NM cables which are specifically limited by their 60°C rating. Thus, when calculating or referencing the ampacity for Type NM cable, it is crucial to adhere to the 60°C conductor rating to ensure safety and compliance with electrical codes.