AC and DC conductors rated 1,000 V or less may occupy the same space provided that all conductors have what property?

• A. The same color insulation
• B. Insulation rating equal to the maximum voltage
• C. Same gauge
• D. Listed for use in the same space

Answer: (B)

All conductors placed in the same space must be able to withstand the highest voltage present in the installation. That means every conductor’s insulation must be rated for the maximum system voltage (in this case, 1,000 V or higher). If any conductor has insulation rated lower than that, it could break down and allow arcing or insulation failure against neighboring conductors, which is the fundamental safety concern when mixing AC and DC in the same space.

Color, gauge, or whether the item is listed for the space doesn’t set the required voltage stress the insulation must handle. The key requirement is that the insulation rating matches or exceeds the maximum voltage in the installation.