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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

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    How deep do you want to bury it? – Harper - Reinstate Monica Jan 2 at 19:14
  • Wouldn't it have to be at least 18", if it's not in a conduit? – SteveSh Jan 2 at 20:03
  • I’m ok burying to 18 inches (I say now that I haven’t started digging)... in which case it’s ok to use THHW wire and PVC conduit? THHW a special version or romax? – user903805 Jan 2 at 21:35
  • Wouldn't be a bad idea to familiarize yourself with burial cover requirements found in NEC Table 300.5 icmag.com/ic/picture.php?albumid=3742&pictureid=55224 – NoSparksPlease Jan 3 at 1:42
  • Where in the world are you ? – Criggie Jan 3 at 6:19
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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.

  • THHW a special version of romax? – user903805 Jan 2 at 22:02
  • @user903805 No, it's just a standard single wire sold in your home store or electrical supply store. The THHW refers to the insulation type, this being moisture and heat-resistant thermoplastic, good for 167 degrees F for wet locations and 194 degrees F for dry locations. You would need three of them: black, white and green. It's meant to be pulled in conduit. – JACK Jan 2 at 22:25
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    Note that you won't find THHW at your home store -- the wire sold there is THHN/THWN-2, instead (which is acceptable) – ThreePhaseEel Jan 3 at 1:18
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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.

  • I do not expect to pull very hard on the outlet, no power tools. 300watt low voltage transformer for 12v lighting and then LED Christmas lights, maybe 2-4amps max – user903805 Jan 2 at 22:02

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