Which type of conductor is known for being the smallest in outside diameter and lowest in cost for 600V applications?

• A. Concentric
• B. THHN
• C. Type SE
• D. Type UF

Answer: (B)

The best choice for being the smallest in outside diameter and the lowest in cost for 600V applications is THHN. This type of conductor is specifically designed for use in general wiring and is made of copper or aluminum, which contributes to its compact size and cost-effectiveness. THHN stands for Thermoplastic High Heat-resistant Nylon-coated, indicating that it can withstand higher temperatures and is suitable for various applications, making it versatile and economical.

Concentric conductors, while they are used for power distribution and have a different structural approach, do not typically fall within the parameters of being the smallest or the most cost-effective for general wiring applications at 600V. Type SE, which refers to Service Entrance conductors, is larger and designed specifically for bringing power to a building, and Type UF, which is used for underground feeder wiring, also tends to be bulkier than THHN. These differing uses and construction factors highlight why THHN stands out in this context as the most appropriate choice.