How to Install a Reed Switch

Many people operate a reed switch everyday without even knowing it. Residential alarm systems use reed switches to detect an open door or window. A reed switch consists of two parts, a stationary switch and movable magnet. An alarm system's stationary reed switch mounts to the window casing or door jam and the movable magnet mounts to the door or window. A plastic housing covers both parts. When the door or window closes the magnet pulls on the switch's internal "reeds." As the magnet moves away from the switch, the reeds close and the alarm trips.

• 1

  Identify the wire terminals on the switch portion of the reed switch. A label, printed on the switch's housing near the terminal screws, identifies each terminal's function. The terminal with the "Com" label connects to the common wire. The "NC" label stands for "Normally Closed" and the "NO" label stands for "Normally Open."

• 2

  Inspect the wiring diagram of the device that the reed switch operates, usually the alarm's control panel, to determine if the reed switch should operate as normally open or normally closed. The wiring diagram, usually found on the device's housing, will show either a "NO" or "NC" at the switch location. Most residential alarm systems use normally closed reed switches.

• 3

  Remove one-half inch of the insulation from both wires that the reed switch connects to with wire strippers. Two wires connect to the stationary portion of the reed switch.

• 4

  Wrap one of the wires around the reed switch's "Com" terminal screw. Tighten the screw with a Phillips-head screwdriver.

• 5

  Wrap the second wire around either the reed switch's "NC" or "NO" terminal screw and tighten the screw with a Phillips-head screwdriver. If the device's wiring diagram identifies the reed switch as "NC," then connect the wire to the "NC" terminal. If the device's wiring diagram identifies the reed switch as "NO," then connect the wire to the reed switch's "NO" terminal.

• 6

  Secure the stationary portion of the reed switch to a solid surface, usually a door or window frame, with the manufacturer supplied screws. Position the switch so that it rests near, but not touching, the movable object that the magnet portion of the reed switch attaches to.

• 7

  Secure the reed switch's magnet to the movable object, usually a door or window, with the manufacturer supplied screws. Position the magnet so that it mounts close to, but not touching, the stationary portion of the reed switch.