I have 2 of the following round boxes at my home hidden behind a cover:

round box with wires

Now I'd like to mount an outlet on it, and I'm trying to understand what the right things to use are.

To my understanding, this box is too small to house any kind of outlet, so I need to mount a box in front of it, like this one, and then mount the outlet and cover on that box.

Is that the right way? (And what is the purpose of those 2 metal plates inside of the box?)

  • That looks like a lamp was mounted to it previously. The wires running to it may not longer exist, depending on when and how and why the fixtures were removed.
    – keshlam
    Commented Apr 26 at 19:29

1 Answer 1


The best way would be a single-hole round weather-proof cover, with the addition of foam and/or silicone sealant to help it seal against the rough surface.

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From there, a 90 degree connector and a short length of flexible weatherproof conduit to the box that you linked.

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Buy black, white and green loose wire (THWN #14 or #12, to match what's there, enough to run through the conduit with 6 inches extra at each end), connect to the existing wires at one end and to the outlet and box ground lug at the other. You'll also need an outdoor outlet cover to put on your new box. YOu can buy one in a kit with a GFCI outlet.

Mounting your outlet box directly over the round box in a weather-proof manner will be difficult and kludgy.

The two metal plates in the back of the box are strain relief clamps. You can see the bottom one holding the cable to the box.

  • OP will also probably need to add extensions to the wires to have the needed six inch of wire for the outlet.
    – crip659
    Commented Apr 26 at 19:57
  • @crip659 I did not intend that existing wires should run through the conduit to the outlet. I'll clarify.
    – jay613
    Commented Apr 26 at 20:00

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