Join Date: Apr 2007
Location: St Thomas USVI
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Re: Adding GFCI Outlet: Looking for Surface mounted back box
I wouldn't get too hung up on UL ratings but would look for NEMA ratings instead.
The requirements of an electrical box are to contain potential arcing and heat to prevent the spread of a fire. In your case, mounting a device (GFCI) receptacle is also a requirement. By it's very nature, flammable materials, like wood, do not make sense for containing potential electrical faults or fires. There are some polymers that do meet NEMA standards that are non-metallic. Carlon, Panduit, and Hubbell some brands that come to mind. Any electrical retailer near you should have something that will work. You can also look at Grainger. I believe they have an online catalog.
You could always put some teak veneer over the outside of whatever box you choose.