Answer: You can repair an outdoor light fixture mounting problem sometimes by using a siding box. They are available in a few styles to accommodate various sizes of siding on the house.
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Below are photos from a repair of an outdoor light fixture with a funky electrical box mount that I corrected for a client by using a siding box.
When I first saw the above outdoor light fixture mounted this way I had no idea what to expect. I had to use my razor knife to cut into the white blob behind the outdoor light fixture and discovered duct tape beneath.
The outdoor light fixture was attached to the outside wall using a metal, surface-mounted, indoor, octagonal electrical box that was wrapped in duct tape and covered in caulk. This was not a good method for attaching an outdoor light fixture to a building.
Normally a pancake electrical box would be mounted to the surface of the Oriented Strand Board (OSB) sub-surface and the outdoor light fixture would be attached to that. The vinyl siding would be cut around the pancake box.
Though a pancake box is shallow, the National Electrical Code (NFPA 70) approves its use because the cubic inches of space inside of the outdoor light fixture canopy (Indoor light fixtures also) is allowed to be included when calculating the number of wires permitted.
However, a pancake box does not always provide a good solid-level surface to support the light fixture. This varies by the surface of the wall of course.
The octagonal indoor electrical box had two of its knockouts removed and was covered with duct tape and caulk. In addition to being awkward looking, it was clearly not an approved weatherproof arrangement, even with the caulking.
The old metal box was not grounded as required in Article 250 in the National Electrical Code (NFPA 70).
My guess is that there was a pancake box installed originally when the townhouse was built, but for some reason, it was removed. I had to use a razor blade scraper to remove the bulk of the caulk that had adhered to the vinyl siding.
Fortunately, the type NM electrical cable was in good working condition. I removed the two-screw metal clamp-type Romex connector and used the plastic button-type connector packaged with the new Arlington plastic siding box that I installed.
A siding box is an excellent method of supporting an outdoor light fixture on vinyl siding and other surfaces. I have used them many times to repair an outdoor light fixture installation.
In addition to siding boxes, there are also siding blocks available that do not contain a built-in electrical box. Siding blocks work with other electrical boxes to help level and trim outdoor light fixtures.
FINISHED REPAIR OF AN OUTDOOR LIGHT
The #8141DBL siding box keeps the light fixture level and helps to prevent it from indenting the vinyl siding.
The siding box used to repair an outdoor light fixture here is made by Arlington Industries.
Click here to see another example of an exterior light fixture wiring repair where I had to pull in new wiring.
My post about light switch wiring diagrams may be helpful when doing this type of work.
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