How to Install a Double Pole Switch

Lead Image
  • 2-4 hours
  • Intermediate
  • 25-75
What You'll Need
Double pole switch
Electrical device box
Wire connectors
Wire stripper or utility knife
Black electrical tape
Slotted screwdriver
Multimeter
Insulated gloves

When setting up stationary appliances or equipment, it's always a good idea to establish an accessible disconnect nearby from which the power can be easily turned off. That way, if an emergency occurs, like a component catching fire or just smelling burnt, the power can be quickly shut down, eliminating the risk of further damage. Such a switch can also provide immediate electrical access if required.

If a hookup is running on 110 Volts, a single pole switch is adequate to cut off the only hot line feeding it. If the hookup is 220 volts however, the feed will consist of two hot lines besides the neutral to power the electrical. Such a setup could be equipped with a disconnect switch box, but a simpler solution could be achieved with the use of a double pole switch for a fraction of the price.

Double Pole Switch Applications

A double pole switch such as the one in Fig.1 is just slightly bigger than a regular switch but constructed as two single switches harnessed side by side and activated by one common toggle.

double pole breaker diagram

Double pole switches are usually rated at 30 amps, so any appliance or equipment requiring a greater power consumption have to be connected to a disconnect switch of the proper rating.

This piece is about installing a double pole switch for a hot water heater, a ceiling heater, a compressor, or anything else with less than 30 amps rating.

A 220 volt line can be wired up in two different ways, each for a specific purpose. If a double pole switch is to be added to a 220 volt line with a two-wire cable, only two wires will come through into the switch’s electrical box besides the copper ground wire. Each one of them is hot and carrying 220 volts (if tested across both wires). The second way is through a three-wire cable where one white neutral wire and two hot wires, one black and the other red, will be used.

Such a hookup is needed if some of the controls in the appliance or equipment run on 110 volts while the main part generating the action such as the motor or heater, needs 220 volts. If the white wire was to be measured across to the red or the black, 110 volts would be measured in each instance.

If a multimeter was put across the two colored (hot) wires however, the reading would be 220 volts, giving this type of wiring an extra option. Either way, the double pole switch is the one to be used, since, in each instance, it cuts both of the colored (hot) line OFF and stops the current flow. The following steps will illustrate how to do the installation.

double pole switch Figure 2

Part 1 - Install the Switch Box and Wires

This installation illustrated here uses a three-wire cable but it is exactly the same wiring at the switch in two-wire cable installation for the colored wires, except that the neutral (white) wires are to be ignored.

Step 1.1 - Shut off the Power

The first thing to do before starting the installation is to shut off the circuit breaker dedicated to the piece of equipment being worked on, in the main electric panel. Confirm that the power is OFF by trying to turn on the equipment.

Step 1.2 - Cut the Line

The 220V line going to the equipment will have to be severed in a spot near the equipment, but where there’s enough slack to wire up an electrical box. Before cutting the cable, place the electric box in a suitable location and fasten it in place.

If the cable is too tight to permit at least six inches from each end to extend into the box, cut the feed from the breaker first. To accommodate for the extra length, leave the cable to the appliance to either be spliced inside an added junction box or be replaced.

Step 1.3 - Prepare the Connection

Cut the cable, making sure that there are at least six inches of cable that are available to be fed through the box. Remove the appropriate knock-outs from the box and put the cable connectors in place.

Step 1.4 - Insert the Cable

Remove about six inches off the jacket from each end of the severed cable, and wrap black electrical tape on the piece of wire connected to the panel, at the junction were the jacket ends and the wires are exposed to indicate which line will be hot. Insert the cable through the connector into the electrical box, as shown in Figure 3.

double pole switch instructions

Step 1.5 - Strip the Wire Ends

Using a wire stripper or utility knife, remove 1/2 inch of the insulation from the end of the black, the red, and, if applicable, the white wire, as shown in figure 4.

The cable can then be put in its resting position and the cable connector tightened to keep it solidly in position.

double pole switch instructions

Step 1.6 - Connect the Cable to the Box

The cable length connected to the appliance, with a section of the jacket removed, is then installed into the electrical box and clamped in place with the cable connector as in Figure 5. The ends of the wires can then be also stripped of 1/2 inches of their insulation.

Step 2 - Hook Up the Switch

Step 2.1 - Connect the Neutral Line

At this point, if the cable has a neutral line, both neutral wires are to be connected together with a wire nut connector after which the ground wire from the 220V line is looped around and fastened to the ground screw terminal of the electrical box as shown in Figure 6. The end of this wire is then connected to the ground wire from the other cable leading to the equipment, and an additional piece about four inches long that will later connect on the switch (Fig. 6).

double pole switch installation

Step 2.2 - Add the Switch

The double pole switch can now be added into the circuit with both colored wires (the black and the red) coming from the circuit breaker connected to the black terminal screws on the switch as seen in figures 7 and 8. It doesn’t matter which color goes to which side of the switch since as mentioned before, it acts as two independent switches. The ground copper wire that was added in Step 2.1 can now be attached to the green ground terminal screw on the switch (Fig.8).

double pole switch installation

Step 2.2 - Connect the Cable

The appliance side of the cable can finally be connected to the switch’s terminals (Fig. 7 has a better view). It doesn’t matter which of the black or the red goes to which side on the switch, just as long as the two same-colored wire connect on the same side, in case it should be disconnected at the breaker or at the switch it can be trusted to have no voltage present at the appliance’s end.

Step 2.3 - Mount the Switch

With everything properly connected, the switch can be placed into its electrical box (Figure 9) and screwed in position and the cover plate added to give it its finishing touch.

double pole light switch

The breaker can now be turned back on and the switch put to the test.