IEC 60331 Tests for electric cables under fire conditions - Circuit integrity

Great, considerable damage at person and real value may occure through the combustion of thermoplastic cables. Professional installations of standard cables are operationally safe and doesn`t cause a fire. A fire may spread more or less along cables or the cables may lighted more or less depending on kind of cable type, used insulation and sheathing materials, and installation conditions, caused by appearing of an additional source of fire. Depending on the extent and temperature of the fire the electrical function of a cable (short circuit) and of the connected electrical equipment can not be guaranteed. Important functions like emergency lighting, lift, air conditioning etc. in public buildings have to be kept during a fire. During a fire in industrial plants the manufacturing processes may be finished ceckable to aviod large industrial accidents.
For testing of insulated wires and cables concerning the fire resistance, the following tests are available:

IEC 60331-11: Apparatus – Fire alone at a flame temperature of at least 750 °C
IEC 60331-21: Procedures and requirements – Cables of rated voltage up to and including 0.6/1 kV
IEC 60331-22: Procedures and requirements – Cables of rated voltage above 0.6/1 kV
IEC 60331-23: Procedures and requirements – Electric data cables
IEC 60331-22: Procedures and requirements – Optical fibre cables

General construction notes of cables £ 0,6/1 kV with fire resisting characteristics To guarantee the fire resistance and also the function of the cables, the conductors should be insulated with a material, which at the same time withstands the heat of a fire and keeps the insulation effect. About
this mineral materials (mineral insulated cables), mica tapes, or materials which form a fire protection sheath during the combustion are outstandingly.

If MICA-tapes are used to fulfill the fire resistance, an additional electrical insulation has to be extruded over the MICA-tape wrapped conductors. This insulation is also used as mechanical protection to prevent damages at the MICA-tapes. In the reason of conductable acids zero halogen insulation materials have to be used. Because the acids will come through the MICA-tapes and conduct the current between the conductors (short circuit). Sheaths (unarmoured cables) or beddings (armoured cables) directly applied over the cable core have to be zero halogen, too.

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