UL 521:2019 pdf download.Heat Detectors for Fire Protective Signaling Systems.
11.5 ln a heat detector of the normally open-contact type, a separate terminal screw shall be provided foreach incoming and outgoing wire.
COMPONENTS-ELECTRICAL
12 General
12 General
12.1 Insulating material
12.1.1 Material for the support of live parts shall be nonflammable and moisture-resistant insulatingmaterial such as porcelain, phenolic or cold-molded composition, or other material determined to complywith requirements for the support of live parts.
12.1.2 The insulation of coil windings of relays, transformers, and the like shall resist the absorption ofmoisture.
12.2current-carrying parts
12.2.1 Acurrent-carrying part shall be of a non-ferrous metal such as silver, copper, or copper alloy.12.2.2 Electrical parts of a heat detector rated more than 30 volts shall be located or enclosed so as toreduce the risk of unintentional contact with uninsulated live parts.
12.2.3 Live screwheads or nuts on the underside of an insulating base intended for surface mountingshall be countersunk not less than 1/8 inch(3.2 mm) and shall be covered with a sealing compound.
Exception: If such parts are staked, upset, or prevented from loosening by an equivalent means, they maybe insulated from the mounting surface by material other than sealing compound.
13Contacts
13.1 A heat detector having normally closed contacts and intended for fire alarm service shall be capableof being used in conjunction with a system control unit, transmitter, or similar system component by whichits alarm operation is indicated, so that an open-circuit fault in the heat detector circuit will not result in analarm signal. This does not apply to heat detectors employed for releasing-device service where openingof the circuit results in operation of the releasing device, as in the case of fire doors and dampers.
13.2 lf the heat detector operates by making contact (not by fusing) between metal parts, there shall be awiping, scraping.,or spring action between the parts unless the contact is made in a tightly closed housingthat will prevent fouling by dust.
