UL 1030-2017 pdf download – Sheathed Heating Elements.
6 Insulation 6.1 An insulating washer, a bushing, or the like, that is an integral part of a heating element shall be of a material resistant to moisture, such as porcelain, and shall be acceptable for use at the maximum temperature to which it will be subjected under conditions of actual use. Such parts shall have adequate mechanical strength and rigidity to withstand the stress of actual service. 6.2 Insulating material employed in an integral part of a heating element, such as a terminal block, or the like, shall be strong, not easily ignited, and resistant to moisture. A material other than porcelain, phenolic, or one that is known to be acceptable for the support of current-carrying parts shall be investigated under conditions of actual service to determine if it has the necessary electrical and mechanical properties and will withstand the most severe conditions likely to be met in service. 6.3 The thickness of magnesium oxide (MgO) or other similar insulating material between the resistance element and the inside of the sheath, and the material of an end seal between the terminal pin and the inside of the sheath shall not be: a) Less than 0.016 inch (0.41 mm) for elements rated 300 volts or less, and b) Less than 0.031 inch (0.79 mm) for elements rated more than 300 volts. 7 Spacings 7.1 A spacing, through air and over surface, of not less than 1/16 inch (1.6 mm) between live parts of opposite polarity and between live parts and dead metal parts shall be maintained at or near the end of the sheath of a heating element rated 300 volts or less. For an element rated more than 300 volts, the spacings at the end of the sheath shall not be less than 1/4 inch (6.4 mm). Exception No. 1: When exact centering of a terminal pin is required to maintain the 1/16 inch spacing, a spacing of3/64 inch (1.2 mm) in one location meets the intent ofthe requirement.
10.1.2 When a 3-phase source of supply is not available, and when it is agreeable to those concerned, the single-phase test described in 10.3.1 may be conducted instead of the test described in 10.2.1. The dielectric and power supply voltages are to be monitored to ensure that they are 1 80 degrees out-of-phase. Otherwise, the summation of the in-phase cycles will result in a net test potential in excess of what is required in Table 10.1. 10.1.3 To determine whether a heating element complies with the requirement in 10.1.1, the heating element is to be tested by means of a 500-volt-ampere or larger capacity transformer, the output voltage of which is essentially sinusoidal and can be varied. The applied potential is to be increased from zero until the required test level is reached, and is to be held at that level for one minute. The increase in the applied potential is to be at a substantially uniform rate as rapid as is consistent with correct indication of its value by a voltmeter.