How to Put in a Sub-Panel Breaker Box
- 1). Mount the empty subpanel breaker box onto the wall. Use masonry or wood screws to attach the subpanel to your structure.
- 2). Run the four-conductor NM cable from the main panel to the subpanel. Size your NM cable according to the size of the double-pole breaker you will use to feed the power to the subpanel.
- 3). Attach the four-conductor NM cable to the subpanel breaker box. Remove the knockout from the subpanel and install a cable clamp. Remove the knockout by placing a screwdriver onto the knockout and hitting the screwdriver with a hammer. The cable clamp will slip into the knockout hole and a lock nut holds it into place. Feed the cable through the cable clamp and tighten the screws of the clamp to hold the cable into place.
- 4). Connect the wires onto the subpanel breaker box. Use a dual NM wire cutter/stripper to remove the sheath from the four-conductor NM cable exposing the black, red, white and bare copper wires. Strip 1/2-inch of insulation from the wires. Attach the red and black wires into the main lugs located on the center or hot bar using a screwdriver to tighten the lugs and hold the wires in place. Attach the white wire to the neutral bar located to the right or left of the center bar and connect the bare copper wire to the ground bar located at the bottom of the panel. Tighten the lugs to hold the wires in place. The neutral and ground bar resemble the silver bars with screws located down the entire length of the bar. Place the cover on the subpanel until you run your circuits.
- 5). Install your double-pole feeder breaker into your main electrical panel. Turn off the main breaker and remove the panel cover, exposing the wiring inside the panel. Test to verify the power is disconnected by placing one prong of an electrical tester onto a screw at the back of any breaker and the other prong to any metal on the panel. If the tester does not light, then you have disconnected the power correctly. Slip the back of the feeder breaker into the slot located in the breaker panel and push it firmly over the center buss bar. The slot, located at the back of all other breakers, allows the rear lip of the breaker to slip under the slot and holds it into the base.
- 6). Strip the NM cable at the main panel. Remove the sheath from the cable exposing the black, red, white and bare copper wires. Strip a 1/2-inch of insulation from the ends of the wires. Connect the black and red wires into the back of the feeder breaker, slipping them under the set screws and tightening the screws to hold the wires into the breaker. Connect the white wire to the neutral bar and tighten the set screw to hold the wire in place. Connect the bare copper ground wire to the grounding bar. Replace the panel cover and turn off the feeder breaker until you run the sub-panel circuits. Turn on the main breaker.
