Figuring out 3-way dimmer switch wiring is one of the first steps of any DIY project. Installing a dimmer with any light fixture has multiple benefits. After installing a three-way dimmer switch, you’ll economize on power bills and get the right amount of brightness you need at a given time. Improving the room’s ambiance and the longevity of your bulbs are only some of the added positives.
Before you get started, remember to try a DIY project only if you have some experience in doing electrical work. If you haven’t done this before, consider calling an expert professional to take care of your wiring. But if you’re sure you can handle it, here’s how to get started.
Some Safety Precautions for 3-Way Dimmer Switch Wiring
When you’re ready to install a three-way dimmer switch, start with these safety precautions:
- We strongly recommend purchasing a multimeter and learning how to use it before going any further; they are not expensive and are a must-have for carrying out electrical work safely. Please read the general instructions on its use, then thoroughly read the measuring AC Voltage (Alternating Current Voltage) section. Be sure you understand how to select the correct voltage range; AC Voltage is what you will be testing.
- Check that you have the correct switch that you will be installing your dimmer to control its associated light or lights. A bulb or appliance test is simply a quick way to check that you have the correct switch and whether there is power to that circuit. It is imperative to understand that a light bulb that is not glowing or an appliance that is not functioning DOES NOT GUARANTEE THAT THERE IS NO ELECTRICITY AT THAT DEVICES ON/OFF SWITCH OR WALL RECEPTACLE simply because that bulb or appliance may be faulty.
- Turn on the light switch you’re going to replace with a smart device; the light/s should come on as normal; if so, there is obviously power to the light bulb/s. If the bulb/s are the smart type with a remote control, you may need to activate it to make the bulb light up. If the light/s do not come on or there is no light bulb/s in the socket/s, insert known working bulb/s or carry on to 4.
- Remove the outer covering from the switch if it has one; modern switches can have clip-on coverings that are easily removed generally by prying with a flathead screwdriver. DO NOT TOUCH any exposed copper wire or other metal parts of the switch. Remove the necessary screws from the switch plate, and carefully lift the switch plate away from the housing, exposing the wiring going into the switch itself.
- You MUST identify the true function of each wire attached to the light switch with your multimeter. Again DO NOT TOUCH any exposed copper wire or other metal parts of the switch at this stage; treat all wires as live until they are proven otherwise. Black wires are normally HOT (Live), Red are also normally HOT (Live), White is normally NEUTRAL (Common), and Green or Bare copper wire is normally GROUND (Earth). We usually say this because it is not uncommon for the wire colors to be incorrectly used, which is both bad practice and dangerous!! You will often see a piece of colored tape or tube around wires representing the color the wire should be, and there should be matching tape or tube on the other end; note the use of the word should!
- Ok, now you do some testing; with your multimeter set to measure AC Volts (Alternating Current Voltage). Put the black multimeter probe tip on the switch’s neutral wire terminal and the red probe on the ground wire terminal; there should be 0v (voltage) displayed. Leave the black probe on neutral and move the red probe to the “other” wire going into the switch; you will get a reading of approximately 120v when electricity is supplied to that circuit.
- Now go to the building’s main electrical panel, locate the breaker switch for the lighting circuit you are working on, and switch it off. Safety first!! – put a note on the panel indicating that the switch must remain off as someone is working on the circuit. Also, putting some tape across the breaker switch warns that someone may be working on that circuit.
- Go back to your worksite to check if the light/lights are now off; if they are off, you can be confident but not yet certain there is now no power to that circuit, do the same multimeter test performed earlier to confirm all wires have no voltage on them. If the light/s are still on, the wrong breaker was switched off; repeat step 7.
- If your test shows 0v on all terminals, it is safe to proceed with replacing the existing switch with your smart device. If you can’t identify the hot, neutral, and ground wires, or you are unsure about any readings from your multimeter, we advise you to contact an electrician to come by and complete the task for you.
With these safety precautions taken, you are ready to begin working on the three-way dimmer switch installation.
How do I know if I have a 2-way or 3-way switch?
If your light fixture is connected to a single switch for turning on and off, that’s a two-way switch. You can also call it a single-pole switch. However, if you have two switches controlling a single or multiple light fixtures, that’s a 3-way switch.
If you wish to install a dimmer, be sure to get a device designed for 3-way dimmer switch wiring for proper installation.
Remember that you can only install a single device to control the brightness when installing the dimmer. You cannot have two dimmers for a single set of light fixtures. While your dimmer can also have an off-and-on button, the other switch must be a standard on-off switch.
Before buying the appropriate dimmer, you’ll also check for the total wattage the switch will handle. To do that, make a list of the light fixtures the switch will be controlling, then add together the maximum wattage for each.
For instance, if the total is 600 or 800 Watts, you must get a dimmer compatible with this number. Getting a higher wattage controller is always preferable. Anything less than that risks overheating or a fire. Also, get a dimmer switch that matches the kind of bulbs you have, like incandescent, halogen, CFL, or LED.
Do you need special wiring for a dimmer switch?
Most dimmer switches use a 12/2 wire with three cables that connect to the light fixture. They also have a 12/3 wire with four cables that run between the dimmer and the on-off switch. Newer brands come with a green grounding wire or a green screw. This green screw is where you’ll connect the grounding wire from the switch housing. Chances are that the wall has bare copper wires as ground; you must connect the ground wire to the 3-way dimmer switch. Here’s a quick overview of the typical wire colors and how to use them.
- White wires are neutral wires.
- Grounding wires can be green, brown, or bare copper.
- Black wires are hot wires.
- Red wires are hot wires.
- Traveler wires can, in reality, be any color.
Understand that 3-way dimmer switch wiring running from the light fixture to the dimmer will likely have three cables. They are a copper grounding wire, a hotwire, and a neutral wire. The same goes for the wires connecting the power source to the on-off switch.
However, the dimmer and regular switch cables typically have neutral, grounding, and two traveler wires. Check out the 3-way switch with dimmer wiring diagram below to understand how it works.
How to attach the wiring for the 3-way dimmer switch
Examine the dimmer you’ve purchased. Some devices have wires that must attach to the corresponding wiring in the wall socket. Others come with terminals and screws. First, you’ll connect the ends of the wires in the wall with the appropriate terminals on the dimmer. Next, you’ll screw them securely in place. Read ahead for some step-by-step directions:
Procedure for connecting the 3-way dimmer switch wiring
- Start by sorting the wires in the wall socket. You will set two sets of cables, one from the light fixture and the other running from the on-off switch.
- Examine each wire and ensure that a ⅝” section is bare. If needed, use the wire stripper to remove a section of the plastic covering.
- Whether you’re replacing an old dimmer or installing a new one, start by identifying the grounding wires. Using a copper crimping sleeve, connect the grounding wires together. Clip off the end of one of the wires, leaving you with a single grounding wire.
- Identify the neutral wires and connect them by twisting them, then use a wire nut to hold them together securely. Push these wires back into the housing; you won’t need them again.
- You’re now left with two traveler wires, one hot wire, and one copper grounding wire.
- Examine your dimmer switch. It will either have wires you can connect with the proper wires from the wall socket, or the dimmer will have terminals with screws. Some dimmers are designed to have the cables looped around the screw and tightened. Others have a small gap below the screw. You must insert the ends of the wires under the screw, then tighten the screw to hold them in place.
- Depending on the dimmer switch design, curve the ends of the wires to create tight loops. Or, trim the wire’s insulation to ensure that only exposed copper wire fits under the screw entirely. Make sure there aren’t any loose ends that might touch and create a short circuit.
- Typically, the traveler wires attach to the bottom two terminals on either side of the dimmer switch. The remaining grounding and hot wire connect with the terminals on the dimmer top.
Completing the 3-way dimmer switch circuit
Now that the 3-way dimmer switch wiring circuit is complete, check that the wires are securely fixed. Replace the dimmer switch into the wall socket and screw it in place. You might want to go back to the circuit box and restore the power.
Before affixing the faceplate, test the dimmer for proper functionality. Now that you know how to handle the installation, let’s address some FAQs you might have.
Frequently Asked Questions – FAQs
You can have a maximum of 1 dimmer for every set of light fixtures controlled by a single on-off switch.
Yes, you can make it work. Most 3-way switches are single pole double throw or (SPDT) having 3 screw terminals. You can safely attach them to a single-pole wiring circuit.
Several reasons can result in the dimmer switch not working. The primary cause can be that the 3-way dimmer switch wiring is not installed correctly in the appropriate terminals. You might also want to check if you turned on the power. If nothing works, contact an electrician. Or check the troubleshooting tips in the user manual that comes with the dimmer switch.
Yes, you can install a 3-way dimmer switch in a 4-way circuit. But make sure to check that the voltage and amperage of the dimmer are compatible with the circuit.
A 3-way switch has three terminals and controls lighting from two locations. However, the four-way switch has four terminals and controls the room lights from two or three spots.
While this guide gives you an overview of how 3-way dimmer switch wiring works, remember that circuits sometimes vary. You might open the wall socket and find unfamiliar wires, or the dimmer might not work as expected. If that happens, call a professional electrician to deal with the installation. Since you’re dealing with electricity, exercise extreme caution.