Electrical Wall Switch Wiring

Throws and Poles

• Switches are identified by the number of throws, or positions, they have, as well as the number of poles, or terminals, in their construction. A simple on/off switch for a 120-volt circuit is a single-pole, single-throw switch, whereas one for a 240-volt circuit is a double-pole, single-throw switch. A three-way switch, which can be wired in tandem with a similar one to control lights from two locations is a double-throw switch. A dimmer includes an electronic means to modify voltage, such as a rheostat or a digital control, and can be considered a multiple-throw switch.

Switch Wiring Basics

• Variations in the design and functionality of wall switches notwithstanding, the wiring procedure for all of them is similar. Because a switch interrupts only the hot leg of the circuit, it has no terminals for the neutral, or return, leg. When you wire a switch, you connect the hot wire, or wires, coming from the power source to one terminal, or set of terminals, and the outgoing hot wires to the other set. The return wire bypasses the switch, so the incoming and outgoing return wires are typically spliced together. Switches, like all electrical devices, must be grounded for safety.

Wiring a Simple On/Off Light Switch

• Most residential light circuits are 120 volts and require a single-pole, single-throw switch. Such fixtures have two brass terminal screws positioned one above the other on one side. The hot circuit wire, which is black, can be attached to one or the other of these terminals, usually by loosening the screw and wrapping the exposed end of the wire around it. The hot wire leading to the lights attaches to the other terminal. The white return wires are twisted together and capped, and the ground wires are twisted together and attached to the green ground screw on the bottom of the switch.

Other Types of Switches

• The terminals for a dimmer switch are encased in the body of the device and connected to wires. Installing one is identical to installing a simple on/off switch, except that you have to twist these wires together with the circuit wires and cap them, rather than connecting the circuit wires to terminals. Three-way switches are always installed in pairs and have an extra terminal for connecting them together. Electricians use four-strand cable, which includes an red hot wire, for this purpose. Two hundred and forty-volt switches are double-pole, so they have four terminals and one ground. One terminal pair is for the incoming hot wires and the other for the outgoing wires.