How to Expertly Install a 3-Way Dimmer Switch

The installation of a 3-way dimmer switch offers both functionality and convenience. Often misunderstood as two-way switches, these 3-way switches are integral in controlling lighting from multiple locations – a feature especially beneficial in large rooms or extended hallways. This guide delves into the nuances of selecting and installing the right 3-way dimmer switch.

We’ll explore how to determine the appropriate size of the dimmer switch based on your lighting fixtures’ maximum wattage, emphasize the importance of adhering to safety standards, and touch on the cost-effective advantages of opting for a single-location dimmer installation.

Whether you’re an experienced DIY enthusiast or a homeowner looking to understand more about your home’s electrical system, this comprehensive guide will equip you with the knowledge needed for a successful installation.

Understanding 3-Way Switches and Their Functionality

When it comes to managing the lighting in your home, a 3-way dimmer switch is an excellent tool. Contrary to some misconceptions, they are called 3-way switches, not two-way.

3-Way Switches

These switches are designed to control an electrical device, such as lights, from two or more locations. They are particularly useful in large rooms or long hallways, where multiple switch locations are desirable for convenience.

Choosing the Right Dimmer Switch for Your Home

The key to successful DIY dimmer switch installation starts with selecting the appropriate switch. The Lutron Ariadni AY-603P, a 600-watt, preset, incandescent dimmer, is popular for its efficiency and reliability.

But how do you determine the right size for your needs?

It’s a matter of calculating the maximum wattage of the fixtures controlled by the switch. If, for instance, you have six 65-watt lamps, you might think a 390-watt (6 x 65 watts) dimmer would suffice.

However, the correct approach is to consider the maximum wattage your fixtures can handle, which is often higher. If your recessed cans allow up to 75 watts each, you’ll need a dimmer switch to handle at least 450 (6 x 75 watts).

Adhering to Maximum Wattage Ratings

One common oversight in home electrical systems is exceeding the fixture’s maximum wattage rating. This is not just a technicality but a critical safety issue.

Overloading a fixture can lead to excessive heat buildup, posing a significant fire hazard. It’s essential to match the wattage of your bulbs to what your fixtures are rated for. If a fixture is rated for 60 watts, using a 100-watt bulb is not just inadvisable; it’s dangerous.

Opting for Single Location Dimmer Control

While some homeowners might prefer a master and slave switch system, like the Lutron Maestro, for dimming lights from multiple locations, others opt for a simpler, single-location dimmer switch. This choice can be not only a matter of preference but also cost-effective.

Installing a single dimmer switch is typically less expensive than a more complex master and slave setup in terms of labor and materials.

3-Way Dimmer Switch: Step-by-Step Installation Guide

You’ll need a few tools: a screwdriver, wire strippers, a voltage tester, and the new 3-way dimmer switch. Most importantly, safety comes first. Always start by turning off the power to your working circuit.

  1. Turn Off the Power: Locate your breaker box and switch off the power to the circuit where you’re installing the dimmer.
  2. Remove the Switch Cover Plate: Unscrew and remove the cover plate of the existing switch.
  3. Remove the 3-Way Switch: Unscrew the switch from the electrical box and gently pull it out.
  4. Disconnect the Wires: Pay special attention to the wire connected to the common terminal (usually marked by an odd-colored screw). This wire must connect to the common terminal on the new dimmer switch. Disconnect this wire last and immediately connect it to the new switch.
  5. Connect the Wires: Attach the common wire to the common terminal on the new dimmer switch. Also, ensure you connect the ground wire. Proper grounding is crucial for safety.
  6. Install the 3-Way Dimmer Switch: Secure the new dimmer switch in the electrical box and ensure all connections are tight.
  7. Install the Switch Cover Plate: Reinstall the cover plate once the switch is in place.
  8. Test the Installation: Turn the power back on and test the switch. Activate the light from one switch, then use the other switch to turn it off, and vice versa. If the light operates as expected, your installation is successful. If not, the most common issue is the incorrect placement of the common wire.

If the switch isn’t working correctly, the first thing to check is the connection of the common wire. Ensure it’s securely attached to the common terminal on the dimmer.

How to Re-wire the Circuit for a 3-Way Dimmer Switch

When installing a 3-way dimmer switch, correctly wiring the circuit is crucial for the switch to function properly. Here’s a step-by-step guide on how to wire your circuit:

  1. Identifying the Wires:
    • First, take note of the Black and Red wires coming from the same slot on the back of the dimmer.
  2. Connecting the Black Wire:
    • The Black wire on the dimmer should be connected to the Black wire that leads to the light fixture(s).
  3. Connecting the First Red Wire:
    • The Red wire on the dimmer is to be connected to the Red wire that goes out to the other switch.
  4. Handling the Second Red Wire:
    • The other Red wire on the dimmer, located in the same slot as the Green ground wire, should be connected to the WHITE wire going to the other switch. This white wire becomes “hot,” so mark it as black with a piece of electrical tape for identification.
  5. Connecting the Green Ground Wires:
    • All the Green ground wires in the box should be connected together.
  6. Wiring the Other Switch:
    • For the other switch in the 3-way setup:
      • The Black wire connects to the brass screw.
      • The Red wire attaches to the silver screw on the same side as the Black wire.
      • The White wire, now identified as Black, connects to the other silver screw on the opposite side of the switch.
      • The bare ground wire is connected to the green screw on the switch.
  7. Wiring the Light Fixture(s):
    • Wiring the light fixture(s) should be straightforward and typically follows standard wiring practices.

Remember, ensuring that each wire is correctly identified and connected is essential for the 3-way dimmer switch to function properly. If you’re unsure, it’s best to consult with or hire a professional electrician. Safety should always be your top priority.

Installing a 3-way dimmer switch is a practical and beneficial upgrade for any home lighting system. By understanding the type of switch you need, calculating the correct wattage, and adhering to safety standards, you can enhance the functionality and ambiance of your home’s lighting. Remember, accuracy and safety are paramount in any electrical installation. Consulting a professional electrician is always wise if you’re ever in doubt.

Mas Broto

Written by: Mas Broto

Mas Broto is a small business owner with 30 years experience in the real estate industry. He is the founder and editor of, the most comprehensive free home improvement website on the planet!