Methods of test

BS 7870-2:1999 pdf free.Lv and MV polymeric insulated cab les for use by distribution and generation utilities 一 Part 2: Methods of test (Implementation of HD 605).
2.1 Dimensional measurements
2.1.1 Measurement of insulation thickness
2.1.1.1 Procedure
The thickness of insulation shall be measured in accordance with BS EN 60811-1-1:1995, 8.1.
Conformity shall be checked on each core of cables having up to five cores, and on the number of cores stated
in the individual specification for cables with more than five cores.
2.1.1.2 Evaluation of results
The average of the values (expressed in millimetres), obtained as specified in the individual specification for the insulation from each core, shall be calculated to two decimal places and rounded off as given below. This shall be taken as the average value of the thickness of insulation.
If in the calculation the second decimal figure is five or more, the first decimal figure shall be raised to the next number thus, for example, 1.74 shall be rounded off to 1.7 and 1.75 to 1.8.
The lowest of all values obtained shall be taken as the minimum thickness of insulation at any place.
2.1.2 Measurement of non-metallic sheath thickness
2.1.2.1 Procedure
The thickness of sheath shall he measured in accordance with BS EN 60811-1-1:1995, 8.2
2.1.2.2 Evaluation of results
The average of the values (expressed in millimetres), obtained as specified in the individual specification for the sheath, shall be calculated to two decimal places and rounded off as given below. This shall be taken as the average value of the thickness of the sheath.
If in the calculation the second decimal figure is five or more, the first decimal figure shall be raised to the next number, thus, for example, 1.74 shall be rounded off to 1.7 and 1.75 to 1.8.
The lowest of all values obtained shall be taken as the minimum thickness of sheath at any place.
2.1.3 Measurement of cable dimensions
2.1.3.1 Measurement of overall dimensions
Unless otherwise specified the samples taken in accordance with 2.1.1 or 2.1.2 shall be used.
The measurement of the overall diameter of any circular cable and of the overall dimensions of flat cables with a major dimension not exceeding 15 mm shall be carried out in accordance with 13S EN 60811-1-1:1995, 8.3.
For the measurement of flat cables with a major dimension exceeding 15 mm, a micrometer, a profile projector or similar equipment shall be used.
The mean of the values obtained shall be taken as the mean overall dimensions.
2.1.4 Measurement of wires, strips and tapes
2.1.4.1 Conductor wires
Measurement of the diameter of conductor wires (class 5 conductors) shall be carried out as tollows.
a) Sampling
Take at random either 10 % of the total number of wires, rounded upwards, or 10 wires, whichever is the lowest, from one core of each length of cable selected for the test.
b) Method
Determine the diameter of each wire with a micrometer by taking a measurement in three positions. approximately 300 mm away from each other. The readings shall be made to two decimal places. Take the average of the three measurements to be the wire diameter.
2.1.4.2 Not applicable
2.1.4.3 Wires, strips and tapes for armour
Measurements shall be carried out as follows.
a) Round wires
Take at random 10 % of the total number of wires from a sample of completed cable. Determine the diameter of each wire by using a micrometer with flat noses and taking two measurements at right angles to each other. Take the average value as the wire diameter.
b) Flat wires or strips
Take at random 10 % of the total number of flat wires or strips from a sample of completed cable.
Determine the thickness and width of each flat wire by using a micrometer or vernier calliper with flat noses. Take the average values as the wire thickness and width respectively.
c) Metallic tapes thickness
Take and straighten a sample of each armour tape, remove the non metallic coating if any, and determine the tape thickness at six different places by using a micrometer or vernier calliper with flat noses. Take the smallest value to be compared with the specified thickness with a tolerance given in the particular specification.
2.1.5 Measurement of thickness of metallic sheath
Measurements shall be made by one of the following methods.
a) Strip method
The measurement shall be made on a test piece of sheath about 50 mm in length removed from the finished cable length. The test piece shall be taken a sufficient distance from the cable end to allow a proper measurement to be made.
The piece shall be slit longitudinally and carefully flattened. After cleaning the test piece, a sufficient number of measurements shall be taken along the circumference of the sheath and not less than 10 mm away from the edge of the flattened piece to ensure that the minimum thickness is measured. The
measurement shall be made with a micrometer with plane faces of 4 mm to 8 mm diameter and an accuracy of ±0.01 mm.
The average of the values (expressed in millimetres), obtained as specified in the individual specification for the sheath, shall be calculated to two decimal places and rounded off as given below. This shall be taken as the average value of the thickness of the sheath.If in the calculation the second decimal figure is five or more, the first decimal figure shall be raised to the next number, thus, for example, 1.74 shall be rounded off to 1.7 and 1.75 to 1.8.
The lowest of all values obtained shall be taken as the minimum thickness of sheath at any place.
b) Ring method
The measurements shall be made on a ring of the sheath carefully cut from the sample. The thickness shall be determined at a sufficient number of points around the circumference of the ring to ensure that the minimum thickness is measured.
The measurements shall be made with a micrometer having either one flat nose and one ball nose, or one flat nose and a flat rectangular nose 0.8 mm wide and 2.4 mm long. The ball nose or the flat rectangular nose shall be applied to the inside of the ring. The accuracy of the micrometer shall be ±0.01 mm.
2.1.6 Not applicable
2.1.7 Not applicable
2.1.8 Measurement of the gap between non-metallic tapes of taped bedding
Measure the gap between the adjacent edges of each bedding tape at right angles to the tape. and also the tape width, on a sample of cable 300 mm long, taken not less than 150 mm from the end of a factory length.
Take the measurements by any suitable means in which the error of determination does not exceed 0.5 mm. Measure the gaps at four positions approximately 50 mm apart along the length of the sample.BS 7870-2 pdf free download.Methods of test