How do I Wire a 120V Indicator Lamp?
Indicator lamps exist to tell you whether something is either on or has power going to it. When you deal with 120 volts AC, all outlets built into houses since the 1950s are polarized and have a "hot" leg and a neutral leg. The energized "hot" leg is the narrow blade on polarized plugs. Some plugs are not polarized and have two narrow blades. In-line switches and wall switches always interrupt the hot leg when turned off, if they are wired correctly. The best place to connect an indicator light is between the switched side of hot and neutral.
Use a commonly available neon induction probe to test the AC source for which you will install an indicator light. Test which leg is actually wired "hot" (the probe will light), and make a note.
Unplug the device you are wiring with the indicator, or if you're working with a hard-wired connection like a wall switch, turn off the breaker or take out the fuse for the circuit.
Cut the hot-side wire between the switch and the device you are powering. Strip back 3/4-inch of insulation on both sides of the cut. The indicator light fixture usually comes wired with stripped ends, but if not, strip those, as well. Wire-nut the cut ends together with one indicator wire.
Repeat Step 3 with the neutral return wire and the other indicator lead. If you are wiring the indicator to a wall switch, wire one wire end under the neutral wire screw and the other under the switched-side screw, along with the wires that are already there.
Flip the circuit breaker on or reinsert the fuse. Test the indicator by flipping on the switch. If it does not light, try changing the bulb. When everything works, mount your indicator light in place.
- If your indicator light is a modular block pilot light, it will have terminal screws. Just use a short length of zip cord stripped at each end for each screw, and tighten down the screw over one end looped around the screw.
- Some lights have flat tabs with holes in them. Solder short lengths of insulated wire, ends stripped, to the tabs to make it a wired fixture: insert wire through the tab hole and bend around it. Touch hot iron to the tab and wire until solder touched to both melts and flows into it. Remove solder and iron.
Jan Benschop started writing professionally in 1979. His corporate technical writing clients included Nortel, Alcatel and Glaxo. Also the author of several short stories, Benschop holds a Bachelor of Science in English from Campbell University. He built loudspeakers for more than a decade and has several international patents pending in the field.
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