Wiring Instructions for a Main Breaker Box

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An old breaker box or fuse box can be a fire hazard. Depending on how old the box is replacement breakers may be unavailable or prohibitively expensive. Either way, the best solution is often a new main breaker box. It can be quite expensive to hire an electrician to do the job so if there are no local laws prohibiting it, you may want to wire your own new breaker box.

Call your electrical utility and have the company send a technician to disconnect the electrical service.

Use the pliers to punch out enough of the pre-cut holes in the box to accommodate all of the circuits. Install a cable clamp, usually included with the new breaker box, in each hole. Insert all wires through the clamps. Pull the slack out of the wires and tighten the clamps.

Separate the individual wires in each circuit. Strip 1/2-inch of insulation from each wire end. Connect all of the ground wires to the ground bus, the metal bar with holes and screws in it. Tighten the screws to retain the wires.

Connect all of the neutral wires to the ground bus. The neutral wires are usually coated with white insulation. Tighten the screws to retain the wires. Do not connect any neutral wires in the same hole as a ground wire, though they are connected to the same bus.

Follow the panel directions to insert the double-pole breakers. These are the breakers with two screw connections. Start from the top of the panel and install a breaker on the left and right sides, and work your way down until you have a breaker for each 240-volt circuit. Use 20-amp breakers for 12-gauge wires, 30-amp breakers for 10-gauge wires, 40-amp breakers for 8-gauge copper or 6-gauge aluminum wires, and 50-amp breakers for 6-gauge copper or 4-gauge aluminum wires.

Connect the black wire of each 240-volt circuit to its corresponding breaker. Connect the red wire of each circuit to the second terminal of its corresponding breaker. Tighten the screw terminals.

Install a single-pole breaker for each 120-volt circuit. Continue working downwards and installing breakers on both the right and left sides of the box. Use 20-amp breakers for 12-gauge wires, and 15-amp breakers for 14-gauge wires. If there are any 10-gauge, 120-volt circuits use a 30-amp breaker for each of those.

Connect the black wires from each circuit to its corresponding breaker. Tighten the terminal screws.

Visually double check the outside meter to verify that it is off. If the meter is present but powered off, it will be sideways from its normal, readable position. If in doubt, use the multimeter to verify that there is no voltage present across the feed wires inside the house. Connect one of the large black feed wires to one of the terminals of the main breaker in the top of the box. Connect the other black wire to the other terminal of the main breaker. Connect the large neutral wire and the solid copper ground wire to the ground bus.

Call the utility company to reconnect the electrical service.


  • Never work on the main feed wires if the meter is installed in the "on" position. If you need to work on the individual circuits in the breaker box while the meter is installed, first turn off the main breaker.
  • If you are unsure of your ability to perform this work, hire a licensed electrician.
  • Check your local laws before performing your own electrical work.
  • If possible, have a second, knowledgeable person double check your work before you turn the electricity back on.


  • "The Complete Guide to Home Wiring"; Andrew Karre; 2005

About the Author

Since 2008 Tracy Underwood has been fulfilling a lifelong dream of writing professionally. He has written articles for Possumliving.com and Woodsloafing.com online, and in print for "Backwoodsman Magazine." Underwood holds an Amateur Extra license from the FCC. He received an Electronic Technician certificate from the U.S. Navy BE/E school, NTC Great Lakes.

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