I agree with the above, you either hit the structure inside or you have trouble with anything more than the smallest raceways and boxes.

In a pinch I have used toggle bolts on this with a fender washer to cover the hole. A little spray paint that is a close match hides the washer pretty well compared to leaving it shiny zinc.

This is a poor option if you can see it from inside the building though. [Linked Image]

If I had to do that job in the picture (with the right boxes) I would probably use at least four #12 fasteners and a full layer of silicone adhesive between the box and the wall.

Bob

Bob Badger
Construction & Maintenance Electrician
Massachusetts