NEC Commercial Electrical Practice Test

What is the temperature rating required for the insulation of conductors within type NM cable?

1. 60°C

2. 75°C

3. 90°C

4. 100°C

The correct answer is: 90°C

The correct temperature rating for the insulation of conductors within type NM (non-metallic) cable is 90°C. This rating is significant because it indicates the maximum temperature that the insulation can safely withstand without degrading or leading to potential hazards, such as electrical shorts or fires. Type NM cable is commonly used in residential applications for circuits such as lighting, outlets, and appliances. The 90°C rating is important for ensuring that the conductors can handle higher temperatures that might occur during operation without compromising the integrity of the insulation. This allows for better performance under load and increased safety, especially in environments that may experience heat buildup. The various temperature ratings that are provided in the choices reflect different types of wire insulation materials. Conductors rated at 60°C and 75°C could be used in specific applications but do not meet the requirements for NM cable. Therefore, selecting the 90°C rating acknowledges the standard practices and safety measures essential in electrical installations.