UL 1996:2009 pdf download – Electric Duct Heaters
UL 1996:2009 pdf download – Electric Duct Heaters.
27.5 Outlet air
27.5.1 On the outlet side of the heater or heaters, the main supply duct is to terminate at and discharge into an attached outlet duct of the same cross-sectional area. The outlet duct is to extend away from and at right angles to tne main supply duct for a distance of 914 mm (36 inches) or more, measured to the inside corner of the connected ducts. A grid consisting of nine thermocouples of identical length wired in parallel is to be installed in the outlet duct to measure the temperature of the outlet air. The thermocouples are to be located In a plane perpendicular to the axis of the duct, and:
a) For a rectangular duct — each located at the center of an equal sized rectangular area with the areas arranged in three rows to cover the entire oss section, or
b) For a round duct — one located at the center and the others equally spaced along the
circumference of a concentric circle having a radius of two-thirds of the duct radius. The grid Is to be located no more than 152 mm (6 inches) downstream from the location nearest to the
heater at which no thermocouple is affected directly by radiation from the heating element, and not less than 152 mm (6 inches) from the outlet end of the outlet duct.
27.6 Test enclosure
276.1 Except as noted in 27.6.4, a wooden test enclosure, see Figure 27.1 • is to be employed to enclose the main supply, and outlet ducts, and is to extend at least 1.2 m (4 feet) on either side of the heater or heaters wi the main supply duct. The enclosure Is to be made of 19 mm (3/4 inch) plywood or boards having a nominal thickness of 25.4 mm (1 inch). The inside surfaces are to be painted flat black, and all joints are to be sealed.
28.10 In conducting a test to determine when a heater complies with the temperature requirements, it is to be mounted or supporled as In service and tested under conditions of intended operation, except as otherwise noted, Temperatures are to be taken on nearby surfaces, on the supporting surface, at points of support, and at other points as may be necessary. including wiring in and to the heater.
28.11 Unless it has been determined that it is likely to remain in position during the handing of the heater prior to and during installation and after the heater has been installed, external thermal insulation (such as mats of woven glass fiber or mineral wool) is to be removed from the heater before it is installed in or on the surfaces of the test enclosure.
28.12 For the temperature tests, the heater is to be connected with wires sized as required for wire rated 75°C (167°F) except that, when the product is marked for use with a higher temperature in accordance with 46.10, wire of the temperature rating specified in the marking is used. The supply wires shall be sized in accordance with Table 310-16 of the National Electrical Code, ANSIINFPA 70. The correction factors from the table shall not be considered.
29 Power Input
29.1 The power anctor current input to a duct heater shall not be more than 105 percent of its marked rating.
29.2 To determine when a duct heater complies with the requirement in 29.1. the input is to be measured with the heater at normal operating temperature under full-load conditions and while connected to a supply circuit of rated voltage in accordance with 28.9. When a heater employs a nonmetallic element (such as carbon), the input is to be determined when the element is new.