How to add a circuit to an electrical panel

A home addition or remodel, upgraded appliances or new lighting can make it necessary to add an additional circuit or two to supply the additional power needed. Electricity can be very dangerous, even deadly. Follow this systematic approach to add a circuit to an electrical panel correctly and safely.

Open the panel door. Remove the screws that secure the cover to the panel box and set it out of your way.

Step 1

Open the electrical panel door. Remove the screws that secure the cover to the panel box and set it out of your way. Look for a circuit breaker that has no wires connected to it. If none is available, add a circuit breaker rated for the current you need for the new circuit. Starting at the new location, run the circuit back to the panel. Install the receptacles, switches and lights in the new location first, then return to the panel to connect the new circuit.

Turn off the main breaker in the panel. Remember: Even when the breaker is off, service cables coming into the panel are live and dangerous

Step 2

To add a circuit to an electric panel, turn off the main breaker in the panel. Remember: Even when the breaker is off, service cables coming into the panel are live and dangerous. Find the service cables – they may enter the panel from the top, side or bottom – and avoid contacting them. If you are working in a subsidiary breaker panel, shut off the power at the main panel or service breaker, so the subpanel has no live wires to it.

Step 3

Turn off the empty circuit breaker you are connecting to and use an insulated screwdriver to loosen the screw on the clip that secures the wire to the breaker. Locate an available knockout on the same side of the panel and remove it with pliers. Thread a cable guide/clamp through the knockout (with the clamp screws on the outside of the panel) and secure it with the locknut. Loosen the clamp screws on the guide/clamp.

Pull enough wire through the guide to allow you to run it to the bottom of the panel and back to the circuit breaker. Mark the outer jacket of the wire just inside the box, pull it out and cut the outer sheath at the mark.

Step 4

Pull enough wire through the guide to allow you to run it to the bottom of the panel and back to the circuit breaker. Mark the outer jacket of the wire just inside the box, pull it out and cut the outer sheath at the mark. Strip and remove the outer sheath. Remove the insulation from the wires.

Inspect the wire for nicks. If the wire is free of nicks, fish it back through the guide/clamp, being sure not to nick the wires, and tighten the cable clamp to secure it. Be sure the clamp tightens over a section of the wire that still has its jacket – not on the area of wire that is exposed.

If the wire is free of nicks, fish it back through the guide/clamp, being sure not to nick the wires, and tighten the cable clamp to secure it. Be sure the clamp tightens over a section of the wire that still has its jacket.

Take note: Most circuit breaker instructions specify the proper amount of torque to apply when tightening the screws on wire connections in the box. While it is unusual to measure torque when installing electrical equipment, there is a correct way to tighten the screws, and it’s quite firm. Under full current load, heating, thermal expansion and distortion of the copper wire can result, and if a screw is not tight enough, the wire can loosen which can lead to arcing and fire. If a screw is tightened too much, the threads can strip or the drive slot can burr over.

Locate the neutral bus (it is the bar with multiple white wires connected to it) and loosen one of the screws that does not have a wire on it. Insert the stripped section of the white wire into the hole and tighten the screw.

Step 5

Use wire strippers to remove about 3/4 inch of insulation from white and black wire ends. Locate the neutral bus (it is the bar with multiple white wires connected to it) and loosen one of the screws that does not have a wire on it. Insert the stripped section of the white wire into the hole and tighten the screw. Locate the grounding bus (it is the bar with bare copper or green insulated wires connected to it). Loosen one of the screws and connect the unsheathed ground wire to the grounding bus the same way.

Step 6

Slide the black wire into the circuit breaker clamp and tighten it. Tug the black wire to be sure it is tightly secured. Bend the wires into the panel so they are orderly.

If you’re adding a circuit breaker, install it into position. Slide the black wire into the circuit breaker clamp and tighten it. Tug the black wire to be sure it is tightly secured. Bend the wires into the panel so they are orderly. Double-check the connections you made before replacing the panel cover.

Step 7

Turn every breaker in the panel off and then turn the main breaker on. Toggle all the circuit breakers on one at a time. With all breakers on, go to the new circuit and test outlets or fixtures for power and correct polarity. Add the location of the new circuit to the list inside the electrical panel’s door.

—By Steve Sturgess

DISCLAIMER: Home improvements, repairs, remodeling and construction are inherently risky, even dangerous. If you attempt this type of work, you do so at your own risk. Check state and local codes before starting any project. Follow all safety precautions. Every effort has been made to ensure accuracy and safety in this feature; however, Pro Construction Guide’s publishers, contributors and advertisers can not be held responsible for damages or injuries resulting from the use of the information in this document.