How much weight can an old work box hold?

Question

I will be installing new light fixtures in two bathrooms that look like this:

Each fixture will be replacing a light box. Meaning it is a simple chrome plated box about 30" wide with a plastic diffuser and sat on top of a mirror.

The challenge: The old light is connected to the power cable and there is no work box, it was simply screwed to the wall and wired up. The wire comes through the wall via a hole as big as the cable.

I plan on using an old work box to not only contain the cable, but attach the new light fixture to it.

My question is: How much weight can the old work box hold? (As it will be secured to the sheet rock and not a stud).

Answer 1

From what I could find, it doesn't look like these types of boxes are listed for any type of fixture support.

When looking at a box that attaches to a stud/joist using nails (B520P), it states.

Suitable for fixture support up to 50 lbs.

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With the the old work version(B618R), it states.

Not listed for fixture support in ceilings.

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A box like this (BH614R), states.

Listed for wall fixture support up to 10 lbs.

The last page of this catalog shows some round boxes, and the weight they are rated to hold.

Based on this information, I would say the box you want to use will support less than 10 lbs.

The best options in your situation, would be to move the fixture location to allow you to fasten the box to a structural member, or add a structural member to mount the box to.

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Update:

I contacted a company that manufactures these, and here is their response.

[Link to product omitted]

As shown on the link above this item is not listed for fixture support. We do have several other boxes that are rated for fixture support.

[Link to other product omitted]

^{The link for boxes rated for fixture support, pointed to boxes that attached to structural members.}

Answer 2

The ears on an old-work box (or the molly-like metal flanges on some) are pretty small contact points behind 1/2" drywall (or even 5/8"). It might be strong enough, but you don't want a lighting fixture with glass shades tumbling on Junior, Rover or Grandma.

What about cutting the hole for the box, inserting a piece of furring or lattice, about twelve inches long horizontally along the top of the hole the box will go in. You can hold it with a string tied around the middle as you position it. Then screw through the face of the drywall to cinch the brace to the wall. Dothe same on the bottomof the hole.

Now you can mount the box using screws into the new bracing. Touch up the screw holes with taping compound or spackle and a bit of paint.

P.S. This is still not a strong structural support, but should be able to hold a moderate weight sconce. I can't give you a real weight limit. For a seriously heavy unit, you should have a real brace tied into the studs.

Answer 3

My name is RatTent, I’m a certified electrician in the state of Washington. Those cut ins are rated for 6lbs we use them mainly for pendants and vanity’s. Nothing’s stopping you from using them in a wall(as show in picture). The information is on the cardboard that these cut ins come in.

Next time I think about it I’ll take a picture of the box and upload it.

Picture:

Answer 4

You can use an old work fan brace box. If you know the direction of your joists, you may not even have to get up in the attic.

Just cut a hole the size of the box, slide it in endwise, and twist the bar to expand it to fit snugly between the joists.