An electrical contractor told me about plastic 4" round ceiling boxes. He said that in order to be rated for 50 lbs. you had to install a screw in the box and attach it to the ceiling joist. I asked him, OK where does it say that? and he said he the last AHJ told him.
Now I don't know if it was true or not, and I was trying to find something on either Slater or Carlon website, but all I found is that those boxes are rated for 50lbs. I tried to find installation instructions, but nothing was written there either. Anyone heard this before?
It's been awhile, but this sounds somewhat familiar... Some Boxes are supposed to be for Fans, but say the Fan has to be supported indepentantly of the Outlet Box (screw through Box). Maybe that's what he means?
I found the following for one Brand:
Weight Limits: Fans and fixtures are supported independent of outlet box. Mounting screws go through box and into joist. Box will support up to 70 lbs. for fans and 90 lbs. for fixtures.
This sounds a bit misleading, as the box isn't actually supporting anything if the mounting screws go into the joist.
The TP 1300 or equal by other mfg does allow the fan support hardware to be attached direct to framing. The TP 16511 type is a nail-on & 35# rated, and I know of no provisions to 'attach' any type of fan braces to that box.
I'm quite sure that some enterprising person could mount a 2x? over the top of the box & run lags/screws into that but ...bye, bye listing.
The fan boxes I see are nailed/screwed to the side of the joist and the only real difference I see is the mounting screws are #10 and they extend through the ears to the back of the box. I may have one here somewhere. I see nothing in the white book that indicates any more support is required than what is provided by the supplied mounting bar or bracket.
You can't tell from the picture of this Box, but there is a heavy metal plate that goes behind the area that screws to the ceiling joist and across the top of the box to support the fan itself. These are not your average plastic fan boxes by a longshot.
You can see it by clicking on the 'New Release' picture under the Box on page below:
No to all the above. The box I saw was a black box that looked like Slater I think. The EC on the job told me that he failed in another town because he did not have the screw there. He said the OTHER AHJ told him that it had to be installed. He said something to the effect, "When there isn't a screw there the box is only rated for 30 lbs' , but when you have the screw, it is good for 50lbs."
Now I know this other AHJ and he is a nit picker. He likes fail guys for anything that he can. He usually does his homework and finds out small details with which to fail you. However I think that sometimes he will stretch a point just to be able to give you a red sticker.
So when this EC looked to me for some guidance, I told him that I would look into it. I have seen the boxes and they do have a small hole in the top where a screw could fit through and hit the rafter. I just can't seem to find more info on the matter.
This sounds like a question for the manufacturer. They are the ones who did all of the engineering to certify that their boxes are 50 lb rated. I looked at several pages and I did not see anything that indicated that you needed any more than the fasteners in the mounting bracket. The ones with the 2 captive nails seem to be 50lb rated.