BS 6387:2013 pdf download – Test method for resistance to fire of cables required to maintain circuit integrity under fire conditions
5 Test chamber Each test shall be carried out in a chamber with facilities for disposing of any noxious gases resulting from burning. Sufficient ventilation shall be available to sustain the burner flame for the duration of the test. The locations of any air inlets and exhaust chimney shall be such that the burner flame remains stable during each test protocol. For each test protocol, the same ventilation and shielding conditions as used for the verification of the source of heat shall be used. The temperature in the chamber shall be between 10 °C and 40 °C at the start of each test.
6 Protocol C for resistance to fire alone
6.1 Apparatus
6.1.1 Test rig, comprising a cable supporting system (6.1.2), a circuit continuity checking and voltage withstand arrangement and fuses (6.1.3 and 6.1.4) and a source of heat (6.1.5).
6.1.2 Cable supporting system, in which the cable sample under test is held horizontally by means of a suitable clamp at one end of the sheathed or protected portion and a support at the other end. The middle portion of the cable is supported by two metal rings placed approximately 300 mm apart and these as well as any other metal parts of the supporting apparatus are earthed. The cable supporting arrangement is shown in Figure 1. For unarmoured cables less than 10 mm in diameter, or for other cables where significant movement of the cable could occur during the test, the cable is supported by three additional metal supporting rings, each placed approximately 150 mm from the other two rings.
6.1.3 Circuit continuity checking and voltage withstand arrangement, comprising a three-phase star-connected transformer or three single-phase transformers (or one single-phase transformer if testing a single-core cable) of sufficient capacity to maintain the test voltage up to the maximum leakage current allowable, i.e. up to 2 A, and at the opposite end of the cable one or more lamps (with ballast resistor if necessary) connected to each core with a power rating such that each core carries a current of approximately 0.25 A at the rated voltage of the cable.
6.1.4 Fuses, IEC 60269-3:2010 Fuse system A–D, Type DII, 2A (Pink) or circuit breakers with equivalent characteristics. In case of dispute the use of fuses shall be the reference method.
6.1.5 Source of heat, comprising a tube-type gas burner with a burner face length of 610 mm ±10 mm, which produces a line of closely spaced flames using propane with a forced air supply. The temperature of the flames from the burner shall be set using a 1.5 mm Type K thermocouple conforming to BS EN 60584-1, using the following procedure. Insert the thermocouple into the flame position at the end of the burner closest to the gas inlet with the thermocouple parallel to the burner and situated 75 mm above it. With the thermocouple in position, light the burner and adjust the gas and air supplies until a flame temperature of 950 °C ±40 °C is steadily registered for at least 5 min. Record the values of gas and air flow and switch the burner off.
6.2 Cable sample The sample to be tested shall be a piece of the completed cable not less than 1 200 mm long, with approximately 100 mm of the sheath and outer coverings removed from each end. At the ends of the cable the conductors shall be prepared for electrical connections in accordance with the manufacturer’s recommendations.
6.3 Procedure Mount the cable sample in the clamp as described in 6.1.2 and adjust the metal supporting rings. Firmly clamp the cable at one end only. Connect the transformer or transformers to the conductors at one end of the cable, excluding any conductor that is specifically identified as intended for use as a neutral or protective conductor, as shown in the circuit diagram in Figure 2. For single, twin or three conductor cables, connect each conductor to be connected to a separate phase of the transformer output with a 2 A fuse or equivalent circuit breaker (6.1.4) in each phase. For cables with more than three conductors to be connected divide the conductors into three groups, ensuring that adjacent conductors are in different groups, as far as possible. Connect the conductors in each group in parallel and connect each group to a separate phase of the transformer output, with a 2 A fuse or equivalent circuit breaker in each phase.