The protective effect of a fire-retardant coating on the insulation failure of PVC cable

• We studied the protective effect of fire retardant coating for PVC cable.
• The failure time is increased along with the thickness of the coating.
• Inserting the coated conduit is more significant, and the failure time is much longer.
• The studied methods are not appropriate to protect long time working cables in fire.

The failure time of polyvinyl chloride (PVC) insulated power cables was studied using an infrared radiation heating furnace and insulation resistance measurements. The temperature–time curve inside the furnace was similar to that of the ISO 834 standard. Two popular fire protection methods were employed for the cables; one method applied fire-retardant coatings directly on the cable surface, and the other inserted the cables into metal conduits coated with structural steel fire-retardant coating. The results showed that for both protection methods, the failure time of the cable increased with the thickness of the coating. However, if the cable coatings were thicker than 1.5 mm, the coating will crack in the case of cable movement. When the steel structural coating was thinner than 1 mm or thicker than 3 mm, the protective effect was not remarkable for the relatively small expansion multiple. For the longest failure time of the cables, less than 10 min in these tests, neither of the two methods was effective in protecting the electrical cables that supply power (on transmit a signal) to equipment required to operate over a relatively long duration in fire conditions.