Ambient temperature of the area where the wire will be installed is a factor in determining wire size because it affects what?

• A. System voltage
• B. Current-carrying capability
• C. Ambient temperature has no effect
• D. Color of insulation

Answer: (B)

Current-carrying capability, or ampacity, is the key factor here. The amount of current a conductor can safely carry depends on how well it can shed the heat produced by the current. Ambient temperature affects that heat dissipation: in a hotter environment, heat does not escape as effectively, so the conductor heats up more for the same current. To keep the conductor within its insulation’s temperature limits, engineers apply derating factors to the ampacity, which can mean using a larger wire or reducing the current. System voltage and insulation color don’t determine how much current the wire can safely carry, and ambient temperature does have an effect.