Run 50ft underground electrical: gauge and conduit?

Question

I have a gfci outlet in my garage, only thing connected to a 20amp breaker (it’s about 20ft from the electrical box). I would like to add an outlet 50ft outside in my flower bed.

Two questions:

1. What size and type wire should I run? I have read about direct burial cable but not sure the size. Going to be installing a low voltage transformer at the end and Christmas lights, so not to much pull.

2. I’m worried about installing direct burial cable without a cover, even at 18 inches down it scares me. Can I run it inside pvc conduit?

Thank you

Answer 1

A 20 AMP breaker you can run #12 but if you're going to install the PVC conduit, use 3 #12 THHN/THWN-2 wires, black, white & green. You don't need the direct buried cable when using conduit. If you can feed it from the box your existing GFCI is in, then you could connect to the load terminals of it. If you're connecting elsewhere you'll need a GFCI outlet at the termination of the run. 1/2" conduit will be right for your job. Stay away from using backstabs and if you use stranded wire get heavy duty outlets with the screw back clamps.

Answer 2

Yes, you can extend off the LOAD terminals on your GFCI (Hot+neutral from LOAD, ground from the pigtail splice).

How hard do you expect to use this outlet? If you're using ordinary tools up to about 1900 watts, then 12 AWG wire will be fine. If you expect to max out the 2400W capacity of the circuit on a regular basis, then you are just on the cusp of distance calling for a wire bump, so I would use 10 AWG.

If you want to bury with 24" of cover, you can use direct burial cable such as "UF type". This looks roughly like common NM/Romex, except is gray, and the wires are different and contained differently.

If you want to bury this with 18" of cover above it, you can use PVC conduit. Check the requirements for which segments need to be Schedule 80; particularly where it emerges from the ground and may be subject to physical trauma. Schedule 40 is pretty fragile. They fit together, but Sched 80 has less inside diameter and can hold fewer wires. Three #10s will be fine though.

If you want to bury with 6" of cover above the pipe, you can use Rigid metal conduit (literally RMC; water-pipe-style stuff; I don't just mean any metal conduit that is non-flexible). The stuff is stupid pricey, but on the other hand, you can trench it with a garden trowel. You will need to make a trip or two to the hardware store to have them cut and thread your pipes.