IEC 60331-31:2002 pdf download
IEC 60331-31:2002 pdf download.Tests for electric cables under fire conditions -ircuit integrity – Part 31: Procedures and requirements for firewith shock – Cables of rated voltageup to and including 0,6/1 kV.
3 Terms and definitions
For the purposes of this part of IEC 60331 the following definition applies.
circuit Integrity
ability to continue to operate In the designated manner whilst subjected to a specified flame source for a specified period of time
4 Test sample
4.1 Sample preparation
The sample to be tested shall be a piece of cable not less than 1 500 mm long with approximately 100 mm of sheath or outer coverings removed at each end.
At each end of the cable each conductor shall be suitably prepared for electrical connections. and the exposed conductors shall be spread apart to avoid contact with each other.
4.2 Sample mounting
The cable shall be bent to form an apploximate arc of a circle. The internal radius of the bend shall be the manufacturers declared minimum bending radius.
The cable shall be mounted centrally on the test ladder, as shown in figure 1, using metal clips which shall be earthed. Two U-bolts on the upper horizontal element of the ladder are recommended, but P-clips made of metal strip (10 ± 1) mm wide for cables up to 20 mm In diameter, and (20 ± 2) mm wide for cables Iron 20 mm up to 50 mm in diameter, and (30 ± 3) mm wide for larger cables shall be used on the central vertical elements. The P-clips shall be formed so as to have approximately the same diameter as the cable under test.
If the cable sample is too small to be mounted on the central vertical elements when in the position shown in figure 1, the vertical elements shall be equally moved towards the centre so that the cable may be mounted as shown in figure 2.
5 Continuity checking arrangements
During the test, a current for continuity checking is passed through all conductors of the cable this shall be provided by a three-phase star connected or single-phase transformer(s) of sufficient capacity to maintain the test voltage up to the maximum leakage current allowable.
NOTE I Due note Should be taken of the fuse ch.e,aetenstics when detern1nng the power 1*1mg of the tran5lormer
This current is achieved by connecting, at the other end of the sample, a suitable load and an indicating device (e.g. lamp) to each conductor, or group of conductors.
NOTE 2 A current of 0.25 A at the test voltage, through ,ich conductor or ‘oup of conductors, has bean found to be suitable.
6.4 At tile transformer end of the sample, earth the neutral conductor and any protective conductors. Any metal screens, drain wire or metallic layer shall be interconnected and earthed Connect the transformer(s) to the conductors, excluding any conductor which is specifically identified as intended for use as a neutral or a protective conductor, as shown in the circuit diagram in figure 3. Where a metallic sheath, armour or screen acts as a neutral or protective conductor, it shall be connected, as shown in the circuit diagram in figure 3, as for a neutral or protective conductor.
For single-, twin- or three-phase conductor cables, connect each phase conductor to a separate phase of the transformer(s) output with a 2 A fuse or circuit-breaker with equivalent characteristics in each phase
For multicore cables that have four or more conductors (excluding any neutral or protective conductors), the conductors shall be divided into three roughly equal groups, ensuring that adjacent conductors are, as far as possible, in different groups.
For multipair cables, the conductors shall be divided into two equal groups, ensuring that the a-core of each pair is connected to one phase and the b-core of each pair is connected to another phase (Li and L2 in figure 3), Quads shall be treated as two pairs.
For multi-triple cables, the conductors shall be divided into three equal groups, ensuring that the a-core of each triple is connected to one phase, the b-core of each triple to another phase and the c-core of each triple to the third phase of the transformer (Li. L2 and L3 In figure 3.).
