I have an interior outlet. I would like to place an exterior (GFI) outlet in approximately the same position on the outside wall. How should I do that?

approx. loc. of desired outlet-|
-------------------------------------------------------- [Exterior of wall]

------------------------------[ ]----------------------- [Interior of wall]

                        current outlet


  1. What's the best way to locate and cut the exterior hole?
  2. What's the best way to cut into the existing wiring?
  3. Any considerations for exterior mounting?

You have a fairly simple project. Assuming you intend to tap the interior outlet for power, here are the steps and materials:

  1. First, check that you have enough room in the interior outlet box to introduce one new piece of 14/2 or 12/2 NM, whichever is the same size as in the box now. I will assume you know how to make a parallel electrical junction in the interior box.
  2. Next, run that short piece of wire through a clamp in that box, across/through the wall cavity and out of a 1/2 to 3/4 inch hole in the exterior wall close by. I don't know what kind of siding you have, so I can't tell you exactly how to make the hole, but a spade type wood bit works well on many types of material. Minor fishing of the cable will be required, but not difficult, especially if the interior box can be removed partially to improve visibility.
  3. Once you have fished the wire from inside the interior box to the exterior, made your interior electrical connections and secured the cable inside, caulk the exterior hole around the wire with silicon.
  4. Feed the wire into an exterior surface mounted box using the proper grommeted fitting. Caulk around the back edges of the exterior box with silicone (to make the back water tight) and fasten it to the wall.
  5. Now you can connect your new GFIC outlet and install your weatherproof cover.

Of course, use proper safety procedures: turn off power at breaker panel before working in the interior box and doing any wire connections. BTW, if you have vinyl siding, there are special exterior boxes that will fit nicely. These are available anywhere. I know this is a long answer and maybe a bit confusing, but it is really a simple task. Good Luck

  • That doesn't sound too hard. One question though: Wouldn't it be better to run the wire to an internal housing with a weatherproof cover, instead of an entirely external housing?
    – morganpdx
    Feb 22 '11 at 19:19
  • That is an option, but you have to be absolutely sure it is water tight. A standard wall box will not work. A rain proof cover will not mate up to it. Water leaking into a wall can cause lots of problems. The type of box you are thinking of has a flange that can be caulked against the siding or has a gasket, and mates to the cover properly. Feb 22 '11 at 22:01
  • Doresoom, thanks for the edit. Looks so much better. Thank you. Feb 22 '11 at 22:03
  • Flange. Gotcha. Thanks! For the record, the siding is cedar shake. And thanks for the edit as well @doresoom ;)
    – morganpdx
    Feb 23 '11 at 18:52

Another thing to keep in mind as well is that you will need to have enough power available on your breaker. I.E. if your interior outlet is on a breaker with several other outlets and there are numerous things plugged into those outlets, depending on the amperage of the breaker for that room, it may be better to run a dedicated line. This would especially be the case if you are planning on operating any high amp drawing equipment by plugging it into the external GFI.

  • Yeah, I'm taking that into consideration. I believe the circuit is fairly underused, but I intend to confirm that first.
    – morganpdx
    Feb 23 '11 at 18:53

Just did this. A few tips:

  • Making the connections in the interior box may require more room, potentially upgrading to a bigger box.
  • Use a hammer drill if you're going through brick/mortar.
  • A PVC surface mount box for the exterior works great if you don't want to cut out a big chunk of brick or whatever your exterior is.
  • It's good to know ahead of time which direction the circuit runs. If not, test after you've broken the circuit to see which side is closest to the junction box.
  • I ran 2 wires through the wall to my GFCI, one for line, one for load. This way the outlet is in series with the other outlets in the circuit, and provides GFCI protection for those downstream outlets.
  • See note above about having enough power available on your breaker. I ran 15A, which is what everything else on the circuit uses. Fortunately I barely have anything plugged in on the circuit, so one extra outlet was no prob.
  • I saw somewhere that you should use same wire as is currently in use (same gauge). This is probably a very good thing.
  • I used UF-B wire to the outside of the house. Not sure what the difference is from interior wiring, but think UF is for underground applications. Not sure if interior wire will work going from an interior outlet to an exterior one- maybe somebody has an opinion?

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