UL 1424-2015 pdf download
UL 1424-2015 pdf download.Cables for Power-Limited Fire-Alarm Circuits.
28.3 For every continuous period of 3 weeks dunng the latter halt of the 12•week immersion, a smooth curve drawn covering the entire immersion period and showing the average of the measured readings of insulation resistance shall not decrease at a rate exceeding 4 percent per week. A coil that shows a greater percent decrease in insulation resistance during the extended immersion than specified in 28.2 shall be tested 104’ additional 1-week immers4on periods and the coil is to be evaluated based on the last 12 weeks of immersion.
28.4 To determine whether or not the insulation complies with the requirements In 28.2 and 28.3 the center 50-toot (20-meter) sections of three 55-foot (22-meter) coils of the insulated conductor are to be immersed in tap water at the specified temperature for the duration of the test. The ends of each specimen are to be brought well away from the tank. and the water ie to be maintained at the specified temperature.
28.5 The insulation-resistance test equipment and procedures shall be applicable. Otherwise they are not specified. A megohm bridge used for this purpose shall be of applicable range and calibration and shall present readings that are accurate to 10 percent or less of the value indicated by the meter. A d-c potential of 100 — 500 V shall be applied to the insulation for 60 s prior to each reading. Each galvanometer indication shall be given 60 $ to stabilize before the reading is recorded. The duration of each reading shall be 60 s in the case of range switching or lot metenng equipment requiring time to achieve a null. Delay is not required for instant-reading equipment that has been demonstrated to produce correct readings without a 60-s delay.
29 Test Procedure for Determining the Multiplying-Factor Column for Adjusting Insulation Resistance
29.1 Two specimens, conveniently of a 16 — 20 AWG solid conductor with a wall of insulation whose average thickness is 10 — 15 mils ci’ 0.25 — 0.38 mm are to be selected as representative of the insulation under consideration. The specimens are to be 01 a length (at least 200 ft or 60 m) that yields insulation-resistance values that are stable within the calibrated range of the measuring instrument at the lowest water-bath temperature.
29.2 The two specimens are to be immersed in a water bath equipped with heating, cooling, and
circulating facilities. The ends of the specimens are to extend at least 2 ft or 600 mm above the surface of the water to reduce electrical leakage. The specimens are to be left in the water at room temperature for 16 h before adjusting the bath temperature to 50.0°F (10.0°C) or before transferring the specimens to a 50.0°F (10.0°C) bath.
29.3 The d-c resistance of the metal conductor is to be measured at applicable intervals ot time until the temperature remains unchanged for at least 5 mm. The insulation is then to be considered as being at the temperature of the bath indicated on the bath thermometer.
29.4 Each of the two specimens is to be exposed (29.3 applies) to successive water temperatures of 50.0,61.0.72.0,82.0, and 95.0°F (10.0, 16.1,22.2,27.8, and 35.0°C) and returning, 82.0,72.0,61.0. and 50.0°F (27.8,22.2, 16.1, and 10.0°C). Insulation-resistance readings are lobe taken at each temperature after equilibrium is established.
29.5 The two sets of readings (four readings In all) taken at the same temperature are to be averaged for the two specimens. These four average values and the average of the single readings at 95.0°F (35.0°C) are to be plotted on semilog paper. A continuous curve (usually a straight line) is to be drawn through the five points. The value of insulation resistance at 60.0°F (15.6°C) is then to be read from the graph.
