What happens to thermoplastic conductor insulation when overheating occurs?

When thermoplastic conductor insulation is subjected to overheating, the most notable effect is sagging. This occurs due to the nature of thermoplastic materials, which are designed to become pliable when heated. As the temperature rises, these materials lose their structural integrity and can begin to droop or sag under their own weight.

This sagging can lead to diminished protective qualities and can potentially expose the conductor to environmental hazards, increasing the risk of electrical shorts and fires. Thermoplastic materials do not harden or crack in the same way that thermosetting plastics do—thermosetting plastics typically become rigid and cannot be remolded upon reheating.

While melting could occur at extremely high temperatures, it is the sagging effect that is more characteristic of the initial response to overheating in thermoplastic insulation, as it signifies a loss of mechanical properties without the material fully transitioning into a liquid state. Therefore, the sagging is a critical indicator of the insulation's compromised condition in the event of overheating.