Overview: Project scope, special tools, materials and costs
Dragging extension cords across the yard to
power the weed whip, fumbling around in
a dark shed...most of us take these hassles
for granted. But it doesn't have to be that way. With a day's
work, you can run electrical lines to any part of your yard.
This article will show you how to bring power to a shed,
but the process is almost identical if you want to simply
mount an outlet on a post planted in the soil. A licensed
electrician would charge at least several hundred dollars
plus materials to run lines from your house to a shed 50 ft.
away (not including any work inside your house). You can
do the job yourself for a materials cost of about $140.
We'll show you how to run wires through rigid metal
conduit (RMC). This method offers the best protection of
the wiring and requires the least amount of digging. It also
lets you install a GFCI outlet at the end of the line rather
than at the house, which means you'll never have to run
back to the house to reset a tripped GFCI. For information
on completing the wiring inside the outbuilding or connecting
to power in your house,
type “wiring” in the search box above.
If you want to provide a dedicated circuit to the shed, hire
an electrician to make the final connection in your main
electrical panel. Otherwise you can connect to an existing
circuit if the circuit has enough capacity and the box you're
connecting to has enough volume for the additional wires.
To run the wires inside rigid conduit, you'll need a hacksaw,
a pipe bender capable of bending 1/2-in. rigid conduit
with an outside diameter of 3/4 in. (about $30), and a fish tape
long enough to reach through the buried pipe ($15 to $60).
You'll also need a pair of pipe wrenches to screw the sections
of pipe together, a drill and 1-in. bit capable of penetrating
your siding, and wire cutting and stripping tools.
The total cost of this project is typically about $2.20 for
every foot of buried conduit, plus about $25 for LB fittings
and miscellaneous hardware.
A few weeks before you start the project, contact your
local building department to obtain an electrical permit if
one is required. Then a few days before you dig, call 811 to
have your underground utility lines marked. Learn more at
call811.com.
Metal Conduit Means Less Digging
Running wires inside rigid metal conduit
(RMC) is a little more expensive than
burying underground feeder cable (UF),
but it saves labor. That's because the
top edge of RMC has to be only 6 in.
below the surface of the ground, while
UF must be buried 12 in. deep (deeper
in some situations). That extra 6 in. of
trench depth may not seem like a big
deal, but it adds hours of backbreaking
work, especially if you have rocky soil,
hard clay or lots of tree roots.
Step 1: Plan the conduit route and dig the trench
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Photo 1: Dig the trench
Use a mattock to dig the trench. The narrow head means less
dirt to remove and less to put back. Slice out strips of sod with a
spade so you can neatly patch the lawn later.
There are several factors to consider in planning the route
from the house to the shed. Obviously the shorter the trench,
the less digging you'll have to do, but you also have to determine
where you're going to connect to power inside the
house and how easy it will be to get there. In some cases, a
little more digging could save you from having to tear into a
basement ceiling. Start by locating a power source, whether
it's your main panel, a ceiling box, outlet or other electrical
box. Then figure out the best spot for the new conduit to
enter the house. Since the National Electrical Code (NEC)
limits the number of bends you can make in the pipe to a
total of 360 degrees, you have to plan the route carefully.
The two 90-degree bends from the ground into the house
and shed consume 180 degrees, leaving you 180 degrees
more for any additional bends.
With the route planned, you can measure for the amount
of wire and conduit you need and head to the hardware
store or home center. Add 10 ft. to the length of wire and
pipe to make sure you'll have enough.
It's smart to drill the hole into the house before you start
digging just in case you run into an obstacle and have to
choose a new location. When you're sure of the exit point,
dig a trench from the house to the shed. If you're going
across a lawn, remove a slice of sod the width of a spade
from the surface and set it aside to reuse after you bury the
pipe. Then use a mattock or narrow spade to dig the trench
(Photo 1). Pile the dirt on plastic tarps so you don't have to
rake it out of the grass later.
Step 2: Mount the LBs and metal boxes
The rigid conduit will come out of the ground and into a
fitting called an “LB.” The LB has a removable cover that
simplifies the task of pulling wire by eliminating a sharp
right-angle turn. The trickiest part of this project is mounting
the LBs and connecting them to metal boxes inside the
house and shed. In general, you'll have to choose a box
location and then calculate the length of electrical metallic
tubing (EMT) needed to reach from the back of the LB to
the box. If you're going into a basement or crawl space, the
length of the conduit usually isn't critical. Start by drilling
a small hole with a long bit to make sure you're in the right
spot. Then drill a 1-in. hole for the LB and conduit. Screw a
1/2-in. conduit connector into the back of the LB and then
attach a piece of 1/2-in. EMT that's long enough to reach an
easily accessible box in the basement or crawl space. After
you've mounted the LB to the siding, go inside and add a
conduit connector and a metal electrical box to the other
end of the EMT. This box is where you'll make the connections
from your house wiring to the new shed wiring.
On the inside of the shed, you'll screw a 4 x 4-in. square
metal box to the side of the stud. Then connect the LB to
the box using the parts shown in Figure B.
Figure B: Through-the-wall parts
Figure B: Through-the-Wall Parts
Running the conduit through the wall to an inside box is the most difficult step.
Step 3: Run the metal conduit
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Photo 2: Plan the bend
Measure from the bottom of the trench to the bottom of the LB
fitting. Mark that measurement on the conduit.
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Photo 3: Bend the conduit
Pull back on the conduit bender until the end stands straight up. A
magnetic level lets you know when you've got a perfect 90-degree
bend.
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Photo 4: Join the conduit
Assemble the conduit run aboveground to make tightening the
connections easier. Support the conduit with 2x4s until youve
connected all but the last section.
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Photo 5: Plan the last piece
Measure for the last section of conduit. Adjust the measurement
for the distance the LB protrudes from the wall. Then mark the pipe
and bend it.
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Photo 6: Mark and cut
Hold the bent conduit in place to mark it for cutting. Since there
are no threads on the end of the pipe, screw a compression fitting
into the LB and connect the conduit to it.
The 10-ft. lengths of RMC are threaded on both ends and
include a coupling on one end. You'll start by bending the
first pipe and threading an LB onto the end. Then thread
the pipes together one at a time until you reach the other
end, where you'll cut and bend the last piece of conduit to
fit and connect it to the LB with a compression connector.
Photos 1 – 6 show the process.
Temporarily attach the LB to the shed and measure
between it and the bottom of the trench (Photo 2). Add 3/4 in.
for the threads that'll go into the LB and subtract the bending
allowance listed on your bender (usually 6 in.) from this
measurement for the bend. Mark this length on a piece of
conduit, measuring from the end with bare threads. Then
find a level spot to bend the conduit. Align the mark on the
conduit with the arrow on the bender. Push with your foot
and pull back on the pipe handle to bend the pipe (Photo
3). Use a level or the bubble built into some benders to tell
when you reach 90 degrees. Take the bent conduit back to
the trench and screw the LB onto the end. Photo 4 shows how
to connect lengths of conduit until you reach the house.
Bend the last piece of conduit up and cut it off to fit into
the compression connector (Photos 5 and 6). Start by measuring
from the last piece of conduit to the house wall (Photo
5). If the LB is held away from the wall by siding, subtract
this distance from the measurement. Then add 3/4 in. for
the threading and subtract for the bend. Mark the last piece
of conduit, starting from the bare threads. Once again, place
the bender arrow on the mark and bend the conduit. Face
the threaded end of the conduit when you make this bend,
not the end with the coupling. Mark the conduit (Photo 6)
and cut it with a hacksaw. Remove burrs from the inside of
the pipe by smoothing with a file or by inserting the bare
metal handles of pliers into the pipe and twisting. Complete
the conduit run by threading on the last piece of conduit.
You'll have to lift the previous piece of conduit to create
clearance as you spin the bent pipe around. Finally, slip
the end of the conduit into the compression connector and
tighten the compression nut with a wrench. Wrap a conduit
strap around the conduit and screw it to the house to secure
the conduit. Also press a rope of “duct seal” around the top
of the LB to keep water out.
Step 4: Pull and connect the wires
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Photo 7: Tie the wire to the fish tape
Feed the fish tape through the conduit. Loop the wires through the
fish tape and wrap them with electrical tape. Also wrap the hook
on the fish tape so it can't snag. Use stranded wire, not solid wire.
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Photo 8: Pull the wires
Pull the wires through the conduit. This is a two-person job—you
need a helper at the other end to feed the wires into the conduit.
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Photo 9: Start with a switch
Connect the wires inside the shed to a switch. Then run them to a
GFCI receptacle.
Remove the covers from the LBs and push a fish tape
through the conduit. Then pull the wire through the conduit
(Photos 7 and 8). You'll need two wires, one white and
one black, for one circuit, or more if you intend to wire a
three-way switch from the house or add more than one circuit.
Use THWN-2 14-gauge stranded wire if you get power
from a 15-amp circuit or THWN-2 12-gauge stranded wire
for a 20-amp circuit. Leave enough extra wire on each end
to reach the inside metal box plus 12 in.
The NEC requires a means, such as a single-pole switch,
to disconnect the power where it enters the shed. Photo 9
shows how to connect the switch, ground wire and neutral
wires. Run wires from the switch to a GFCI receptacle, and
from there to the rest of the outlets or lights in your shed.
