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How do you add a separate light switch?


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2015-07-15 18:28:51
2015-07-15 18:28:51
for USA, Canada and countries running a 60 Hz supply service.

1. On a 120 volt system in which the house is located in the United States, how do I wire a light switch that only has one point which will control the device?

A: (TURN OFF THE CIRCUIT FIRST) In order to wire this switch, we'll assume you are not running a completely new circuit, instead you are tapping off of a nearby receptacle or other power supply.

With Romex cable, inside the box where the switch is or will be, optimally you should have all black, all white and all copper individual wires. The neutral (white), you want to wire nut all of them together and bury them in the back of the box.

Second, you want to do the same with the grounds (complete copper or green wires) with the exception of this: You have to check what type of box it is in which the switch has been or will be placed.

1. If it is a metal box then you will need two ends (or very small pieces of same colored wire) coming out of your grounds wire nut. These are called pig tails. One end will go from wire nut to switch. The other wire end will be attached to the metal box via a green ground screw.

2. If the box is a non metal, plastic box, then everything is the same with the exception that instead of two wire ends coming from your grounds' wire nut, there will only be one end that will emerge. Take this end and screw it onto your switch itself where the dedicated ground screw is located on that switch. Usually it is a green screw on the switch itself. That's the spot where you will land the end of your ground wire.

Now that the grounded and grounding conductors (Grounds and neutrals) are finished, we are left with the task of your hot conductor and the switched leg (the screws on the switch itself are usually gold colored screws), unless your box has more than two Romex cables entering it. Then, you have to take a volt meter and determine which wire is the constant hot. In the case of the wire going toward the light, make sure if you are the one who ran the wire from switch to device, you have the black wire (switch leg) marked. If not, you have opened up a can of worms.

When multiple wires are entering a box, the most important wire to separate from all the other black wires is your switched leg. Your other black wires are (90% of the time) loads and one feed. Wire nut the feed and loads all together with a 6" pig tail coming out of your wire nut going toward one of the two screws dedicated for hot conductors. Land your feed (6"pig tail you just made) on one of these screws and your wire headed to/from your device (I have been assuming it is a light) on the other. You're done.

In summation:

Turn off the circuit which is responsible for powering the switch (or proposed switch).

Wire nut all white wires with no pig tails.

Determine if your box is metallic or plastic.

Cut one or two 6 inch pieces of wire colored green or bare copper.

Grab the (those) cut piece(s) and all the grounds in the box.

Wire nut them together where you will have one or two small pieces of wire coming from where the wire nut is at. (The wire nut that connects all your grounds.)

Land the 6" piece(s) in its (their) appropriate place(s) as described above.

Land one black wire (or hot conductor) on one of the gold screws.

Twist screw with wire underneath tightly.

Repeat the previous two steps with your other black wire remaining.

Turn on the circuit which controls the switch you were working on.

Enjoy controlling the device that prior to you working on it, had power continuously.

Please take extreme caution when working with electricity, as it can kill you. All it takes is 5 milliamp and you could die. If you feel for any reason that you or others may be hurt off of this project, then by all means contact a licensed electrician.


As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.





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Only if the existing switch box has an unswitched hot and neutral in it.

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