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Feeder panel for workshop

QuestionI 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?

AnswerMy 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!

Copyright © 1999 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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C.R.S., Inc. · Spokane, Washington · USA

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