Replacing a Light Switch and Changing the Wiring

How to Replace a Light Switch and Make the Wiring Connections, Identifying the Wiring, Connecting the Wiring for Your New Switch. How do I connect the wires when replacing my light switches? © By: Dave Rongey

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Wiring Light Switches
Electrical Question: How do I connect the wires when replacing my light switches?

I need to replace a single light switch, but when I pulled the old switch out of the wall here is what I discovered:

The switch has three wires attached to it, in addition to the grounding wire. Two of these wires are pushed into the back of the switch, the 3rd one is around one of the screws on the side. The new switch that I bought only has two screws, not counting the grounding screw. How do I connect this? I’m not sure if all three of the wires going into the old switch are “hot” or if only two are hot, which ones they are. What would that third wire be from? I also noticed on the old switch that it says “CU and CU Clad Wire only.” This means that I have copper wires, not aluminum, correct?

Thanks in advance for any help you can provide.
This home electrical wiring question came from: Dina, a Homeowner from Baltimore, Maryland.

Dave’s Reply:
Thanks for your electric wiring question Dina.

How to Replace a Light Switch and Make the Wiring Connections

Application: Wiring for a Light Switch.
Skill Level: Beginner to Intermediate – Best performed by a Licensed Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
Estimated Time: Depends on personal level experience and ability to work with tools.
Precaution: Identify the light circuit, turn it OFF and  Tag it with a Note before working with the wiring.
Notice: Installing additional electrical wiring should be done according to local and national electrical codes with a permit and be inspected.

Electrical Wiring for Light Switches

Identifying the Electrical Wires When Replacing a Light Switch

• The top portion of the switch where the one black wire is closest to the terminal for the bare ground wire should be the wire that leads to your light fixture.
• The two wires attached at the bottom portion of the switch should be a power source coming in and a power feed going out to other devices.

When Connecting the Wiring for Your New Switch, this is what I Recommend:

• Reconnect everything as it is, except the bottom two wires should be pig-tailed.
• This means that the two wires should be spliced together along with a third wire (the pigtail) which will be connected to the switch.
• A yellow or red wire nut can be used for this splice.
• If the length of the two wires is long enough, you can trim them shorter and use one of the cut wires for the pigtail.
• Attached the pigtail to the side of the bottom screw terminal of the switch.

Electrical Wiring Abbreviations and Terms about Light Switch Wiring

• AL is the abbreviation for Aluminum, and CU is the abbreviation for Copper, which are used to describe the compatibility or designation for electrical wiring and the  associated components.

More about Wiring Light Switches

Light Switch Wiring

• Wiring a Light Switch – Diagram 1
• Fully explained pictures and wiring diagrams about wiring light switches describing the most common switches starting with photo diagram 1.

Electrical wire

• Electrical Wire for the Home
• Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.