What Size Wire to Run to a Shed?

When I built my first shed years ago, I decided quickly that I need electricity for some lights and use my tools. Wiring the inside of my shed was easy, but I wasn’t sure what size wire to run to a shed.

The size of the wire you run to your shed depends on how far away it is and whether you use 120V or 240V. If your shed is 50 feet from your breaker box, you can use 10/2 AWG UF-B wire for a 120V circuit up to 20A. This will allow you to run multiple machines at the same time while providing light to your shed.

The above circuit will provide plenty of power for some lights and a couple of 120-volt outlets. If you are looking to power some heavy equipment, such as a welder, then you’ll have to upgrade to a higher amperage breaker and a lower gauge wire.

Below we’ll take a look at all your options for using different sizes of wire, including wire types, gauges, and conduit.

What Size Wire to Run to a Shed

Most shed owners need a couple of outlets and some lights to see what they’re doing. Typically the most amps you’ll need are a little over 15 to run your lights and a miter or table saw simultaneously. Use a 20 amp breaker and 10/2 AWG UF-B wire.

Here’s why: a 20 amp breaker will ensure you don’t trip your breaker when operating your tools and lights at the same time. Heavier equipment like a miter saw is rated up to 16 amps. While that doesn’t mean that it will operate at 16 amps all the time, it does indicate that it can get close to it. Thus, when combined with lights, then a 15 amp breaker is not enough. Go 20.

Typically in your house, you’ll use 14 gauge wire with your 15 amp, 120-volt breakers, and 12 gauge wire with your 20 amp, 120-volt breakers. So why not just use 12 gauge wire to run to your shed?

Using 10/2 wire for your shed will allow you to upgrade to a 30 amp breaker in the future. This saves you from removing the 12 gauge wire from the conduit and then fishing new wire back through the conduit.

If you are dead set that you’ll never want to upgrade your amperage – which would allow you to run an electric heater plus power tools – then 12/2 AWG UF-B wire is perfectly fine. The wire is the appropriate gauge for a 20 amp breaker.

What Wire to Use for 240 Volts

Bringing 240 volts to your shed means that you want to operate something like an electric fireplace or welder. If this is the case, you’ll need either a 50 or 60 amp breaker in your main subpanel.

Use 6/3 AWG UF-B wire will allow you to bury it directly into the ground, and is a low enough gauge to safely supply power for your 240-volt circuit in the shed.

If you are going to be using lower-rated 240-volt devices, such as a window air conditioner, then you can use a 30 amp, 240-volt breaker in conjunction with 10/3 AWG UF-B wire.

Last – always be sure to check the voltage requirements and total wattage of the device you intend to use. Remember the old formula – volts x amps = wattage. Not all devices are created equal, so while your neighbor might run a power tool on a 15 amp circuit with 14/2 wire, it doesn’t mean you can. Always read the labels first.

What Wire Size to Use: Examples

The longer the circuit, the less ability that circuit has to provide voltage – this is called “voltage drop”. Wire releases heat, which is essentially electricity loss. The longer the wire, the more heat that is lost.

If you run wire to a shed that is far from your house, you might experience the results of voltage drop – tools that don’t run up to maximum power, dim lights, etc. That’s because your 120-volt circuit is more like 108 volts…or less!

One way to compensate is to get thicker wire, which will lessen the resistance of the current and reduce voltage drop. Remember, the thinner the wire, the more resistance – and heat loss. Make the wire thicker, then you get less resistance.

Let’s take a look at the size of the wire required for running a circuit to your shed from your main panel in your house.

Note: the following calculations are in line with national regulations that stipulate a 3% voltage drop being the maximum allowable loss in a circuit.

• 150 Foot Run – A 120-volt circuit on a 20 amp breaker will require 6/2 AWG wire for 150 feet.

Above, we mentioned that your shed should use a 10/2 wire when running power from a 20 amp breaker to your shed for 120 volts. However, that will only work if your shed is 85 feet or less from your breaker box.

A 150-foot, 240-volt circuit running on a 30 amp, the double-pole breaker would need 8/3 AWG wire supplying the shed from the breaker box.

• 300 Foot Run – a 120 volt, 20 amp circuit would require 4/2 AWG wire. A 240 volt, 30 amp circuit would require 4/3 AWG wire.

• 500 Feet – a 120-volt, 20 amp circuit would require 1/0 AWG wire. A 240 volt, 30 amp circuit would require 3/3 AWG wire.

Keep in mind that a 3% voltage drop is minimal. If you were to use 8/2 wire for a 150 foot run to a shed on a 20 amp breaker, chances are you wouldn’t notice the drop. Why? You’d have to be running multiple machines at once on full power to achieve 20 amps.

While I don’t recommend going over the 3% voltage drop parameters, understand that many people will use a higher gauge than dictated by a voltage drop calculator and see no difference in the performance of their power tools or devices.

What Happens If Wire Gauge Is Too Big?

You’ll come to find when you go to your local home reno store that wires come in all shapes and sizes. You might be tempted to overcompensate when wiring your shed. For instance – what if you take up welding or put in an electric furnace in the future? You’ll need a larger wire.

Therefore you don’t want to shell out for a wire that might be adequate in the meantime but not adequate for future needs. Can you simply put a larger gauge wire with a lower voltage and amperage circuit?

Can I Use Oversized Wire?

Yes, you can use a larger, oversized wire with a smaller circuit. You won’t see any decrease – or increase – in performance of the circuit.

The only benefit is that you will reduce the voltage drop in the circuit – although it will likely be negligible in the first place.

You don’t want to supply 240 volts to your shed and then discover you need 6/3 and not 10/3. There is no harm in using a lower gauge of wire when a higher gauge will suffice. It gives you room to expand without having to replace the wire.

The benefits of using a larger gauge of wire include:

• Gives your room to increase the amperage of your breaker in the future without changing wire size
• Reduces the voltage drop in the circuit, improving the ability of devices on your circuit to perform at max power

What If My Wire Size is Too Small?

Using wire that is too small for the circuit could result in damaged devices, burnt wires, or fire. For instance, the use of 14 gauge wires on a 20 amp circuit will result in too much resistance within the wires. This will manifest itself in excessive heat, which could melt wire insulation and cause a fire in your house or shed.

At the very least, the wire insulation can melt slowly over time and cause a shock hazard. If it is near insulation or something else that is flammable, then you have an extreme fire hazard.

What Size Breaker Do I Need for a Shed?

A shed requires different considerations than a house when considering power supply needs. Your shed will see less frequent power usage, but when it is used, the wattage of the devices operated will be much higher. Saws, compressors, grinders – they all use serious watts.

Therefore, wiring your shed for 15 amps is a mistake. You may not be able to use a miter saw and a light at the same time, for a more powerful miter saw.

Use a 20 amp breaker with the wiring recommended above, and you’ll be able to power multiple tools and lights all on the same circuit.

If you need 240 volts in your shed for a larger device like a welder, it depends on how many watts the device will need to use. A 30 amp breaker will suffice for 240-volt appliances like a window air conditioner. A 60 amp breaker will likely be required for a welder.

How Far Can You Run 10 Gauge Wire?

You can run a 10 gauge wire up to 85 feet on a 20 amp circuit. If you opt to use this type of wire on a 15 amp circuit, it can run up to 115 feet. After these distances, the circuit will go over the recommended 3% voltage drop.

You can run a 12 gauge wire up to 70 feet on a 15 amp circuit. That number drops to 50 feet if you run 12 gauge wire on a 20 amp circuit.

Can I Use an Extension Cord to Power My Shed?

Yes. But I would not recommend using an extension cord to power your shed as a permanent solution.

While this is a quick and easy fix for getting power to your shed, the dangers of having an extension cord permanently sitting between your house and shed is not a good idea, and here’s why:

1. It could break, rip, or tear.
2. It’s a hazard to others in the yard.
3. It’s inconvenient if you want to plug in more than one device.
4. You can’t light your shed and use a tool at the same time.

Do I Need to Bury the Wire?

Yes. The only type of wire you are allowed to use outdoors is wire with the acronym “UF”, which means “underground feeder”. You can usually bury this type of wire either directly or in a conduit.

If you choose to bury the wire directly in the earth, then you’ll have to dig down 24 inches. If using conduit, 18 inches is enough.

If you are only running one circuit to your shed, then you won’t need a subpanel. You will, however, need a shut-off switch where the power enters the shed. This can simply be a light switch that controls all outlets and fixtures in the shed.

With more than one circuit, you need a subpanel, which can be found in this article explaining how to run electricity to a shed.

Conclusion

Whenever you are dealing with electricity, safety is of the utmost priority. Make sure you power off your main shutoff breaker when installing a new breaker in your box. Connect newly installed shed wiring to the breaker box last, so you don’t risk a shock when installing the wiring or receptacles.

Wiring can be confusing, and I hope this article was able to clear up any questions you had about what size wire to choose for your shed. Remember, never take a chance or guess with electricity. If you are still uneasy about wiring your shed or choosing a wire size, consult with an electrician.

As always, thanks for taking the time to read this article. Please drop me a line or comment below if you have any questions or want to share your own experiences choosing a wire size for your shed.