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Some spas and heated pools require a timer with a fireman switch. A fireman switch, sometimes called a heater protection mechanism, turns off the heater 5 to 20 minutes before the water pump turns off. This keeps the water circulating over the heat exchanger. The circulating water cools and extends the life of the heat exchanger. Three sets of wires connect to a timer with a fireman switch: one set from the circuit breaker, one set leads to the pump motor and one set leads to the heater.
Turn off the spa or pool's circuit breaker. Most outdoor spa and pools use a circuit breaker located in the main service panel, located next to the electric meter.
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Examine and understand the timer's wiring diagram or terminal chart, usually located on the inside of the timer's lid. The wiring diagram will identify the "Line," "Load," "Ground" and the "Fireman Switch" terminals.
Remove 3/8-inch of the insulation from each wire with wire strippers. Each wire set contains two hot wires and one ground, sometimes called earth. Most ground wires do not use insulation. Insulated ground wires either have green or green with a yellow stripe insulation.
Loosen the ground, line, load and fireman switch terminal screws with a slotted screwdriver. Do not remove the screws.
Wrap the ground wires around the ground screw, then tighten the screw with the slotted screwdriver.
Connect the wires from the circuit breaker to the timer's "Line" terminals, then tighten the terminal screws. If the spa or pool operates with 120 volts, push the black wire into the "Line 1" terminal and the white wire into the "Neutral" terminal. If the spa or pool operates on 240 volts, connect the black wire to "Line 1" terminal and the white wire to the "Line 2" terminal.
Connect the wires leading to the spa or pool's pump motor to the "Load" terminals, then tighten the terminal screws with the slotted screwdriver. If the pool or spa uses 120 volts, push the black wire into the "Load 1" terminal and the white wire into the "Neutral" terminal. Often the line and load's neutral wires connect to the same terminal. If the spa or pool uses 240 volts, push the black wire into the "Load 1" terminal and the white wire into the "Load 2" terminal.
Connect the spa or pool heater's wires to the fireman switch terminals. Push either heater wire into one of the fireman switch terminals and tighten the terminal screw. Push the second heater wire into the second fireman switch terminal and tighten the screw. Usually fireman switch terminals are interchangeable, unless the timer manufacturer's wiring diagram states otherwise.