It is common practice to run electrical wiring underground. But is the practice safe? Does the gauge make a difference? The guide below will tell you.
Can You Run 12/2 Wire Underground?
Yes, you can run 12/2 wiring underground. But the gauge has nothing to do with this decision. This is what you should know:
1). You Can Run 12/2 Wire Underground If The Load Is Less Than 20A
The wire size matters because it tells you the maximum amount of electricity a conductor can safely carry. People use the gauge to identify the wire size because the unit is easy to interpret and understand.
You use the load to select the gauge. 12AWG copper lines will accommodate a 20A circuit. Therefore, you can run 12/2AWG lines underground if the load is less than 20 amps. The wire size won’t influence your decision to run the cables underground.
2). Gauge Will Determine The Length Of The Cable
The length and wire size are closely related. Longer cables have a higher voltage drop. The voltage drop is concerned with the resistance a current encounters as it flows through a medium. The resistance produces a loss of voltage.
The Spruce has given the example of a circuit that shows 120 volts when you measure the voltage at the breaker box and 114 volts when you measure the voltage at the farthest device. That reduction in voltage occurs because of the resistance.
Longer distances will produce a more significant voltage drop. Therefore, while the gauge won’t impact your decision to bury the cable, it will determine the length. Some people may bury their lines to reduce the distance they must cover to lower resistance and voltage drop.
Others may run the lines above ground because it allows them to follow the shortest path to the target. You can also choose to increase the gauge to compensate for a significant length.
3). Voltage Matters Where The Insulation Is Concerned
The voltage won’t affect your decision to bury a 12/2 line. It only matters where the insulation is concerned. Admittedly, the insulation affects a cable’s ability to survive the stresses associated with direct burial. But consumers don’t consider the voltage when they select the gauge.
How Deep Should 12 2 Wire Be Buried?
The depth matters because it affects the amount of work you have to do to install the wiring. You have four primary options:
1). Six Inches
This depth is the most appealing because it reduces the amount of digging you must do. However, six inches are only applicable if you have rugged terrain with rocky surfaces. Heavy clay soil and tree roots can also make digging a challenge.
Therefore, you can settle for six inches, but only if the wire covers a short distance. The family handyman recommends the use of galvanized rigid metal conduits, which are pretty expensive.
2). Twelve Inches
You can bury cables twelve inches deep without using a metal conduit. A UF-B line is sufficient. You can bury it directly. Some contractors use a tube to defend against physical damage.
3). Eighteen Inches
Twelve inches are suitable for 120V GFCI-protected circuits and fuses of 20A or less. Eighteen inches are more versatile. You can pair this depth with a branch circuit of any size you want. Wires in an 18-inch trench can work with ½-inch PVC conduits, which are relatively inexpensive.
4). Twenty-Four Inches
You can bury UF-B cables directly at 24 inches. Use Schedule 80 PVC for transitions from above ground to 18 inches below. Twenty-four inches are most appealing when you have granular soil. Digging is less of a hassle. You can make digging less of a chore by using a trenching machine.
The depth you use will depend on the rules in your area. The NEC expects consumers to bury UF-B cable at least 24 inches below ground. You must protect the line with a conduit whenever you expose it above ground.
This sounds like an inconvenience. But pulling UF-B cables through a conduit allows you to bury the lines just 18 inches below ground. While the NEC is the gold standard, you can ignore its regulations if your local code says something different.
Therefore, you should start by consulting the local code. Keep in mind that you need to leave the trench open until the inspector comes and scrutinizes your work. They may penalize you if the depth of the trench differs from the recommendations in the local code.
Things To Consider To Bury 12 2 Wire
The decision to bury a 12 2 wire matters because it affects the line’s ability to transmit electricity to your application safely. You must consider the following before taking action:
1). How Far Can You Run 12/2 Wire Underground?
Aim for 25 to 50 feet. 12-gauge wiring could cover 150 feet. However, you would record a voltage drop of 7.94 percent, which is higher than the 3 percent voltage drop that many experts and local codes recommend.
Voltage drop would become a problem after 50 – 75 feet. Therefore, keeping the length below 50 feet, or 75 feet at the most, would suit your needs.
The information in the chart will allow you to select a suitable length for your underground 12/2 line. If you want the wire to exceed the recommended length, increase the gauge to 10AWG.
Voltage Drop Chart For 12/2 Wire
| Watts | 20 | 40 | 60 | 80 | 100 | 120 | 140 | 160 | 180 | 192 |
| Amps | 1.7 | 3.3 | 5.0 | 6.7 | 8.3 | 10 | 11.7 | 13.3 | 15 | 16 |
| Distance | ||||||||||
| 25 | 0.1 | 0.3 | 0.4 | 0.5 | 0.7 | 0.8 | 1.0 | 1.1 | 1.2 | 1.3 |
| 50 | 0.3 | 0.5 | 0.8 | 1.1 | 1.4 | 1.6 | 1.9 | 2.2 | 2.4 | 2.6 |
| 75 | 0.4 | 0.8 | 1.2 | 1.6 | 2 | 2.4 | 2.8 | 3.2 | 3.7 | 3.9 |
| 100 | 0.5 | 1.1 | 1.6 | 2.2 | 2.7 | 3.2 | 3.8 | 4.3 | 4.9 | 5.2 |
| 125 | 0.7 | 1.4 | 2 | 2.7 | 3.4 | 4.1 | 4.7 | 5.4 | 6.1 | 6.5 |
| 150 | 0.8 | 1.6 | 2.4 | 3.2 | 4.1 | 4.9 | 5.7 | 6.5 | 7.3 | 7.8 |
| 175 | 1 | 1.9 | 2.8 | 3.8 | 4.7 | 5.7 | 6.6 | 7.6 | 8.5 | 9.1 |
| 200 | 1.1 | 2.2 | 3.2 | 4.3 | 5.4 | 6.5 | 7.6 | 8.6 | 9.7 | |
| 225 | 1.2 | 2.4 | 3.7 | 4.9 | 6.1 | 7.3 | 8.5 | 9.7 | ||
| 250 | 1.4 | 2.7 | 4.1 | 5.4 | 6.8 | 8.1 | 9.5 | |||
| 275 | 1.5 | 3 | 4.5 | 5.9 | 7.4 | 8.9 | 10.4 | |||
| 300 | 1.6 | 3.2 | 4.9 | 6.5 | 8.1 | |||||
| 325 | 1.8 | 3.5 | 5.3 | 7.0 | 8.8 | |||||
| 350 | 1.9 | 3.8 | 5.7 | 7.6 | 9.5 | |||||
| 375 | 2 | 4.1 | 6.1 | 6.1 | 10.1 | |||||
| 400 | 2.2 | 4.3 | 6.5 | 8.6 | ||||||
| 425 | 2.3 | 4.6 | 6.9 | 9.2 | ||||||
| 450 | 2.4 | 4.9 | 7.3 | 9.7 | ||||||
| 475 | 2.6 | 5.1 | 7.7 | 10.3 | ||||||
| 500 | 2.7 | 5.4 | 8.1 | 10.8 | ||||||
| 525 | 2.8 | 5.7 | 8.5 | |||||||
| 550 | 3 | 5.9 | 8.9 | |||||||
| 575 | 3.1 | 6.2 | 9.3 | |||||||
| 600 | 3.2 | 6.5 | 9.7 | |||||||
| 625 | 3.4 | 6.8 | 10.1 | |||||||
| 650 | 3.5 | 7.0 | ||||||||
| 675 | 3.7 | 7.3 | ||||||||
| 700 | 3.8 | 7.6 | ||||||||
| 725 | 3.9 | 7.8 | ||||||||
| 750 | 4.1 | 8.1 | ||||||||
| 775 | 4.2 | 8.4 | ||||||||
| 800 | 4.6 | 8.6 | ||||||||
| 825 | 4.5 | 8.9 | ||||||||
| 850 | 4.6 | 9.2 | ||||||||
| 875 | 4.7 | 9.5 | ||||||||
| 900 | 4.9 | 9.7 | ||||||||
| 925 | 5 | 10 | ||||||||
| 950 | 5.1 | 10.3 | ||||||||
| 975 | 5.3 | |||||||||
| 1000 | 5.4 |
2). What Is The Best Wire Type To Run Underground?
The wire type is more important than the gauge. The gauge tells you the conductor’s current carrying capacity. But the current carrying capacity has nothing to do with a cable’s ability to survive underground.
On the other hand, the wire type will tell you whether or not you can bury it. There’s a difference between a 12AWG NM cable and a 12AWG THHN wire. I want you to use 12/2 direct burial cables for underground installations.
This is because direct burial lines can tolerate the harmful conditions you find underground, including moisture, pressure, and pests. G&G Electric and Plumbing Distributors have mentioned additional cable types that work underground, including USE, URD, SER, and SEU, to mention but a few.
The cable type you select will depend on the purpose you have in mind. For instance, contractors use USE cables in 200-amp underground services. On the other hand, a URD cable feeds 70, 100, and 200-amp services.
In other words, the underground installation is not the only deciding factor when it comes to selecting a cable type.
3). What Is The Best Conduit?
You can use rigid metal conduits, intermediate metal conduits, liquid-tight flexible metal conduits, and rigid polyvinyl chloride conduits.
Each conduit type offers a different attribute. For instance, rigid metal conduits are strong enough to defend against physical damage. But intermediate metal conduits are thinner, lighter, and easier to install.
There is no one conduit that is best for every application. Your application’s needs will determine the pipe you choose. Consider the pros and cons of each option. For instance, galvanized steel conduits are reliable, but you need special tools to thread the pipe.
4). What Does The Code Say?
The code will place restrictions on what you can and cannot do. For instance, the NEC prohibits consumers from running NM and MMS cables through conduits in wet or damp locations. Also, the NEC wants contractors to pull individual conductors through a pipe, not a sheathed cable. Pay attention to the rules and regulations.
5). Should You Use A Solid Or Stranded Wire?
It depends on the situation. Solid wire is more robust and durable. It can also carry more power. However, it is not as flexible as its stranded counterpart. If you need a conduit, the solid wire will present a challenge.