Romex/ceiling lights/ no boxes - how to hit knockout dead nuts

[Shovelhead]

New installation of 4' LED surface mount fixtures. Ceiling will be 3/8" Beadboard panels.
Fixture housings are just under 4" wide and the placement of the lights lands the 1/2" knockout between 2x12 ceiling joists. There's a floor/loft above.

So I'll have two tail's of romex entering the fixtures. I ain't the fellers putting up the ceiling but is there a trick to positioning the romex so they can get the exact measurement for cutting a hole in the ceiling material to line up dead nutts with the knockout location?

Only thing I can see to do is poke a larger hole and measure that beadboard panel twice, and then measure it again 10 times. ??

Thanks

 

[rlitman]

Exact? I'd use my 3-plane laser to plumb from the ceiling location to make a mark on some tape on the floor. Protect that floor mark, and when the beadboard is up, you can use it to plumb back up to the ceiling.

 

[Innovate1]

Not sure I follow the layout completely but you could put a 2x between joists with a hole that the romex goes through. That seems like the best way to make sure they end up where you need them.

 

[sparky 1971]

The ceiling guys will find a way to screw it up. Throw a scrap chunk of 2X4 up and nail a single gang box to it.

 

[Zeke]

I'd do as @sparky 1971 1971 says and at least push the wires though some 2 x 4 blocking. It's not moving then. If they can't mark the hole where the NM-B comes down, then they shouldn't be doing the ceiling.

Okay, I know it's tough to hit every hole on a large job w/o one miss. If I was doing this for myself, I'd put a nail or something to make a witness mark when the panel is dry fitted. Then drill a pilot hole from the back. If they have to double check, then that's what they do.

I assume they will be on a rolling stage and can make all the holes while up there. Staple the cable so that it can be pushed back up the hole and pulled down when the panel goes up. Your witness marker can be used at each hole if you make something up that will fasten to the hole and then take out as they go. 2 light fixtures in one panel, 2 locators.

 

[sparky 1971]

I'd do as @sparky 1971 1971 says and at least push the wires though some 2 x 4 blocking. It's not moving then. If they can't mark the hole where the NM-B comes down, then they shouldn't be doing the ceiling.

Okay, I know it's tough to hit every hole on a large job w/o one miss. If I was doing this for myself, I'd put a nail or something to make a witness mark when the panel is dry fitted. Then drill a pilot hole from the back. If they have to double check, then that's what they do.

I assume they will be on a rolling stage and can make all the holes while up there. Staple the cable so that it can be pushed back up the hole and pulled down when the panel goes up. Your witness marker can be used at each hole if you make something up that will fasten to the hole and then take out as they go. 2 light fixtures in one panel, 2 locators.

That can be done as long as the hole in the blocking is large enough for the clamp, connector, or busing that is coming out of the back of the fixture is big enough. Then when the ceiling panels are installed, the installers have to make the hole big enough. When they don't, someone is going to be screwing around chipping ceiling out until the hole is big enough for whatever sleeve is being used to recess back. One fixture winds up being 1/4" off to the East, the next is 1/4" off to the West and the two are 1/2" off from each other. It might not be noticeable, but it could very well be.

If single gang boxes are used, the installer can use the entire 1-3/4" X 3-1/2" area of the box to play with and get everything lined up close to perfect. I'd probably lay everything out on the floor and snap chalk lines down there, then use my laser plumb bob to transfer everything to the ceiling where the lights will be. If the ceiling is painted white with semi gloss, it would be even better to snap the lines on the ceiling then wipe off the visible chalk after the lights are up.

 

[mm08822]

Exact? I'd use my 3-plane laser to plumb from the ceiling location to make a mark on some tape on the floor. Protect that floor mark, and when the beadboard is up, you can use it to plumb back up to the ceiling.

Laser is the best way once the centerlines are locked in.

• I would do this by laying out the fixtures on the floor to the same centerlines they will be on in the ceiling.
• Find the knockout(s) in the fixture and that becomes the point to mark on the floor. (or measure and record that point off of the walls)
• Use the laser to transfer that point up into the ceiling.
• Run the romex in the ceiling, bore holes, staple neatly but leave plenty of slack in each cable at each knockout location(s).
• Coil the slack of the cables horizontally so they are loose but above the joist plane AND at the knockout location.
• You could even attach 3-4' of mason's line to the cables so there is more to snag with a snake later.
• After ceiling is up, you transfer the floor points onto the ceiling with laser and drill 1"+ hole in ceiling material.
• Use a piece of wire, coat hanger or snake to grab the string and pull it thru each hole.
• Pull the string until the cable ends come thru the hole.
• Use the laser to string the lights so they are straight, stay on the centerlines and don't fish-tail.

 

[Shovelhead]

Thanks for the ideas.
I thought about the single gang box but good God I done got blocking/nailers screwed up there for all 7 fixtures to have some meat behind that ceiling material. Overkill and likely not needed for these lightweight fixtures, but, I did it anyway.

was hoping to avoid my old wore out *** going up and down that 8’ stepladder a jillion more times measuring, cutting blocks, mounting the blocks and mounting boxes. But that would probably be my best bet.

I will get my carpenter over there to take a look before I do anything I think.
He may have something that makes it best for him. I’m guessing he’s dealt with this before.

Another thing is the center of my fixtures on one side is 4’ off the wall. The ceiling is 4x8 sheets. May make those 3 easier because he could notch the edges of the sheets. The fixtures lay across the joists, not inline with them.

 

[Shovelhead]

Laser is the best way once the centerlines are locked in.

• I would do this by laying out the fixtures on the floor to the same centerlines they will be on in the ceiling.
• Find the knockout(s) in the fixture and that becomes the point to mark on the floor. (or measure and record that point off of the walls)
• Use the laser to transfer that point up into the ceiling.
• Run the romex in the ceiling, bore holes, staple neatly but leave plenty of slack in each cable at each knockout location(s).
• Coil the slack of the cables horizontally so they are loose but above the joist plane AND at the knockout location.
• You could even attach 3-4' of mason's line to the cables so there is more to snag with a snake later.
• After ceiling is up, you transfer the floor points onto the ceiling with laser and drill 1"+ hole in ceiling material.
• Use a piece of wire, coat hanger or snake to grab the string and pull it thru each hole.
• Pull the string until the cable ends come thru the hole.
• Use the laser to string the lights so they are straight, stay on the centerlines and don't fish-tail.

Sounds wonderful. But.
I don’t own a laser and it would take me a month to figger out how to use the damn thing.
I‘d be way better with a tape measure and a good eye.
Just a dumb country boy.
Part hippie part redneck, always a suspect.

 

[sparky 1971]

Or...nail a box to the ceiling on the joist closest to the center of the fixture. Then when it's time to put the fixture up, drill a 7/8" hole in the back of the fixture wherever center of the box winds up. Then install a snap in bushing in that hole and pull the wire into the fixture and be done with it. That's probably the fastest overall method in total time of rough and finish.

Depending on which direction the fixtures are going to run, the box might need turned 90° and obviously, won't nail on to what's there. There are screw on single gangs meant for horizontal wall installation (Arlington F101H), but the only way I've ever been able to get my hands on them is to order them. Southwire also makes one that is available at some box stores, but I don't like them. They do work in a pinch though.

Arlington | F101H Product Information

One Box Non-Metallic outlet boxes. Single Gang. Horizontal. 22.3 cu. in.

www.aifittings.com

https://www.menards.com/main/electrical/electrical-boxes-covers/electrical-boxes/southwire-smartbox-trade-1-gang-22-5-cu-in-horizontal-electrical-switch-outlet-box/msbhz/p-7720120058392483-c-6425.htm?tid=-4697013053989519034&ipos=19

One could also use a 4" square box with a bracket and a mud ring turned the right direction.

https://www.menards.com/main/electrical/electrical-boxes-covers/electrical-boxes/raco-4-galvanized-steel-square-junction-box-with-bracket/8196/p-1444451760890-c-6425.htm?tid=3530417942528034208&ipos=28

 

[Jim greengo]

Uni bit!

 

[rlitman]

...

• You could even attach 3-4' of mason's line to the cables so there is more to snag with a snake later.
• ...
• Use a piece of wire, coat hanger or snake to grab the string and pull it thru each hole.

Instead of string, if you have a ball chain or some magnetic sash chain, use that. Then you can use a magnet to bring it to the hole.

 

[alfredeneuman]

I don’t own a laser and it would take me a month to figger out how to use the damn thing.

Before lasers we used plumb bobs.

 

[Shiftless]

Before lasers we used plumb bobs.

And plumb bobs never come out of storage with dead batteries and you can use them easily in bright sunlight.

(I have a laser level and at least 2 plumb bobs in a drawer somewhere)