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If an auxiliary drain pan cannot be installed under units containing cooling coils, a drain pipe shall be connected to the secondary drain (overflow) connection so that the overflowing condensate resulting from flow restrictions in the primary drain pipe will be carried away without damaging the unit and its surroundings. The overflowing condensate shall be drained to a conspicuous point and serve as an alarm which indicates that the primary drain pipe is restricted. As an alternative, overflowing condensate shall be piped to a secondary drain pan, firmly secured and located along the side of the cooling unit, from which the condensate will be drained to a conspicuous point. A secondary drain pan shall have a capacity of not less than the capacity of the condensate drain pan, shall be not less than 1 1/2 inches (38 mm) deep, and shall be constructed of not less than 0.0276-inch (0.7 mm) thick galvanized sheet metal. As an alternative to a separate drain line, a UL-listed water level detector or float switch device shall be used to control overflow by automatically shutting down the equipment or appliance that produces the condensate.