Feeder panel for workshop
I want to run electric
to a storage shed in my backyard. The distance from the house to
the shed is 235 feet. I plan to use the shed as a small workshop
with lights and outlets for 120 volt equipment, such as small saws
and hand tools. I already have conduit from the house to the shed.
Can I add a breaker to my 200-amp service and run a number 10-2
cable from the breaker box to a breaker box in the shed adding a
ground at the shed?
My first advice—since I am not a licensed electrician—would
be that you hire someone who is so that the final results meet electrical
codes in force in your area. If you choose to do the work yourself,
you need to check with your local building department and acquire
the necessary permits for this work. That said—and to answer
your question—it depends on how big the shed is and what you plan
to do with the power. There may be a voltage drop due to the distance
and this would affect motors more than lights, however, a larger
gauge wire could eliminate that problem. Figure that No. 10-2 with
ground wire will provide about 30 amps on a 220/240-volt circuit,
No. 8-2 with ground wire will provide about 40 amps on a 220/240-volt
circuit, and No. 6-2 with ground about 50 amps on a 220/240-volt
circuit. If you are going to have a woodworking shop (as you've
mentioned) or an automotive shop, then you will need a subpanel,
which is basically an extension of your main service panel. If this
is the case, you need to know the load. For example, if you plan
to use a welder, what is the required amperage for the unit?
Three types of installation can be done at the storage shed:
1. The first is a single circuit—the wire is connected to
a single circuit breaker in the main service panel and the other
end of the wire runs to a disconnect switch (light switch) near
the door so all power can be shut off at one location. The disconnect
switch cannot be more than 15 feet from the point of entry. Outlets
need to be a minimum of 18 inches above the floor and must be
ground fault circuit interrupter (GFCI) protected for safety.
If any of your tools short out, the GFCI will protect you from
shock. A single GFCI outlet breaker can protect several outlets
downstream (check the manufacturer's installation guide).
2. The second is a feeder panel. This connects to a 220/240-volt
circuit breaker or a pair of breakers (amperage depends on the
load you anticipate) in the main service panel. It then feeds
the subpanel that, in turn, feeds the branch circuits in your
shed (lights, outlets, switches, etc). Three wires may be run
from the house to the shed, two hot and one neutral to the subpanel.
The subpanel shall be listed as a service equipment panel and
the main disconnect cannot be more than 6 1/2 feet above the floor.
There must be clear floor space a minimum of 36 inches in front
of the panel. The neutral bar in the panel shall be bonded to
the panel according to the manufacturer, and the panel shall be
bonded to two 8-foot ground rods driven into the ground a minimum
6 feet apart. Then wire the shed with circuits as you need. If
the shed has garage doors, it will be considered a garage.
3. The third is full service from the utility with a panel, which
requires two 8-foot ground rods a minimum of 6 feet apart. Then
run circuits as described above.
Finally, how do you plan to run the wiring to the storage shed—overhead
or in the ground? Overhead you will need some type of entrance head
and will need supports under the wires or support cable and hot
wires mounted so wiring in its lowest spot is not less than 12 feet
off the ground and 18 feet over a driveway. Underground you will
need two long bend (LB) 90-degree elbows (they will keep the conduit
close to the buildings), one for leaving and the other for entering.
For example, if you are going in the ground, then run a cable from
the main service panel (not connected) to a junction box at the
rim joist. From the junction box an LB 90-degree elbow and conduit
can be used to run the wire below grade. If you are using direct
burial wire UF (Underground Feeder) or USE ( Underground Service
Entrance cable ), install a long sweep 90-degree elbow to terminate
24 inches below grade. Run the wire a minimum 24 inches deep to
the storage building and repeat the conduit and fittings to enter
the storage building. If you are going to run conduit (as you've
already done) from the house all the way to the shed, install a
long sweep 90-degree elbow to straighten out the conduit a minimum
of 18 inches below grade unless it is rigid steel (Schedule 40),
then it can be 6 inches below grade. When using conduit, wires to
be pulled need to be individual wires and not a cable assembly.
Because of friction on your length of run, you may need a pull station
or junction box near the center of the conduit.
A word of caution: the main service panel you will connect to is
a "live" box! Utmost care should be exercised while in this box
and that the wires connect to the correct breakers. Treat the white
wire as a "hot" wire: identify it by putting black electrical tape
on the ends and connect the black and white wires to the breakers.
Connect these wires while the breakers are "off" in the main house
panel. All wiring work, until you get to the feeder panel in the
shop, should be done with the circuit breakers in the off position
or wires should remain disconnected from the circuit breakers until
all connections are made. At the junction box, the cable from the
panel will tie to the wires that are pulled in the conduit, black
to black, white with a black marker to a black or red wire and the
ground to either a bare or green insulated neutral/ground. Finally,
do not stand on a damp floor while you are working in the panel
box. Protect yourself by wearing rubber gloves and rubbers and stand
on a rubber mat or a piece of dry wood. If you are uncomfortable
working in the main service panel, hire a licensed electrician.
You can dig the trench—and in your case it appears that you
have already done that!
1999 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.
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