Basic test method for wire and cable <br>Basic structure (1) Conductor
1. Conductor resistance: In addition to tin core wires such as TPT, TS and TST, UL does not require measurement of conductor resistance of wire and cable products.
2, wire diameter: usually the wire diameter of wire and cable are even AWG, such as 18AWG, 16AWG, etc., odd-numbered AWG wire is a special exception.
3. There are two ways to determine the cross-sectional area of ​​a conductor:
A. Measure the sum of the cross-sectional areas of each stranded core. The average of the diameters of the seven twisted wires should be taken as the average core diameter. D
Calculated in Mils: conductor cross-sectional area CMA = nd2 (CMA: Circular Mil Area)
Calculated in millimeters: conductor = 0.7854 * nd2
Where n is the number of cores in the conductor structure. Measurement of core diameter: According to Section 2 of UL1581, each core wire diameter shall be measured with an accuracy of 0.01 mm (0.001 inch), and both end faces are flat micrometers.
B. Weighing method, see section 210 of UL1581.
The measured value was found to be less than the required value during the measurement (UL1581, Table 20.1) and can be confirmed by the other of the two methods. (Note: The DC resistance measurement method cannot be used as the final judgment criterion for measuring the CMA.)
Conductor insulation thickness
1, measuring tools: micrometer commonly used micrometer, measuring end faces are flat, zui small reading: 0.01mm
The load surface is 1.98*9.5mm, and the load micrometer with a load of 10g (conductor insulation thickness)
Measurement of average insulation thickness: starting from 10 inches from the end line, one measurement point per 10 inches, measuring the outer diameter of the wire at 5 points, the diameter of the conductor.
Insulation thickness = (wire outer diameter - conductor diameter) / 2
The average insulation thickness is obtained by averaging the insulation thicknesses at 5 points.
Zui small insulation thickness measurement:
Measuring tool: pin-gauge micrometer, note that this method is suitable for wire structures of 18AWG or larger. Intercept the insulator of the core conductor and place it on the pin of the micrometer. When measuring, first gently raise the load and slowly rotate the insulator. The small value of zui is regarded as the small thickness of the wire insulator. For wires less than 18 AWG, a reading microscope method can be used.
2. Measurement tool. When sampling the microscope, carefully draw all the conductor cores, slice them vertically along the wire insulator, and measure the thickness of the thin zui under the microscope as the small thickness of the conductor insulation layer.
The measurement result of the reading microscope (accuracy of 0.001 mm) is usually used as the reference standard for Zui. In the actual measurement, it was found that the thickness of the zui measured by one coil of wire was less than the specified value more than 2Mils, and it was judged that the coiled wire was unqualified. If the measured value is less than the specified value and does not exceed 2Mils, two sample measurements shall be taken at a distance of 1 foot from the coil wire. If one of the results is less than the small value of zui, the coil wire is judged as unqualified, if both measurements are Achieved the standard and was judged as qualified.
The outer diameter is measured by the outer diameter of the outer diameter at 5 points of the outer diameter of the outer diameter and the diameter of the cable, and the outer thickness = (outer outer diameter - cable diameter) / 2
The average outer thickness is the average of 5 point measurements.
Outside is small thickness of zui: small insulation thickness of the same wire zui. The outer surface of the outer surface shall be carefully polished and leveled, and then a load of 85 g and a load micrometer measuring a cross-sectional diameter of 6.4 mm shall be used.
Reading Microscope Measurement: The method is the same as the conductor insulation thickness measurement method.
A comparison table of the average thickness of common wires and the small thickness of zui. See UL62, Table: 16.2, 16.4, 16.6, 16.8.
The average value of the 10 strands of the stranded core strands is taken as the average strand pitch of the core. The insulation sheath of about ten strands is removed during the measurement, and any one of the cores is taken for measurement. Be careful not to damage the core wire when peeling, causing the core wire to break.
The wire lay length is also averaged from the 10 lay lengths of the wire. As the average wire lay length, it is necessary to pay attention to the internal stress caused by the wire stranding when the wire is twisted. When the outer cover is removed, the original stranded structure may be loose. . For this reason, when sampling, first reserve a sheathed wire to remove the outer cover, and then pull off part of the outer cover with the sharp blade in the direction of the cable. The Zui is able to see the wire to be tested, and the wire is combined with the outer casing. Very close. Straighten the sample and straighten it, and measure the distance between the ten twisted points of a certain wire as the lay length. Because of the stress relationship during the cable formation, the original stranding distance will increase.
See UL62 for various core wire zui large lay lengths. For the wire diameter of various wire diameters, see UL62
(2) Burning test wire burning grade and test method comparison table continued (3) The voltage corresponding to UL62Table51.1 should be applied between the wires in the withstand voltage test cable. When pressing, the voltage should be slowly changed within 10S to 60S. Add zero to the nominal value for 1 minute. The criterion is that the Hi-pot circuit alarms during the rise, fall, and hold periods. On the other hand, the insulation resistance test can produce similar effects in some programs, so first performing the withstand voltage test is a positive and easy way to test the leakage.
(4) Spark test For single-core power lines, such as CXTW lines, the withstand voltage test is the spark test, while for the multi-core power line, the spark test can be used instead of the withstand voltage test in the daily production test.
Spark test points:
Spark testing machine (1) chrome-plated copper beads length, position: See Table 900.1, from the horizontal and vertical direction of the bead training interval, arrangement, etc., in daily production must be regularly checked whether the beads are dropped, such as found Some are incomplete and should be replaced in time.
(2) The relationship between the length L of the V-shaped test slot of the spark machine, the test frequency, and the large outlet speed of the production wire, see Table 900.2. It can be seen that the working frequency is increased, the outlet rate can be greatly improved, and the production efficiency can be greatly improved.
(3) Grounding of the line: Keep the conductor and the grounding and retracting wheel and the sparking machine well grounded.
The wire end is bare copper wire: the wire end is grounded, the wire end is not grounded, and the wire continuity is not required to be tested.
The pay-off end is an insulated wire: the wire is connected to the take-up wire and the pay-off wheel, and the wire-receiving and pay-off ends must be grounded. For 10AWG or thinner wires, the continuity performance is not tested.
Test voltage: see Table900.2
(5) Insulation resistance test
1. The common wire and cable insulation high resistance meter DC voltage is adjusted to 100-500V, and the length of the 50FT-5000FT wire is immersed in the water tank for 2 hours. One electrode of the high resistance meter is connected to the copper plate electrode of the water tank, and the other electrode is connected to On the wire lead to be tested. The measurement time is 60 seconds, and the insulation resistance of the 1000-foot wire is greater than 2.5M when the qualified standard is 15.6 °C.
The measured value of the water temperature from 10 °C to 29.4 °C is converted to a value of 15.6 °C and a length of 1000 feet:
R*L*M*TCF
1000
R: high resistance meter reading L: measured wire length
M: high resistance meter ratio TCF: temperature correction coefficient
TCF comparison table can be found in UL1581 Table52.1
2, commonly used outdoor "w" wire and cable, such as SPT-2W, SJTW, CXTW and so on.
The test method for short-time insulation resistance is the same as that of ordinary wire and cable, but the qualification criteria are completely different, and the resistance of the "W" wire is much higher. For example, CXTW22AWG, the pass standard is 15.6 ° C 225 M / 1000 ft.
(1) Judging criteria
SPT-2W, SPT-1W, XTW and CXW, see UL62Table35.1
SJTW and other sheathed wires, see UL62Table32.1
The insulation resistance listed in the table is the short-time immersion resistance at 15.6 °C, and the insulation resistance is tested by heating at 50 °C for a long time.
(2) Determination of TCF First, determine the impedance factor C, and then find the corresponding M factor from UL62Table33.1, and apply the previous formula to find the impedance.
Note: For sheathed cables, such as SVT, SJTW, the insulation resistance listed in the table is the insulation resistance between the wires in the sheath. Therefore, when measuring, the outer sheath should be removed and then immersed in water.
Determination of impedance factor C: See UL62, section 34.
Principle: During the heating and cooling of two samples, the resistance values ​​of five fixed temperature points were measured, plotted on semi-logarithmic coordinates, the resistance at 15.6 °C was calculated, and the resistance at 16.1 °C was read. The C value can be obtained by dividing the two.
(6) Tensile test before aging and after aging
1. How to determine the stretching speed of the test machine?
Tensile rate: When the stretching rate is not specified in the table in section 50 of UL1581, the rate is usually 500+25mm/min.
2. How to determine the stretch index of the material?
UL62 has now attributed the physical properties of conventional bendable cords to Table 5.2 (insulator) and Table 7.2 (outer quilt).
In the past, all physical properties of wire and plastic materials were listed in the UL1581 Table50 series. For example, SPT-2, 105 ° C wire, its physical properties are: SPT-2 is Integral PVC cable, so apply UL62Table15.1 or UL1581 Table50182. 105 °C corresponding CLASS is 2.11, stretch %
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