Installing an underground power line
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.