Most older homes were built with few, if any,
outdoor receptacles. But it's not that difficult to add one. If you don't
already have the tools for this electrical work, don't worry: they're
inexpensive and easy to find. You'll use most of the same parts you'd use for
installing an indoor receptacle; the main difference is that you need a
wiring box and cover rated for outdoor use. Here's how to get the job done.
To add a single receptacle that's mounted on an exterior wall, it's
usually best to tap into a nearby interior receptacle, such as one in a
bedroom or living room. Do not tie into circuits for heavy-duty units like
dishwashers, dryers and heaters; those circuits are already dedicated to
these high-draw appliances. To get the power you need for an outdoor
receptacle without risking overload, it's best to feed from a 20-amp circuit
rather than a 15-amp one.
One more detail worth noting: there are two kinds of exterior box covers.
One has a spring-type lid that areweathertight only when shut. The other cover's lid is
rated to be watertight while in use. If you intend to keep something plugged
into your outdoor receptacle Christmas lights, for example the cover must be
labeled "watertight while in use." It's against code to keep
something plugged into the spring-lid type.
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Step by Step 1. Tap into a receptacle. Turn off the power to the receptacle, and
check it with a plug-in tester to verify that the power is off. Remove the
cover plate and unscrew the two screws that hold the receptacle to the outlet
box. Pull the receptacle out of the box as far as it will go, and disconnect
it by removing all the wires from its terminals.
If the box is metal, remove the mounting screws from the wall and gently
pull the old outlet box a few inches out of the wall and push it to the side.
If the existing wires are too short to let you do that, detach them from the
box. Then use a slotted screwdriver with a broad blade to break off or pry
open a knockout anywhere in the box. This is where your new cable will come
in to feed the outdoor receptacle.
If the box is plastic, you may need to use a hacksaw to
cut the mounting nails that extend into the adjacent stud. Removing the box
could be so messy that you should find another source of power, like tapping
into a cable in the basement.
2. Run cable to the new box. With the old outlet box pulled off to
the side, you should now be able to see into the wall cavity. Pull apart the
insulation and make sure that there's nothing inside the wall such as
plumbing that you could damage by drilling into the wall from the outside.
For ease of installation, the new outside outlet box should be in the same
wall cavity as the box you're tapping into, or just below that cavity, in a
joist space that's accessible from the basement or crawl space. Walk outside
and try to find the exact spot where the wall cavity is. If you're not sure,
drill a tiny (1/8-inch-diameter) hole from inside to outside to provide a
reference point. (Seal it later with clear silicone caulk.) You can use the
same strategy to locate the joist space below the box, this time drilling
through the floor. Use a 1/2-inch spade bit to drill up into the wall cavity
from below, as shown.
Pick a spot on the exterior wall that will allow the back of the new
outlet box to fit flat against it. It doesn't matter if the wall siding is
angled as long you can mount the box flat. At this spot, drill a
1 1/4-inch-diameter hole that's 5/8 inch deep; this hole provides
clearance space for the cable clamp on the backside of the box, so it can lie
flush to the siding. Then, using a 1/2-inch spade bit, finish drilling
through the exterior wall and into the wall cavity or joist space. (You
could, of course, drill all the way through the wall with a 1 1/4-inch
spade bit, but a 1/2-inch hole is easier to caulk and big enough to
accommodate the cable.)
Push the length of new cable through the hole and into the wall cavity or
joist space. Then fish the cable up through the old receptacle cutout. For
now, leave 8 to 10 inches of slack cable sticking out beyond the siding and
interior wallboard.
3. Mount the new watertight box outside. Bring the new cable
through a hole in the back of the outdoor outlet box, securing it to the back
of the box with a cable clamp. Fill the hole with silicone caulk and screw
the box into place (the clamp will fit into the 1 1/4-inch-wide hole),
then caulk all around the joint between the outlet box and the siding. For a
joist space installation, use the same caulk to fill the voids around the
cable where it penetrates the joist.
4. Hook up the outside wires. Now you're ready to hook up your
wiring. Cut away any cable that extends more than 4 inches beyond the front
of the box. Strip all but 1/2 inch of the sheathing off the cable; that 1/2
inch section is the portion resting beneath the clamp. Then strip 1/2 inch of
insulation off the individual wire ends. Find the two LINE terminals on the
GFCI receptacle. Ignore the LOAD terminals, because you will not be
extending the circuit beyond this receptacle. Attach the black wire to the
LINE gold screw and the white wire to the LINE silver screw. If the outdoor
box is metal, you'll need to ground it: Loop the bare copper grounding wire
under the box's ground screw before you attach it to the receptacle, and
tighten the box's ground screw. Then attach the grounding wire to the
receptacle's green screw. Once done, stuff the receptacle into the box, fit
the gasket over it and install the weatherproof cover. You're done outside.
5. Rewire the interior receptacle. Back at the
interior outlet box, use a cable clamp to connect the new cable to the box
(some old metal boxes won't need a clamp) and remount the box in the wall.
You'll likely have two or three cables now. If there are only two (one
original cable feeding the box, plus your new cable), you can strip and
secure the black and white wires from the new cable to the receptacle (black
to brass, white to silver).
If there are three cables (two existing cables and the new one) and the
receptacle's terminals are filled, use a wire connector to splice all the
black wires together along with a short "jumper" wire that can be
attached to one of the brass-colored "hot" screws on the
receptacle. (The jumper wire provides a bridge between the spliced wires and
the receptacle.) Splice the white wires and the ground wires in the same
manner and attach both of these jumper wires to their respective screws, as
shown. Once all splices and connections have been made, gently fold the wires
back into the outlet box, screw the receptacle back into its place and
reinstall its cover plate.
6. Test your work. Turn the power back on, and check both
receptacles for proper wiring with a plug-in tester. At your new outside
receptacle, press the GFCI's TEST button. It should
trip off with an audible click, and the lights on the plug-in tester should
go out. Press RESET. You're done.
