When the plumber has installed his vent pipe going up the wall for the sink directly in the center of the sink, how do you put a light box there, when there's not enough room in the wall for a cut in box?? Thanks....

Sparky:

Depending on the fixture, and what if any flexibility there may be in the wiring entry point you may not need the box in the center. Best solution IF the fixture has to go dead center....guess who has to move the vent pipe.

Use a pancake box.

Absolutely a time where prior planning makes ALL the difference.

Yup, I've yet to meet a plumber who didn't insist that his vent had to go absolutely straight up the middle, centered on the sink.

Best option? Convince the customer to use a long 'light bar,' one long enough to cover your off-center box.

Pancake box attached to a metal hanger between the studs might work as well.

Stupid question time: Do we really need a box? Can't the light fixture be considered the 'box?' Let's see some code on this issue.

How do you use a pancake box without screwing it to the vent pipe. I realize the vent pipe normally has no water in it, unless it's melted snow or rain coming in from the roof, but even if you do mount it to the vent pipe, it sets back in the wall about 1" or so, making a big gap in between the box and the sheetrock, not to mention the long screws that would be needed to mount the hanging bar. If the vent pipe is off center just a little bit, it makes it worse, because then you can't get a cut in box in, and not a centered surface to mount a pancake box.... Any other ideas. This is an old problem for me and very aggravating. It would be good if the plumbing code wouldn't allow this. Maybe I could put in a request for their code panels to look into this

It depends on the luminaire and how it is listed. There is no reason a self contained light couldn't just have a romex connector in the back. I am just not sure I have ever seen one

Reno, just saw your post.
#1. Doing it on the rough may be one answer if you dare to nail up a light box and think it will actually be in perfect center on the trim. I'm a little learious of doing that. I prefer to leave my wire in the wall and center it on the trim.

#2. Trying to get the plumber to change his vent pipe is like pulling bird teeth (normally ain't going to happen)

#3. When remoldeling neither of the above is an option

#4. A pancake box on a piece of metal stretched between studs might be alright when the wall is open, but again, not an option on remoldel work

Still think the plumbing code needs involved in this....

One more thing.. I'm talking about a light fixture that needs a box to mount with where the canopy is round and not one of those long 3 or 4 etc..bulb type
Thanks..Steve...

If it is a small fixture with a standard canopy, I use a surface-mounted pancake box with toggle bolts. The screw holes in the back of the box are far enough apart to span a 1-1/2" pipe which is most likely to be all that you will encounter.

If it is a strip or bar light with a solid back, I just use a Romex connector. If there's not a KO near where it needs to be, I just punch one.

I do it about the same, except I always put a backer between the studs to mount the box on, with the top of the backer at the centre of the light. There is always room for something, even plywood, to cover about half the box. Worst case would be to get behind the sides of the box. Then, you can cut the pan box in after and have something to screw to.

I got burned by a vanity that was a different size than drawn and a mirror that made it obvious that the light wasn't centred.

You can use a pancake box. To support the pancake box, use a 11/2 wide by 8" 1/2 thick strip of plywood. Use construction glue on 2" from each end. Insert the strip in the hole, centering it, so the glue sticks to the back side of the drywall. Use another strip of equal size with a screw in the center to hold the strip in place till the glue is dry. When dry, unscrew the second strip and screw your box in place. You can also use drywall screws on each side of the box opening to hold the strip in place if the fixture will cover them or painting is not complete.

Plumbers leave the job before the electricians start usually. Cut the vent pipe in two locations one 8" above the other and start 4 " below fixture height. Use ABS black glue - glue on a 45 deg plmg connector to each pointing back into the wall. Glue two 45 deg connectors onto the scrap of abs you removed after shortining it due to offsets. Take the leftover piece of vent and cut it in half. Now glue those into the saddle and glue the saddle back onto the vent. I wouldn't do this myself, but hey you asked what would work and I love to give sound answers to such riddles.:)

macmikeman, that might start a war with the plumber if he finds out someone is tampering with his installation. I'd hate to think that some of my wires got cut in the wall for retaliation Plus that still don't help me on remodel work.. Thanks anyway...Steve..

Spark, there was a huge amount of fooling around in all that nonsence I posted, I have never done anything even remotely close to that, but it sounded fun. Now for remodel work (by the way this is no messing around....) first I drill a tiny hole in the wall with my ever present 3/16 " tapcon bit (any bit would work, but I have that one in the pencil holder at at all times so it is handy.) and then I probe the wall with a piece of #14 solid to check for that there vent pipe first. If one is present in the way, I dap over the little bitty hole, and install two light fixtures instead of one or go the adjustable fixture housing method posted above.

Use the circular fan-rated boxes made by Arlington...

Wedge his pipe off slightly to the side and get to work. These boxes are easier than pancakes -- with more space.