Journeyman Electrician Practice Exam

When using Type UF cable as a substitution for Type NM cable, what should the conductor insulation rating be?

1. 60°C

2. 75°C

3. 90°C

4. 105°C

The correct answer is: 90°C

When using Type UF (Underground Feeder) cable as a substitution for Type NM (Non-Metallic Sheathed) cable, it is crucial to recognize that the conductor insulation rating must be appropriate for the environment where it is installed. Type UF cable uniquely features conductors that are thermoplastic insulated, typically rated for a maximum temperature of 90°C. This higher temperature rating allows Type UF cable to be utilized in various applications, including underground installations, where it may encounter more challenging conditions than what Type NM cable typically considers. Type NM cable, on the other hand, is generally rated for a maximum of 90°C as well under normal uses but has limited use in damp or wet locations, where UF cable is more suitable. Having a conductor insulation rating of 90°C for Type UF ensures that the wire can safely handle higher temperatures, providing a margin of safety and reliability in its rated applications. This is especially important in environments where heat buildup could occur, whether from environmental factors or the amount of current flowing through the conductors. Thus, the necessity for adherence to this temperature rating stands crucial for safety, performance, and compliance with electrical codes.