How to Wire Double Breaker Boxes

Open the service panel and remove the cover over the circuit breakers. Touch one probe of your volt meter to the bar to which the white wires are attached -- this is the neutral bus bar -- and touch the other probe to the metal of the circuit bus bar. If there is any voltage reading, do not work on the breaker box. If you can't figure out how to switch off the power, call an electrician.

Punch out the knockout hole in the side of the breaker box so you can feed in the wire for the new double breaker circuit. Put a screwdriver tip on the hold and tap on the handle with the hammer until the knockout comes loose. Feed the 3-wire with ground cable through the hole.

Strip off 12 inches of the outer sheath of the cable to expose the inner wires. Strip the last half an inch of insulation from the constituent wires.

Insert the bare metal of the green or bare wire into the ground bus terminal and tighten the screw. Insert the exposed metal from the white wire into the neutral bus terminal and tighten the screw. Some older panels have only one, joint bus for both the ground and the neutral wires. If this is the case, connect bot the ground and the white wire to that bar.

Insert the red wire into one of the terminals on the double-pole circuit break you want to install. Tighten the screw to hold it in place. Insert the black wire into the other terminal and tighten the screw. It doesn't matter which wire goes into which terminal, because they will both carry the same electrical load.

Push the double breaker into the breaker bus bar below the last breaker in the panel. If it's a clip model, simply press it firmly into place. If there are screws, tighten them firmly. Repeat this process for all the double breaker switches you want to install in the breaker box.

Knock out the space in the cover panel for your new double breaker, then reinstall the cover.