What is the maximum allowable ampacity for Type NM cable in relation to a rated conductor?

The maximum allowable ampacity for Type NM cable is determined by the temperature rating of the conductors within the cable. In the context of Type NM cable, which commonly contains conductors rated for use at 60°C (140°F), this is the temperature at which its ampacity is defined.

When considering wiring, the temperature rating is crucial because it directly impacts the ability of the wire to carry current safely without exceeding the heat dissipation capabilities of the conductor’s insulation. Therefore, the ampacity values specified for conductors take the temperature rating into account.

Using Type NM cable rated at 60°C, the ampacity must be looked up in the appropriate tables (usually found in the National Electrical Code or similar standards), confirming that the values listed are indeed relevant for conductors with that rating. This is critical for ensuring that installations meet safety and performance guidelines.

While there are higher temperature ratings for other types of conductors (such as 75°C, which is typical for many insulated copper and aluminum conductors), Type NM cable specifically adheres to the 60°C standards, which ensures the necessary safety margin when used in residential applications. Hence, the correct answer reflects the standard practices for this type of wiring.