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When I replaced the GFCI in one of my exterior receptacles, I found that the installer had simply drilled a 3/4" hole through the house's wall and fed the cable through it and through the threaded opening in the back of the electrical box:

Exterior electrical box

What should I use to secure the cable where it enters the electrical box? I'll be re-applying caulk around the electrical box when I'm done; is there anything else I need to do to seal the hole in the wall (3/4" seems excessive for a single 12/2 cable)?

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up vote 9 down vote accepted

What you see is very common, no RX connector. I think you will find that a common $0.50 3/4 inch romex (NM) connector will screw directly into the treads of the knock out.

RX connector

Simply remove the tork nut and thread the connector into the box hole threads. This will work fine with the back hole since your going to seal the box to the wall with silicon. If you were to use the side, top or bottom knock outs, or not otherwise give the opening a water tight seal, you would have to use water tight connectors for the wire size.( rubber insert for 12/2, 14/2 UF/NM Etc.

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