How To Run A Junction Box Line From Your Breaker Box

Posted on: 29 September 2016


If you're planning on adding an additional electric line to handle the ever increasing need for power outlets, you should consider adding a junction box at some point along the line instead of running the line directly to a single outlet.

Although you can run additional lines from an outlet, you are more limited in the direction that the additional lines may follow. When branching from an individual outlet, it's much easier to run a line in the same general area as the outlet.

When you are adding a line from a more centrally located junction box, you can branch out in various directions and avoid more obstructions in walls and ceilings as you attempt to run wiring.

What is a junction box?

A junction box is essentially an empty metal or plastic box that is used to conceal and protect wire connections. Some junction boxes are completely empty and are made for wires that are simply twisted and taped together.

Other more deluxe junction boxes have terminals inside to which you can make multiple wiring connections. All junction boxes have scored punch-out holes in the sides for wires to enter and exit, and a removable cover that allows connections to be made once the box is installed.

What you will need to install a line with a junction box

Junction box

Electric wire: It is advisable to install a 20 amp line rather than a 15 amp line. Both are used in residential electric services, but a 20 amp line will allow more branch lines to be added later. That being said, you will need at least a three wire sheath of 12 gauge wire for a 20 amp line. Don't try to save money by buying less expensive lighter gauge wire, because you risk overheating the wire and causing a fire hazard. Measure the distance from your breaker box to the proposed location of the junction box, then add several feet to the result to allow for connection purposes and obstructions when running wire.

1/2" flexible conduit with connectors: This is flexible pipe that will protect the new wiring from damage. You will run wire through the conduit between the two connection points. Use you wire length to determine the length of conduit needed.

20 amp circuit breaker: You must buy a breaker from the same manufacturer as your breaker box, or a compatible aftermarket substitute, or the breaker may not fit inside your box.

Wire stripper tool


Installing the junction box

Knock out one of the punch -out holes in the sides of the junction box, then twist a conduit end connector into the hole and attach one end of the conduit to the connector. Place the box against the wall or ceiling at the planned location and screw it into the wall or ceiling.

Stretch out the roll of conduit along the path that you intend to use to reach the breaker box. When you have reach the box, cut the conduit to the length required. You will then begin to feed the sheath of wire into the box and through the conduit until you reach the breaker box location.

Installing and connecting the breaker

Working inside the breaker box requires turning off the main breakers to the home. These may be located on top of the other breakers on in a separate location.

When this is done, you will remove the cover panel of the breaker box with a screwdriver. Knock out a punch-out hole in the side of the breaker box nearest to an available breaker slot, and connect the end of the conduit to the box with an end connector.

Use your screwdriver to punch out the scored covering on the available slot.

Use the stripper tool to strip 3/4 inch of insulation from the ends of each of the three wires in the sheath. You will then connect the white and copper (or green) wires to the white grounding bars inside the breaker box. Slip each wire into the hole behind a terminal screw and tighten the screw.

The black wire will be connected to the single terminal screw on the circuit breaker. You will then push the breaker into the slot until it clicks into place.

Reattach the cover plate to the breaker box, then turn on the main breakers. Leave the new breaker to your new junction box off and wrap the end of the wire sheath inside the box with electrical tape until you're ready to start making connections. 

Contact a company like Alpine Electrical Construction LLC for more information.