So I am in the final stages of a deck rebuild, and at the last minute thought about a slight change.

To the right of this photo you can see an power outlet on the wall, currently has a yellow extension cord plugged in.

Behind the photographer, the deck runs for another 20 feet to the end of the yard. I'm thinking it might be useful to have power at both ends of the deck (for a bug zapper or fan) so need to run some wire for this.

My plan is to run some PVC conduit that goes to the gang box pictured, under the deck and then 'pop up' at the other end of the deck (where a second GFCI outlet would be installed in a outdoor box). The conduit will NOT be buried, but rather fixed to the underside of the deck.

Any thoughts on this approach? I'm concerned with the following:

  1. Having a junction box outside (i.e. using the gang box with the outlet as a junction)
  2. Not having the cable buried. Everything I could find online suggests outdoor cable should be buried.
  3. Bridging two GFCI outlets

Photograph of outlet

  • What are your concerns
    – Tester101
    Jul 11, 2016 at 19:51
  • Sounds good under the deck only schedule 40 would be required, if the feed to the new outlet above the deck is exposed schedule 80 would be required
    – Ed Beal
    Jul 12, 2016 at 0:59
  • Concerns updated in the original message, thanks for asking!
    – Levi
    Jul 12, 2016 at 17:09

1 Answer 1


The first problem can be dealt with using a Bell 5403 or equivalent weatherproof extension box to provide a place to hook the conduit to and some extra cubic inches for the additional wire fill. You'll need to hook a ground pigtail to it, by the way -- there do not seem to be non-metallic weatherproof extension boxes.

Since you are running conduit under the deck -- you can run individual THWN wires inside it instead of a UF cable (although running UF aboveground is permitted when protected from physical damage and direct sunlight if it isn't IDed as sunlight resistant), and running THWN will make it easier to pull even with an oversized conduit -- 3/4" inch will provide ample space for a single circuit extension like yours. Don't forget to put in expansion fittings, lest your conduit run do the snake on you!

Last but not least -- simply use an ordinary outlet for the new outlet, and run it from the LOAD terminals on the existing GFCI. (Although putting two GFCIs in series won't break anything, it could confuse you as there is no guarantee as to which one will trip when something happens.)

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