How does ambient temperature affect conductor ampacity?

How does ambient temperature affect conductor ampacity?

• A. Higher ambient temperatures reduce ampacity so de-rating may be required.
• B. Higher ambient temperatures increase ampacity.
• C. Temperature has no effect on ampacity.
• D. Ampacity increases with higher ambient temp.

Answer: (A)

Ambient temperature sets the surrounding heat pressure the conductor must contend with. Ampacity is defined based on a standard reference ambient temperature, because insulation limits and allowable temperature rise are what determine how much current the conductor can safely carry. When the surrounding temperature rises, the conductor will reach a higher temperature for the same current. To keep the insulation from overheating, the current must be reduced—this is de-rating. So, as ambient temperature increases, the allowable current decreases, which is why higher ambient temps reduce ampacity and require adjustment using temperature correction factors. The idea that temperature has no effect or that ampacity increases with warmer temperatures isn’t consistent with the need to prevent insulation damage and overheating.

Ambient temperature sets the surrounding heat pressure the conductor must contend with. Ampacity is defined based on a standard reference ambient temperature, because insulation limits and allowable temperature rise are what determine how much current the conductor can safely carry. When the surrounding temperature rises, the conductor will reach a higher temperature for the same current. To keep the insulation from overheating, the current must be reduced—this is de-rating. So, as ambient temperature increases, the allowable current decreases, which is why higher ambient temps reduce ampacity and require adjustment using temperature correction factors. The idea that temperature has no effect or that ampacity increases with warmer temperatures isn’t consistent with the need to prevent insulation damage and overheating.