How to Install a GFCI Outlet in a Garage

Garages are inherently damp, fluctuating environments that pose a significant risk for electrical shocks when using power tools or appliances. A Ground Fault Circuit Interrupter, or GFCI, is the only device capable of monitoring current flow and cutting power instantly if it detects a leak, potentially saving a life in the event of a ground fault. Installing a GFCI is a straightforward process if you respect the power and follow proper wiring protocols. When done well, the outlet will test correctly, provide reliable power, and sit flush against the box for a professional finish. Treat every wire as if it is live until you have proven otherwise with your tester.

Kill the Power First. Head to your breaker panel and switch off the circuit that feeds your garage outlets. Plug a lamp or a voltage tester into the outlet you intend to swap to confirm the power is truly dead before proceeding.
Extract the Old Outlet. Unscrew the wall plate and the mounting screws securing the receptacle to the electrical box. Gently pull the outlet out of the box, exposing the attached wires.
Spot Line from Load. Use a non-contact voltage tester to confirm no wires are live. Disconnect the wires and separate them; if you have two sets of black and white wires, you must determine which pair is the 'line' (incoming power) and which is the 'load' (outgoing power to other outlets).
Wire the GFCI Correctly. Attach the incoming line wires to the terminals marked 'LINE' on the back of the GFCI. Connect the bare or green copper wire to the green grounding screw.
Mount It Flush and Neat. Carefully fold the wires back into the electrical box, ensuring no strands are touching the metal sides of the box. Screw the GFCI into the mounting bracket until it is snug and level.
Verify It Works Right. Restore power at the breaker panel and press the 'Reset' button on the GFCI. Use your plug-in circuit tester to confirm the outlet is wired correctly and that the 'Test' button successfully trips the power.