Fire Testing

4. Circuit (insulation) Integrity in accordance with BS 6387:1994
BS 6387:1994 specifies the requrements for cables required to maintain circuit integrity under fire conditions. This is the first standard to include also mechanical stress and water stress in the fire resistance test of electric cables. BS 6387 standard is still used in many countries. Being different from EN 50200, Its limits is to require three different tests on three different cable samples.
The fire resistant cables are categorized by a letter symbol (e.g. A) or series of symbols (e.g. CWZ) according to the requirements for fire resistance characteristics which they meet, the test temperature selected and the duration of the test for resistance to fire alone in according to BS 6387 as below:
The test provides the basis for the following categories:

Test	category
( 1 ) Resistance to fire alone
650°C for 3 hours	A
750°C for 3 hours	B
950°C for 3 hours	C
950°C for 20 minutes (short duration)	S
( 2 ) Resistance to fire with water Exposed to fire @ 650°C for 15 mins then exposed to fire @ 650°C with water for another 15 mins.	W
( 3 ) Resistance to fire with mechanical shock
Exposed to fire @ 650°C for 15 mins then exposed to fire @ 650°C with	X
mechanical shock for 15 mins.
Exposed to fire @ 750°C for 15 mins then exposed to fire @ 750°C with	Y
mechanical shock for 15 mins.
Exposed to fire @ 950°C for 15 mins then exposed to fire @ 950°C with	Z
mechanical shock for 15 mins

The most common test comprises the three categories C, W and Z.
–Category C is a fire resistance test in which the cable is exposed to a fire at a temperature of
950°C with a duration of 3 hours. under realistic conditions.
– Category W is a fire and water resistance test in which the cable is exposed to a fire at a temperature of 650°C and then for another 15 minutes to fire with water that is poured over the area around the cable. This simulates effect of water from a sprinkler that is activated during the fire. -Category Z is a fire and mechanical stroke test in which the cable is installed in a defined manner on a vertical wall with three cable clips and subject to heat from a gas burner; mechanical shock is simulated by striking the cable with a hammer. The cable is exposed to a fire at a temperature of 950°C and then for another 15 minutes to fire with mechanical shock at a frequency of 2 strikes per minute.
During testing in all three categories, the cable is connected to a 400V three-phase power supply
protected with a 3 A fuse on each phase. The test is regarded as successful if none of the fuses blow
during the test period.