Wiring a GFCI
1 of 4
Photo 1: Remove the outlet
Turn off the
power at the
main circuit panel
and remove the old outlet.
wires by clipping them
close to the outlet.
2 of 4
Photo 2: Strip the wires
from the wires
to expose the
amount of wire
shown on the
located on the
back of the
the hot and
power to the
of the GFCI. The
terminal for the
neutral wire will
3 of 4
Photo 3: Connect other outlets
Remove the tape covering the “load” terminals and connect the
wires leading to another outlet or outlets to these terminals. Again,
the white neutral terminal will be marked. Fold the wires back into
the box and screw on the GFCI and cover plate.
4 of 4
Photo 4: Label the outlets
Attach the “GFCI-protected outlet” label to downstream outlets.
Test the downstream outlet by plugging in the GFCI tester and
pressing the test button. The lights on the tester should go out.
Press the reset button on the GFCI to reenergize the outlet.
GFCI outlets reduce the
danger of deadly shock
from faulty plug-in
devices. A GFCI
(ground fault circuit
interrupter) is a special
type of outlet that detects dangerous
ground faults and immediately
turns off the power to stop
shocks. You can
replace almost any electrical outlet
with a GFCI outlet. Correctly
wired GFCIs will also protect other
outlets on the same circuit.
While it's common to find GFCI
outlets in bathrooms and kitchens,
the electrical code also requires
GFCIs in unfinished basements,
garages, most outdoor receptacles
and places where construction
activity occurs. We'll show you how
to replace a standard duplex receptacle
with a GFCI and wire it to protect other outlets. (For more information about wiring outlets, see Wiring Switches and Outlets).
You'll need a screwdriver, a
wire cutting and stripping
tool, and an inexpensive
voltage tester. We also recommend
you add a
GFCI tester to your
tool drawer. GFCI testers are available at home centers and
hardware stores and
are a handy device for troubleshooting
standard outlets as
well as GFCIs.
Before you start, locate the circuit
breaker or fuse that controls
the outlet you plan to replace and
shut off the power to the circuit.
Plug a lamp, radio or the GFCI
tester into the outlet to test for
power and make sure it's off. Then
unscrew and pull out the old outlet
and count the number of wires
in the box. Calculate the minimum
box size required for all of
the wires plus the GFCI (see
“Required Box Size,” below). If the
existing box is large enough, follow
the steps in Photos 1 – 4 to
replace the outlet with a GFCI. Replace an undersized box with a
new one of adequate size. (For more information on box replacement, see What You Should Do With Crowded Electrical Boxes).
Using a GFCI to protect additional
outlets on the same circuit
breaker or fuse can be tricky.
Don't do it unless you know
exactly where the wires go. In the
workshop, we had the advantage
of being able to visually trace the
Test all the GFCIs in your house
at least monthly by pressing the
test button or using your GFCI
tester. If an outlet fails to trip,
replace it with a new one.
Required Box Size
To figure the minimum box size
required by the National
Electrical Code, add:
1 – for each hot and neutral wire
entering the box
1 – for all of the ground wires
1 – for all of the cable clamps
combined (if any)
2 – for each device (switch or
outlet—but not light fixtures)
Multiply the total by 2 for
14-gauge wire and 2.25 for
12-gauge wire to get the
minimum box size required in
cubic inches. Plastic boxes have
their volume stamped inside.
Steel box capacities are listed
in the electrical code.