Maximum flame spread distance for combustible electrical wires and cables and optical fiber cables exposed within a plenum is how many feet?

Maximum flame spread distance for combustible electrical wires and cables and optical fiber cables exposed within a plenum is how many feet?

• A. 5
• B. 10
• C. 15
• D. 20

Answer: (A)

In a plenum, flame propagation along exposed combustible cables is tightly limited to reduce how far a fire can spread through the air-handling space. The tested rule sets a maximum of five feet for the flame spread along exposed combustible electrical wires, cables, and optical fiber cables. This short distance helps prevent a small ignition from turning into a larger, more dangerous fire and keeps smoke production manageable in a duct or air distribution path. If more than five feet of exposure could occur, the typical approach is to route or protect the cable so the flame path is interrupted or use plenum-rated cable designed for such spaces. The other, longer distances would allow fire and smoke to travel much farther before containment, which is not acceptable in a plenum setting.

In a plenum, flame propagation along exposed combustible cables is tightly limited to reduce how far a fire can spread through the air-handling space. The tested rule sets a maximum of five feet for the flame spread along exposed combustible electrical wires, cables, and optical fiber cables. This short distance helps prevent a small ignition from turning into a larger, more dangerous fire and keeps smoke production manageable in a duct or air distribution path. If more than five feet of exposure could occur, the typical approach is to route or protect the cable so the flame path is interrupted or use plenum-rated cable designed for such spaces. The other, longer distances would allow fire and smoke to travel much farther before containment, which is not acceptable in a plenum setting.