Cable selection against fire, halogen-free cable

How proper cable selection reduces fire accidents

Most electrical fires start when a cable overheats or a short circuit produces an arc that ignites the insulation or nearby material. Correct cable selection helps by:

1. Correct current rating: choosing a size whose current-carrying capacity (after derating for temperature, grouping and installation method) is more than the load current, so the cable does not overheat.
2. Matching protection: the fuse/MCB rating must be below the cable's capacity, so an overload trips the device before the cable overheats.
3. Short-circuit withstand: the conductor area must survive the fault current until protection clears it (A ≥ I√t/k). An undersized cable can melt and burn before the breaker trips.
4. Good-quality, standard cable: cables meeting IS/NS standards have the full copper/aluminium area and proper insulation. Cheap, under-sized "local" cables are a main cause of fires in Nepal.
5. Higher temperature insulation: XLPE (90 °C) instead of PVC (70 °C) where cables run hot.
6. Fire-retardant cables (FR / FRLS): the sheath does not spread flame along cable runs.
7. Voltage drop and loose-joint control: correct size and proper lugs avoid hot joints, which often start fires.
8. Proper installation: conduits, trays and fire barriers where cables pass through walls and floors.

Why halogen-free cable is important for fire fighting

Ordinary PVC contains chlorine, a halogen. When PVC burns it gives off:

• Thick black smoke, which blocks vision so people cannot find exits and fire fighters cannot see the fire.
• Hydrogen chloride gas, which is toxic, forms hydrochloric acid in the lungs and eyes, and corrodes electronic equipment.

Halogen-free (LSZH / LS0H, Low Smoke Zero Halogen) cables use halogen-free compounds. In a fire they:

• Produce little and light smoke, so escape routes stay visible.
• Release no toxic or corrosive halogen gases, so people can breathe longer and fire fighters can work safely.
• Cause less damage to equipment and the building.

So LSZH cables are used in hospitals, high-rise buildings, tunnels, shopping malls, data centres and other crowded or enclosed places. Fire-survival (FS) cables are used for fire alarms, emergency lighting and fire pumps, which must keep working during the fire.