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UL 8750-2020 pdf free download
UL 8750-2020 pdf free download.Light Emitting Diode ( LED ) Equipment for Use in Lighting Products.
8.3.9 A unit intended to be used inside of a luminaire shall be supported in a test oven with its mounting surface down and 76 mm (3 in) above the base of the enclosure in a central position on two 76 mm (3 in) wooden or ceramic cleats. To determine the temperature produced on the device surface, thermocouples shall be attached to the case in the areas of major heat sources. Temperatures on the device case shall be determined by means of thermocouples, and in the coils by the thermocouple or rise-of-resistance method. The unit shall be conditioned in the test oven until all parts reach the temperature of the heated air therein pnor to the test.
8.3.10 For a unit with potting it would be necessary to apply thermocouples to interior components prior to potting.
8.3.11 A thermocouple junction and the adjacent thermocouple lead wire are to be securely held in thermal contact with the surface of the material of which the temperature is being measured. In most cases, adequate thermal contact will result from securely taping or cementing the thermocouple in place:
but, if a metal surface is involved, brazing or soldenrig the thermocouple to the metal may be necessary.
8.3.12 It may oe necessary to test a modilied sample. witfl adaitiona’ ieaa wires that are extended, so that the temperature of each coil of a device may be measured by the resistance method.
8.3.13 The following explanation pertains to coil insulation temperatures. The insulation system temperature (class) is also the internal hot spot temperature limit. The average coil temperature, obtained by the change of resistance method, is the average of the entire coil from internal hot spots to the cooler, outer surface; hence, the average limit is lower than the internal hot spot, or system limit. The thermocouple measurement method gives the temperature of the cooler, outer surface; hence, the outer surface limit is lower than the average limit. In end-product applications, the thermocouple measurement method is primarily for convenience. At the point on the surface of a device where the temperature is affected by another source of heat, the temperature may exceed the value given in Table 8.1 provided the average temperature is not exceeded
8.3.14 The temperature on a coil may be measured by the thermocouple method or determined by the change-of-resistance method (comparing the resistance of the winding at the temperature to be measured with its resistance at a known temperature) using the formula specified below.UL 8750-2020 pdf free download.
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