Build a Garage Electrical Circuit

Garages demand real electrical capacity. Power tools pull serious amperage. Compressors cycle hard. Work lights stay on for hours. A single 15-amp bedroom circuit shared with the kitchen won't cut it when you're running a table saw and a shop vac simultaneously. Most garages get by with a single 20-amp circuit feeding outlets and overhead lights, though serious workshops benefit from two circuits or a 240-volt line for heavy equipment. The work itself is straightforward: pull cable, make connections, test everything twice. The thinking happens before you strip the first wire—planning the layout so outlets land where you'll actually use them, sizing the circuit for both current load and future expansion, and routing cable in a way that won't interfere with garage door hardware or wall-mounted storage. Done right, this circuit becomes invisible infrastructure that just works, year after year, no matter what you plug into it.

1. Plan Every Outlet First. Walk the garage with a notepad and mark where you need outlets and switches. Count everything you might run simultaneously—tools, lights, chargers, refrigerator if you keep one out there. Add up their amperage. If the total exceeds 16 amps sustained, you need a 20-amp circuit. Mark outlet heights at 18 inches above the floor, switched light locations, and the path your cable will run from the main panel.
2. Secure Your Breaker Slot. Kill the main breaker. Remove the panel cover. Knock out a slot on the panel's side or bottom where your new cable will enter. Install a 20-amp single-pole breaker in an open slot—it snaps onto the bus bar with firm pressure. Leave it in the off position. Do not connect any wires yet.
3. Thread Cable Through Walls. Drill through the wall plate behind the panel if needed, then run 12/2 NM cable through the walls to your first outlet box location. If walls are finished, you'll run along the ceiling or in surface-mount conduit. Staple cable every 4 feet and within 12 inches of each box. Leave 8 inches of cable hanging at each box and 12 inches at the panel. Use cable clamps at every box entry point.
4. Mount All Outlet Boxes. Mount old-work boxes at marked outlet locations if walls are finished, or nail-on boxes to studs if walls are open. Position outlet boxes 18 inches above floor level. Switch boxes go 48 inches up. Secure each box firmly—loose boxes create loose outlets that fail over time. Feed your cable into each box through the built-in clamps and tighten the clamp screws.
5. Connect Every Terminal Tight. Strip half-inch of insulation from each wire. At outlets, connect black wire to brass screws, white to silver screws, ground to green screw. Pigtail connections if you're running to another outlet downstream—don't rely on the outlet itself as a splice point. At switches, black wire to brass terminals, white wire gets taped with black electrical tape to mark it hot, ground to green screw. Fold wires into boxes neatly and screw devices to the box ears.
6. Hook Breaker to Hot Wire. At the main panel, strip the cable sheath back 10 inches inside the panel. Connect the bare ground wire to the ground bar. Connect white neutral to the neutral bar. Strip half-inch from the black hot wire and connect it to the brass terminal on your new breaker. Tuck all wires neatly along the panel edges. Install the panel cover.
7. Verify Power Everywhere. Turn the main breaker back on, then flip your new breaker on. Use a multimeter to verify 120 volts at each outlet. Plug in a lamp and test every outlet. Flip each switch to verify it controls the intended light. Use a three-prong outlet tester to verify correct polarity and ground at every receptacle. If anything reads wrong, kill the breaker and recheck your connections.
8. Document Your Work. Write a clear label on the breaker in the main panel—GARAGE OUTLETS or GARAGE CIRCUIT 1. Take photos of the panel, the circuit routing, and all box locations. Put a small circuit map on paper and tape it inside the panel cover. Mark the amperage and wire gauge right on the label so you or anyone else knows what the circuit can handle.