If a raceway contains no more than 3 conductors, the ampacity must be ___.

• A. Increased
• B. Derated
• C. Maintained
• D. Reduced

Answer: (B)

When conductors share a raceway, heat buildup from all of them can raise the temperature of the insulation. Ampacity adjustments are used to account for that heat. Derating kicks in only when there are more than three current-carrying conductors in the same raceway or enclosure. With three or fewer current-carrying conductors, no derating is required, so you use the conductor’s listed ampacity at the given temperature rating. If you do have more than three, you apply a derating factor (lowering the allowable current) based on the exact number of conductors.