How Far Can You Run A 10-Gauge Wire?

You have your new shop or utility shed built and ready to go. Part of the plan is to run electrical service to the new structure from your home. However, the question of what size wire is required to get electricity to your new utility shed. What kinds of distance can you get if you use 10-gauge wire?

According to the National Electrical Code (NEC) Section 310.15, the maximum distance to run 10-gauge wire carrying 120-volts at 20 amperes is 85 feet. This calculation is based on the NEC recommendation to allow a three percent voltage drop. If you install a 15-ampere circuit using 10-gauge wire, you can increase the distance to 115 feet.

Several factors affect the distance that you can run 10-gauge wires safely. You must be aware of the factors and limitations imposed by the electrical codes before installing a branch circuit at a long distance from your service panel. Failing to understand these limitations can put your project out of code compliance and put your home and family at risk.

You can find tables and charts with suggested maximum distances to run a given wire size. These charts and tables generally assume the electrical load and other variables. In theory, the actual calculations underlying the charts and tables should be used to determine the distance you can run a wire.

These calculations take into consideration several variables that affect the distances. The type of wire, the wire material, the maximum load at the point of use must be considered. The National Electrical Code gives details of these variables and the calculations to determine the proper wire size.

To better grasp the science and math used to determine how you can run a 10-gauge wire, let’s look at an example electrical installation. We will assume you are running a new branch 20-amp circuit to a craft room, for our example. The craft room is adjacent to your existing garage and about 30 feet from the service entrance panel.

A little preliminary work is in order before any wire is pulled, circuit breakers are installed, or outlets are in place. The first thing is to determine how much electrical power you will need in your new addition. Here are some typical uses of electricity in a craft room.

Most residential branch circuits are wired with 14-gauge or 12-gauge wires. On 15- or 20-amp circuits, these wire sizes give you plenty of capacity to meet the minimum code requirements. However, when the overall length of the branch circuit wiring goes above a certain amount, an increase in the size of the wire is necessary.

Looking at the common capacity of residential circuits is crucial to understanding the problem. A 15-amp 120-volt circuit can deliver 1,800 watts. Typically, the number of outlets on a 15-amp circuit is eight. This keeps the current draw, in most cases, below the 80 percent capacity of the circuit breaker.

1,800 watts times 80 percent = 1440 watts.

Eight outlets’ times 1.5 amps per outlet at 120 volts = 1,440 watts

Don’t forget to figure out lighting and other accessories on the system.

The calculated voltage drop shown in the table above is based on a 120-volt branch circuit at one amp load and a power factor adjustment of 0.85. If you are running an electric iron that draws 12.5 amps, the effective loss to resistance using 14-gauge wire at 70 feet would be 4.75 volts. This would reduce your effective line voltage from 120 volts to 115.25 volts.

Your appliances may be able to run at this reduced voltage. The danger is the heat built up in the electric wires by the resistance. This resistance can also cause breakers to trip. It would help if you also remembered that resistance is cumulative. Any other appliances or lights that are working simultaneously add to this resistance and resultant voltage drop.

In effect, you can reduce the effect of resistance in a branch circuit by increasing the wire gauge up to a point. Long wire runs require careful planning and evaluation to determine the appropriate wire size for the line.

If your electrical project includes adding a branch circuit for an addition to your home, the problems with using 10-gauge wire may be minimal. However, other factors enter the equation if you are running a branch circuit for some distance to a utility shed, workshop, or detached garage.

How will you extend the branch circuit to the remote location? There are only two options. You can hang the wire above ground or bury the wire below ground. Both options entail more work and many restrictions to consider.

Above ground, wire installations are governed by the electrical codes and require a minimum height above ground. The electrical code also specifies what wires are required for above-ground installations. This is especially true of suspended electrical wires that cross inhabited areas. Codes vary by location, and you should consult with your local building inspection office before making an above-ground electrical installation.

Going below ground is, in some cases, less trouble. Only specific kinds of electric wire are rated for direct burial. Some jurisdictions mandate that buried electrical cables be inside an appropriate conduit or raceway. The depth of the trench is also a consideration, as is digging the trench to avoid other underground utilities.

Suppose you anticipate that part of your electrical wire installation will be underground. In that case, we recommend that you consult with a professional with experience in underground wiring rather than performing the task yourself.

When planning a long wire run using a 10-gauge wire, there are some other considerations. Most residential electrical equipment such as duplex outlets, light switches and GFCI outlets are designed with 12- or 14-gauge copper wire. Moving up to 10-gauge wire can present some difficulties.

If you elect to run 10-gauge wire at a distance, be prepared for more labor. Most 12- or 14-gauge residential electrical fixtures are sized for these wire gauges. Most new outlets and some electric switches come with Stab-Lok connectors that are quick and easy to use. However, these quick connectors will not work with 10-gauge wire. You will need to bend and install the wire on standard screw terminals at each outlet and light switch.

Running 10-gauge wire through a structure can be quite a task. The larger wire doesn’t bend as easily, making wire runs more challenging. Getting the wire to where you need it can be frustrating under some circumstances.