How to Install an Electronic Dimmer Switch

  • 01 of 10

    Installing an Electronic Dimmer - Introduction

    Installing light dimmer
    Michellegibson / Getty Images

    Basics

    Standard wall switches control power to light fixtures on a simple on-off  basis. However, dimmers allow you to vary the lighting intensity by controlling the amount of voltage a fixture receives. 

    Old-style dimmers operated using a rheostat—a large variable resistor. As you increased resistance in the rheostat, the voltage to the lamp was decreased and the energy that would have gone to  brighter light instead wound up as wasted heat energy dissipated in the dimmer.

    But times have changed, and now we use electronic dimmers. Electronic dimmers now use an ingenious little device called a Triac. A TRIAC is a three terminal, solid state electronic switch or relay that quickly turns power to a lamp on and off up to 120 times per second. Since this power sequencing occurs so fast, it is not perceptible to the naked eye. Other benefits are that it generates very little heat and saves energy

    Getting Started

    So read on! This tutorial walks you through the steps of replacing a single-pole switch with an electronic dimmer using incandescent or halogen lighting. You can do it easily, create mood lighting and save energy in one easy project. If you have a three-way switch configuration, in which the light fixture is controlled by two switches, then you can install a dimmer to replace one of the switches, but make sure to buy a switch identified as a three-way dimmer. 

    NOTE: If you have a standard compact fluorescent bulb (CFL) or LED bulb,  then dimmer switches will not work. If you want to dim a CFL or LED  bulb, you will need a special dimmable bulb, which costs more than standard bulbs. 

    Difficulty Level

    • Easy

    Needed Tools and Materials

    • Screwdriver
    • Neon Circuit Tester
    • Combination tool
    • New electronic dimmer switch
    • Wire nuts
    • Electrical tape
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  • 02 of 10

    Turn Off Power to Circuit

    circuit breaker
    Turn off power to switch before starting installation. © 2009 Home-Cost.com

    First things first. Before any repair is performed on an electrical circuit you need to make sure the power is off.

    • Turn off power to the circuit feeding the switch. You do this by going to your electrical service panel and either removing the fuse or turning off the circuit breaker feeding power to the switch.
    • Remove the cover plate on the switch you are replacing, and carefully pull the switch from the electrical box by pulling gently on its mounting straps. 
    • Using a Neon Circuit Tester, test the switch terminals to see if power has been shut off. Touch one probe of the circuit tester to each of the screw terminals on the switch, while touching the other probe to either the bare copper grounding wire or the grounded metal electrical box. If the tester does not light up, the power is off. 
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  • 03 of 10

    Disconnect and Remove Existing Switch

    Dimmer preparation
    Disconnect existing switch and prepare the wires. © 2009 Home-Cost.com

    Now that the power is off you can safely remove the old switch.

    • Loosen the screw terminals on the switch and remove the wires. If the switch has been connected with push in fittings, there will be a slot to insert a small screwdriver or nail that will release the wire. 
    • Straighten the wires and check on their condition. Badly nicked wires will need to be clipped off and re-stripped to provide bare wire to connect to the dimmer switch.
    • There will usually be two or three wires to disconnect from the switch. One will usually be an insulated black wire and is a "hot" wire. Another insulated wire may be white, but with black electrical tape wrapped around it to indicate it, too, is carrying hot current in this situation. The third wire, if present, will be a bare copper ground wire. If there is no bare copper ground wire on your switch or in your electrical box, read on. 

     

     

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  • 04 of 10

    What If Your Switch Box Has No Grounding Wire?

    Dimmer
    Where switch box has no ground wire the dimmer ground wire should be capped off. © 2009 Home-Cost.com

     

    Sometimes in an older home or apartment, you may have a switch box that has no ground wire. In that case, an exception in article 404.9(B) of the current National Electric Code (NEC) allows a dimmer without a connecting ground wire to still be installed if it is a replacement. NOTE: this information is based on the 2014 NEC. The NEC is revised every three years, so it is possible this exception may change with later code updates. 

    Simply remove the dimmer wire, or cut it short and cap it with a wire nut as shown in the photo above. Also note that if the dimmer is installed without a ground wire as under this NEC exception, then it needs to have a plastic, noncombustible wall plate.

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  • 05 of 10

    Connect Ground Wire to Dimmer

    Dimmer Ground Wire
    Install dimmer ground wire to ground wire in switch box. © 2009 Home-Cost.com

    Assuming you have a ground wire in your switch box it's time to connect it.

    • If there is insulation on the dimmer lead for the ground wire, strip away about 5/8" of wire,  using a combination tool. 
    • Hold the dimmer ground wire alongside the circuit ground wire and fasten the together with a wire nut twisted over the ends in a clockwise direction. 
    • Securing the connector with a couple of wraps of electrical tape is a good idea but not required.
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  • 06 of 10

    Connect Load Wire to Dimmer

    Dimmer Load Wire
    Install dimmer LOAD wire. © 2009 Home-Cost.com

    Electronic dimmers can get a little particular about which wire goes where.  You'll likely notice two different colored wires on the back of your dimmer. One wire will be black and the other will be a color, probably red or blue. Let's assume blue for this tutorial.

    This blue colored wire is to be connected to the LOAD wire in your switch box. The load wire runs from the switch to the light fixture.

    Now how do you tell which wire is which? As you recall, one of the insulated wires you disconnected from the original switch was black, with the other wire, white, hopefully, tagged with black tape. This white wire is the LOAD wire. The black tape means the previous installer marked it to indicate it is not a neutral wire  but is also carrying hot current.

    Connect the blue wire to LOAD wire as follows:

    • If there is pre-cut insulation on the dimmer lead for the blue wire, remove it so you expose about 5/8" of wire.
    • Hold the exposed end of the dimmer blue wire alongside the circuit LOAD wire and fasten them together with a wire nut twisted over the ends clockwise.
    • Turn the pair of wires until there is a slight twist in them both—then the connection is tight enough.
    • Securing the connector with a couple of wraps of electrical tape is a good idea but not required.
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  • 07 of 10

    Connect Hot Wire to Dimmer

    Dimmer Hot Wire
    Install dimmer Hot wire. © 2009 Home-Cost.com

    Next, you connect the remaining black wire, which is the HOT wire. The hot wire provides power to the circuit and runs from the switch to the source of electrical power in your panel. 

    Connect the black wire lead from the dimmer to the solid black wire in the switch box as follows:

    • If there is pre-cut insulation on the dimmer lead for the blue wire, remove it so you expose about 5/8" of wire.
    • Hold the exposed end of the dimmer blue wire alongside the circuit HOT wire and fasten them together with a wire nut twisted over the ends clockwise.
    • Turn the pair of wires until there is a slight twist in them both—then the connection is tight enough.
    • Securing the connector with a couple of wraps of electrical tape is a good idea but not required.
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  • 08 of 10

    Test Dimmer for Proper Operation

    Test Dimmer Operation
    Turn circuit back on and test operation of dimmer. © 2009 Home-Cost.com

    Now that the wires are connected, we need to test the operation of the dimmer as follows:

    • Turn the power back on at the electrical service panel.
    • Some dimmers such as this Leviton Decora© have an air gap switch which locally controls power to the switch. When pulled out it cuts power, and when pushed in it allows power to the switch. Make sure it is pushed in.
    • Press the touch plate, lever or slide bar to turn the dimmer on.
    • If the lights turn on, you are all set to go to the next step.
    • If the dimmer does not work,  see Section 10: "Troubleshooting" in this tutorial.
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  • 09 of 10

    Install Dimmer Coverplate

    Dimmer cover plate
    Install dimmer cover plate. © 2009 Home-Cost.com

    Now that you have the dimmer all wired up and working, you need to put it back in the wall and cover it up.

    • Carefully fold the wires back into the switch box.
    • Press the dimmer assembly into the switch box.
    • Install the two dimmer plate mounting screws.
    • Place the plastic cover plate over the dimmer and fasten in place with the two finish screws.

    That's it, you're done!

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  • 10 of 10

    Dimmer Troubleshooting

    Man adjusting light dimmer
    Tetra Images / Getty Images


    Troubleshooting

    If you hooked up the dimmer and it's not working correctly,  let's take a look at some possible problems and solutions:

    Dimmer does not work

    • The black and blue dimmer wires may be miswired. Try reversing the wiring of the black and blue wires to the circuit wires. 
    • The air gap switch may be  pulled out,  shutting off switch. Make sure the air gap switch is pushed in. 
    • The bulb may be burned out. Replace a bad bulb.
    • The circuit breaker may be tripped or the fuse burned out. Reset the breaker.
    • The fixture may use a CFL or LED bulb that is not dimmable. Use correct bulb. 

    Lights Flicker

    • Bulb power is less than 40 watts. Replace with a larger bulb. 
    • Loose wire connection(s) in the switch box. Check wires. 
    • Bad fixture bulb connection. Tighten bulb in the socket.