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I will install a receptacle next to a tree. I know it must be protected by a GFCI and weatherproof. But my concern is about how to support it and how high it should be from the ground.

Where in the NEC is the information about these requirements?

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  • How close to the tree? Trees not only grow up, they also grow out. The box is against the tree now, but in 20 years it could be against the tree 4 inches from where it started.
    – Tester101
    Apr 15, 2013 at 17:41

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The most important code sections to be aware of when installing outdoor receptacles, are 314.15, 314.23, and 406.8(B)(1).

First off, the box should keep water out.

National Electrical Code 2008

ARTICLE 314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures

314.15 Damp or Wet Locations. In damp or wet locations, boxes, conduit bodies, and fittings shall be placed or equipped so as to prevent moisture from entering or accumulating within the box, conduit body, or fitting. Boxes, conduit bodies, and fittings installed in wet locations shall be listed for use in wet locations.

Secondly, the cover should also keep water out even when things are connected.

ARTICLE 406 Receptacles, Cord Connectors, and Attachment Plugs (Caps)

406.8 Receptacles in Damp or Wet Locations.
(B) Wet Locations.
(1) 15- and 20-Ampere Receptacles in a Wet Location. 15- and 20-ampere, 125- and 250-volt receptacles installed in a wet location shall have an enclosure that is weatherproof whether or not the attachment plug cap is inserted. All 15- and 20-ampere, 125- and 250-volt nonlocking receptacles shall be listed weather-resistant type.

Lastly, you'll want to make sure the thing isn't laying in the mud. Depending on the Authority Having Jurisdiction (AHJ), you might get away with attaching the box directly to the tree, or supporting it with the conduit used to supply it. The proper way to do it, however, would be according to 314.23 (B). Use a stake.

314.23 Supports.
(B) Structural Mounting. An enclosure supported from a structural member of a building or from grade shall be rigidly supported either directly or by using a metal, polymeric, or wood brace.

(2) Braces. Metal braces shall be protected against corrosion and formed from metal that is not less than 0.51 mm (0.020 in.) thick uncoated. Wood braces shall have a cross section not less than nominal 25 mm × 50 mm (1 in. × 2 in.). Wood braces in wet locations shall be treated for the conditions. Polymeric braces shall be identified as being suitable for the use.

Common sense says you should install the box up out of puddles, and if you get snow in your area above the normal snow level. There are no code sections that deal with the height above grade, so use your best judgement. And never forget the most important code section of all...

110.12 Mechanical Execution of Work. Electrical equipment shall be installed in a neat and workmanlike manner.

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When positioning the outdoor receptacles in the landscape, it is important to position them vertically. Horizontal positioning will allow water to penetrate, increasing the likelihood of a short circuit. The bottom part of the receptacle should be at least 6" off the ground. When positioning the receptacle be sure that it is at least 6" above any mulch or other ground covering as well.

http://www.doityourself.com/stry/lightoutside#b#ixzz2QAionRz9

As for mounting the outlet box, I would probably drive a 2x4 or 4x4 post into the ground below your frost line and secure the outlet box to that.

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  • Any wood in contact with earth should be decay resistant or treated. Over sized rigid conduit would also be adequate support, though if it's considered a structural support it would be a code violation. I see it as unsupported conduit simply supporting itself, non-structural, but this may be wishful thinking.
    – bcworkz
    Apr 11, 2013 at 19:53
  • @bcworkz - What if one normal size conduit brings the wires to the receptacles and then a separate oversized one becomes the support. Does that solve the "fuzzy problem". BTW using rigid conduit in the ground has also a rusting problem that over time can render the support ineffective.
    – Michael Karas ♦
    Apr 12, 2013 at 12:34
  • @Michael Karas - That would work in my book, but interpretation is ultimately up to the inspector. Fair point about rust, but one could use rigid non-metallic conduit. The larger size required for weaker PVC material would mean the wire containing conduit, EMT, or whatever, could be coaxial with the support "conduit", which could actually be water pipe for all that it matters. The main appeal to me is the tidy appearance of having the box threaded directly onto the support.
    – bcworkz
    Apr 12, 2013 at 19:33
  • Poppycock! Orientation of the receptacle doesn't matter. Height above grade doesn't matter (if installed properly).
    – Tester101
    Apr 15, 2013 at 18:28
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I think it depends on what "code" means in your parts. Worst case scenario is you get electrocuted again.

Kidding aside I run outdoor rated cabling inside of PVC. Yes water will get in PVC but moles won't and you won't dig through the pvc.

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