How to Wire 110V for a Furnace | eHow Turn off the main circuit breaker in the service panel, remove the cover screws and open the panel. Move the switch on the new circuit breaker to the off position. Hook the back of the circuit breaker Remove a knock-out plug from the service panel with a screwdriver and pliers and insert a Strip 3/8 inch of insulation from the black and white cable wires. Install the bare ground on the See all full list on ehow What Is a Furnace Disconnect Switch? - The Spruce According to building codes, a furnace must be supplied by a dedicated circuit, meaning the circuit cannot supply power to anything other than the furnace. This circuit is served by its own circuit breaker in the breaker box (properly called the main service panel). The circuit wiring runs from the service panel to the disconnect switch, and from there to the furnace.