What is the minimum THHN conductor size that must be used from a 15-amp circuit to the fire alarm control panel?

What is the minimum THHN conductor size that must be used from a 15-amp circuit to the fire alarm control panel?

• A. #14
• B. #12
• C. #16
• D. #18

Answer: (A)

The main idea here is that conductor size must match the circuit’s current-carrying capability (ampacity). A 15-amp circuit needs a conductor that can safely carry at least 15 A. For copper conductors with THHN insulation, the smallest size that provides at least that ampacity is 14 AWG. Using a smaller size would risk overheating, while a larger size is allowed but not the minimum required. So from a 15-amp circuit to the fire alarm control panel, the minimum THHN conductor size you must use is 14 AWG.

The main idea here is that conductor size must match the circuit’s current-carrying capability (ampacity). A 15-amp circuit needs a conductor that can safely carry at least 15 A. For copper conductors with THHN insulation, the smallest size that provides at least that ampacity is 14 AWG. Using a smaller size would risk overheating, while a larger size is allowed but not the minimum required. So from a 15-amp circuit to the fire alarm control panel, the minimum THHN conductor size you must use is 14 AWG.