Photoelectric switches control the power to a connected appliance or fixture by measuring the light falling on the lens (also called the "eye"). These switches are mostly employed in outdoor locations to allow lights to turn on automatically after the sun has gone down. Wiring a photoelectric switch, whether it's on its own or into a light fixture, first requires that you shut off the power supply for the circuit so you can work safely.
Disconnect the power for the circuit in which you are installing the switch. Locate the main circuit breaker for your house or apartment. Find the circuit where you are installing the switch. There should be labels or a guide on the inside of the breaker telling you which switch controls what circuit. Flip the switch for your circuit to the "Off" or "0" position.
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Go to the location where you are wiring the photoelectric switch. Locate the power wires for the switch installation. There will be two: one black (hot) and one white (neutral). Touch each of these with the terminals from the voltmeter. It should read "0" or no voltage before you begin work. If it is still live, try turning off a different circuit at the main breaker.
Disconnect the wiring from the light if it is already mounted. Remove the light cover. Loosen the terminals on the light and remove the white and black wires.
Wire the photoelectric switch. To connect a photoelectric switch to a light, for example, begin by connecting all three of the white cables (white neutral cable from house supply, white cable on light, white cable on photoelectric switch) and tying them together with a wire nut. Use the electrical tape to secure the nut in position by wrapping the tape around the base of the nut and continuing to wrap it around the wires. Connect the black cable from the house to the black cable on the photoelectric switch with a wire nut and tape. The red wire on the photoelectric switch should be connect to the black wire on the light. Twist and secure with the tape and wire nut as with the white and black wires.
Mount the photoelectric switch, if needed. Some light fixtures provide a mounting hole for the photoelectric switch. Insert the eye of the switch into the hole and secure with a wing nut or whatever type of nut is supplied.
Replace the lighting switch cover.
Restore power to the circuit. Test the photoelectric switch by taping a black piece of cardboard or poster board over the eye. If the light doesn't turn off, cut the power to the circuit. Go back and check your work, tightening any connections as necessary.