Test a GFCI Outlet with a Multimeter: Safe Step-by-Step Guide

Wondering if your GFCI outlet is actually protecting you?
A quick multimeter test tells you in minutes whether the device is passing power and tripping correctly.
Follow this safe, step‑by‑step guide to test a GFCI outlet with a multimeter and reset it confidently.

Preparing Your Multimeter

Always keep your hands dry and use insulated probes. Never touch live wires with bare fingers.
You’ll need a digital multimeter set to AC voltage (V~). Plug the black probe into the COM jack and the red probe into the VΩ jack.

How to Test a GFCI Outlet with a Multimeter

With the faceplate on, insert the red probe into the shorter slot (hot) and the black probe into the longer slot (neutral) — the line and neutral connections. You should see a steady voltage reading around 110‑120 V in the US. If the number fluctuates or reads zero, the GFCI may not be passing power correctly.

Keep the red probe in the hot slot and move the black probe to the D‑shaped ground hole. You should still see roughly the same voltage. A low or missing reading here indicates a compromised ground path.

Press the test button on the outlet while watching the meter. The voltage should drop to near zero when the GFCI trips. Release the test button and hit reset; the voltage should jump back to normal. If it doesn’t, the device isn’t resetting properly — a sign the trip mechanism is faulty.

Press the reset button firmly until it clicks. Plug in a lamp or phone charger to confirm the outlet stays on. If it trips again immediately, you’ve confirmed a fault and should replace the unit or call a professional.