When bare conductors are installed with insulated conductors, their ampacities shall be limited to which option?

• A. the most restrictive insulation rating among the insulated conductors
• B. the highest temperature rating of any insulated conductor
• C. the lowest temperature rating for any insulated conductor
• D. the insulation thickness

Answer: (C)

When bare conductors share a raceway or cable with insulated conductors, the heat in the assembly comes from all the conductors and there’s no insulating material on the bare ones to slow heat buildup. To protect the insulation on the insulated conductors, the current carried by the bare conductors must be limited to the level allowed by the lowest temperature rating among the insulated conductors. That ensures the temperature in the bundle doesn’t exceed what any insulation can safely handle.

The other ideas aren’t the controlling factor: using the highest temperature rating would let more current at risk of overheating; insulation thickness isn’t what determines the allowed ampacity in this scenario; and while the most restrictive insulation rating is related, the standard practice is specifically tied to the lowest temperature rating of the insulated conductors.