Wiring a Middle-of-Run Single-Pole Switch

A switch controls the flow of power in an electrical circuit. It provides an open circuit in the off position and it acts as a short circuit in the open position. A switch that has two screw terminals is a single-pole switch and it controls a circuit from one location only. Most residential switches are single-pole. Power is connected to one side of the switch at all times. When the switch is on, electricity flows from the wire attached to the powered screw terminal, through the switch, and into the load wiring connected to the other screw terminal. If the switch is at the end of a circuit, power will flow through the black wire and return through the white wire, which is actually the continuation of the hot leg and is taped black to classify it as hot. (With the switch in the on position, either wire can cause an electric shock.) If the switch is in the middle of a run, the switch still acts as an interrupt of the flow of electricity through the hot leg. Both hot black wires will connect to the switch and the two white neutral wires are spliced together with a wire connector in the switch box. The bare copper wires splice together, and then pigtail to the green grounding screw on the switch and also to the box if the box is metal.

It is not a difficult job to replace or add a single-pole switch. The process may vary slightly, depending on your wiring and whether or not the switch is grounded. A grounded switch has an extra terminal screw at the base that is green or shows the letters GR. This redundant grounding system is more reliable than systems that don't connect the ground to the switch. If wires are encased in metal conduit, the conduit is usually grounded, but not always. Before starting work, turn off electrical power to the circuit for the switch being installed.

Loop each wire in a clockwise direction around either screw terminal so that the loop will tighten in the direction of the screw. In a middle-of-run switch circuit, splice the white neutral wires together inside the switch box. (Fig. 2)