Installing an underground power line
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Cable depth options
Underground cable for running electrical power to a remote location can be installed at different depths, depending on the type of conduit and type of wire used.
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Dig 6 inches
For a 6-in. deep trench, use galvanized rigid metal electrical conduit with individual conductors inside.
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Dig 12 inches
For a 12-in. deep trench, you can direct-bury GFCI-protected underground feeder cable with a short length of PVC conduit at the house.
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Dig 18 inches
At 18 inches, you can use THWN-2 conductors inside a continuous length of PVC conduit, which protects the wire all the way through the trench to the house.
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Dig 24 inches
At 24 inches you can bury underground feeder cable, using PVC conduit to 18 in. below ground only where the wire comes up.
If you're considering running a power lineunderground through your yard, you have four options. Your choice depends on how much power you want. It also depends on your soil type—if it's sandy and easy to dig, save money by digging deep (you won't need to use metal conduit). If it's rocky or
clay, keep your digging to a minimum.
Whichever method you choose, be sure to include a service entrance ell, which has a removable cover to give you access to the inside wires, above ground level. And get a permit and talk to your inspector about local codes before starting.
Decide how much digging you're prepared to do, which determines the type of wire you need to use. At 6 in. deep, use galvanized metal rigid electrical conduit
(1/2-in.-diameter is large enough for the water feature) and run individual conductors inside. The conductors need to be waterproof, so look for a “W” on the label, as in THWN-2. This method lets you run any size circuit. The downside is the cost—1/2-in. metal conduit is over a dollar a foot. If you have soil that's tough to dig, or you only need to run the cable a short distance, go this route to minimize digging.
At 12 in. deep, use direct-bury UF-B (underground feeder) cable, provided it meets three criteria: It has GFCI protection before it enters the ground, is limited
to 120 volts (enough for your fountain), and is protected by no more than a 20-amp fuse or breaker. We recommend this for your situation—it's only 1 ft. deep and you don't have to put the cable inside
expensive conduit. This is the best choice if you only need to power your water feature.
At 18 in. deep, run THWN-2 conductors inside PVC conduit. This method lets you run any size circuit, so it's a good idea if you want to run electricity to other items besides your water feature.
At 24 in. deep, run direct-bury UF-B cable. There's one restriction: It needs a conduit where the cable is exposed on the outside of the house and to 18 in. below the
ground. Burying the cable 24 in. requires more digging, so this method only makes sense if you have easy-to-dig soil or are renting a trench digger.