How to Build a Parallel Circuit

Building a parallel circuit is necessary in home wiring to create a fail safe pathway for an electrical current. A 15 amp breaker on a main circuit panel can safely power several outlets and lights in the loop. Wiring the circuit in parallel ensures that if one outlet or light fails, the whole circuit will continue to function. This how-to will, for simplicity’s sake, describe the wiring of a parallel circuit with only two outlets: one in the middle, one at the end. The principle, however, is the same even for more complicated circuits. 

Step 1: Turn Power Off at Main Panel

At the main circuit panel, turn the power off to the circuit on which you working. This requires flipping the switch on the circuit to ensure no current flows through it. 

Step 2: Run Romex From Panel to First Outlet Box

In a pre-existing home, this may be more involved, but after connecting the Romex cable to the individual circuit, run the cable to the first outlet box in the room where it will be installed. There should be plenty of slack, enough so that 6 inches of the cable can be fed in through the bottom of the outlet box. 

Step 3: Strip the Romex, Separate the Wires

Strip away about 6 inches of the outer insulation on the Romex and separate the three wires inside. On the black and white wires, strip away about an inch of insulation. If the third wire is green, strip an inch off that as well. 

Step 4: Connect First Outlet

On the outlet there are five screws: two brass, two silver and one green. Connect the black wire to the lower brass screw and the white wire to the lower silver screw. With a spare 6-inch length of green or bare wire, connect it to the green screw.

Step 5: Run Cable Out of the Box to Second Box

Next, run another length of Romex cable through the top of the first box to the second box. Again, leave 6 inches of cable in both boxes. 

Step 6: Finish First Outlet Connection

Strip the insulation from the Romex feeding through the top of the first box as in step 3. Strip the individual wires in the same way as well. Connect the free black wire to the upper brass screw and the other white wire to the upper silver screw. Take a wire nut and pigtail the two bare or green wires from both cables and the third length attached to the outlet. 

Step 7: Connect Second Box

In the second and last outlet box, strip the Romex and the individual wires in the same manner as step 3. Connect the black wire to the upper brass screw and the white wire to the upper silver screw. Pigtail the protruding bare or green wire with a second short length of the same. Connect this short length to the green screw on the second outlet. 

Although it only involves two receptacles, you have nonetheless built a parallel circuit. While power flows to the first outlet from the source, it simultaneously bypasses it and supplies power to the second outlet. Should the first outlet fail, the second outlet will continue to function. Turn the circuit breaker back on and test your work.