I have a light on one side of the space under my deck, and I'd like to add another.
My plan is to add an extension box between the existing fixture and the house (using appropriate gaskets as necessary), then run UF wire out the bottom of that box using a rubber gasket, up to the bottom of the deck (which has aluminum sheeting on the bottom of it) and across to the other side, then up into the bottom of the new fixture using another rubber gasket. Both sides will have drip loops, and the middle span will be supported using wire clips.
NFPA 70 says that UF wire is permissible in wet locations, and the only provision that might prohibit its use states it may not be used "where subject to physical damage". None of this will be less than ~7' off the ground.
Does this sound reasonable, or am I going to need to put in conduit?
Best Answer
Provided you follow the same precautions as a NM run parallel to and/or through frame members, such as keeping it a minimum of 2" from the edge of the member, and secure the cable properly to the deck and walls (again, treat it like NM), this is A-OK. (You'll want to use grommets if you go through metal joists, but again, that's the same as running NM through a steel stud.)
You'll need to put in a surface-mount box for your new fixture, of course, unless it provides its own wiring space (i.e. is volume marked).