Hmmmm... Maybe something like JB Weld to fill in the crack and perhaps prevent it from expanding when inserting the screws? If you get some JB Weld into the tunnel, you might have to tap it out back to the correct threads. Don't switch to something like self-tapping screws, sheetrock screws, etc. as the code says you have to use the machine screws that came with it.

I believe JB Weld is designed for repairing metal not plastic, but there should be an equivalent product that will work for filling plastic.

If you filled in the entire screw area with plastic epoxy by squirting it into the hole you should be able to fill the hole and stabilize the crack. You could also add some epoxy across the top on the outside of the crack.

Then use a drill and tap to rethread the hole. With a plastic box you might be able to just drill a hole a little smaller than the screw and let the machine screw cut the new threads.

You can also use a longer machine screw that would extend a little farther back than the existing crack, and get it to grab a more solid part of the threads in the box.

Bruce

Thank you for the ideas. I have already tried the longer screws and that just forced the split farther back. (The reason for this as far as I can tell is we have commercial/hospital grade sockets so plugging in and pulling out is very tight and puts stress on the structure.) Now the split is effectively the whole tunnel. I'll try a plastic epoxy sort of remedy, next.

if the tile is not covering any part of the box you can take a hack saw blade and slide it along the stud side of the box and cut the nails, remove the box and replace it with a cut in box.
It's not as bad as it seems and only takes a few minutes to cut the nails.

The link is to a device purported to repair the problem described. I have not personally used these.
I did not check the price but tooling to make these is expensive and the price no doubt includes amortization of that tooling over relatively small production volumes.
Other potential solutions may be found by Google search of " broken electrical box."

Here is a link that might be useful: Clip

bus driver - fantastic! I did try a fix today (before I logged in and saw your post), but if it does not work, then I'll be pursuing these G clips which are really a bargain considering the tedious fix they help one avoid. Here is a picture of what I tried today, removed the old screw tunnel with a chisel and cut one of the same off a loose, extra box including "wings" then used goop to glue it into position. I'll let it cure a full 3 days before re-assembly. I will be adding a patch plate behind the tunnel to finish closing the box back up, BTW. After examination, the problem was only with the bottom tunnel, so the top tunnel is intact and holds the anchor properly. Access into the box is tight as it's through the tiled wall which in turn is tiled over a former formica back splash that had a slightly smaller hole than the box edge

This post was edited by beautybutdebtfree on Mon, Feb 17, 14 at 22:43

Your "Fix" has eliminated the possibility of using the clip as the portion of the box for the clip has now been cut away. One of the causes of broken screw bosses is the use of wrong screws. Drywall screws are often used with disastrous results. The bosses are designed for 6-32 screws.
If the "Fix" is not successful, the only remaining alternative is box replacement.

Slap some epoxy in it. Then drill the holes out a little smaller than the screws. You dont need to tap the holes. The thread should cut thru the epoxy. I know that code says use machine screws like that ones that came with the receptacle, but I still use sheet metal or woods screws when a hole strips out in a plastic box. All it does is hold the receptacle in the box. There is no grounding issue. The box is PLASTIC.

you've completely ruined the box and voided the fire rating on it.
Electrical boxes have a 2 hour fire rating, yes even the plastic ones. Will this ever be a problem? Probably not, but there's no way that would fly if an inspector saw what you did.
From your picture it looks like the tile was done to the outside edge of the box like it should be. From what I can see you should be able to remove the box without much issue after cutting the nails. Why haven't you replaced the box instead of trying to cob and piece and part it together? It would have literally taken 5 minutes and you'd be done.

This post was edited by hexus on Tue, Feb 18, 14 at 8:57

Some have missed the point. The plastic is not threaded. The 6-32 screw cuts its' own threads in the hole provided. Use of other screws may put pressures on the plastic that are beyond the ability of that particular material to withstand without rupturing. And I think caused the initial and continuing problem in this instance.
Sure, there are plastics that are more pliable-- but they are not necessarily rigid enough or have enough fire resistance for this application.
By all means, I would use a tap and cut proper threads for any epoxy repairs.
I work on antique tractors as a hobby. Always when confronting broken parts, the various choices for repair are considered in light of which repair will ruin the part if unsuccessful. The least destructive is my first choice. The one that offers no additional options is always the last thing I would try.
In this case, the choice was skip Plan A, B and C and to go to the most extreme option first, Plan F.

This post was edited by bus_driver on Wed, Feb 19, 14 at 15:09

I did try 3 inch 6-32s as the first line of solution, however they did not hold. Now I know why. The bottom tunnel is ruptured, that is obviously why. It was less obvious why the top tunnel would take a screw for a while and then start slipping. The pictures show the actual construct of the box. The tunnel is OPEN with no enclosed surface for threading. Instead, a small metal insert at the tunnel opening has a tab that holds the screw thread. In the case of the lower tunnel, this was blown open and the whole assembly was gone. In the case of the upper tunnel, the tab was damaged although the tunnel looked intact.

The patch is working great, but I did order the G clips for the upper tunnel and any other box where I run across this.

For those of you who READ my post, it said that the box is inaccessable not due to the TILE, but due to the layer of formica, where the hole is smaller than the box opening.

I won't argue with the fire rating breach, and had I known of the G clips first I would not have hacked my box. I can only imagine the fire rating is for fire crossing the wall surface through the box opening from one side of the plane to the other, and in this case it now has a layer of tile to cross, so I am not losing sleep over this.

This post was edited by beautybutdebtfree on Wed, Feb 19, 14 at 21:27

Here's the other view, showing the open "tunnel"

"For those of you who READ my post, it said that the box is inaccessable not due to the TILE, but due to the layer of formica, where the hole is smaller than the box opening"

I read your post, obviously you ignored mine. How is the under layer of formica even an issue? Cutting it to the correct size would have been very easy. You obviously posses the means to cut things since you were able to hack up an electrical box just fine. Sorry if my solution didn't meet your approval. I'm not in the business to give jerry rig hack job advice.
You asked a question and were given legitimate fixes. Instead you took it upon yourself to not listen and do a hack job "fix" voiding listings. Why even ask for advice if you aren't going to listen? You're even trying to justify voiding the fire rating. Whatever helps you sleep at night.
Having something "work", and doing it correctly are two completely different things. Why not just epoxy the receptacle to the wall and call it a day?
As an electrical contractor things like this drive me up the wall. I can't stand it when people think they know everything and just hack job something together so it "works" and then try to defend it like they did it correctly.

The G clips arrived today and what a slick solution. Took me all of five minutes, and that was with difficult access and a fragmented tunnel. Once I got up in there I saw that the upper tunnel was ruptured as well around the screw hole.

It was a matter of pulling down the box edge and fragment edge and easing the spring clip with its "fangs" back onto the box, and seating it, centered. Then replacement of the recepticle via its 6-32 screws up and down, and the plate.

Well worth the purchase, the fix is rock solid with my plugs, and these are TIGHT sockets as they are hospital grade. I bought extra clips as I'm sure I will run across this problem again.

The clip vendor was very responsive and offered any help I needed, although it was pretty straightforward and idiot proof for the most part!

Below you can see the problem, the ruptured tunnel. Next post will show the G-clip installed.

And here it is installed, it will pull down into alignment as the screw goes in.

One more picture, showing the spacers used for the new tile thickness (neon yellow thing), the repair via G-clip behind the spacers on the box edge, and the box contents now back, installed.

This post was edited by beautybutdebtfree on Thu, Feb 20, 14 at 16:22

And I forgot the obvious: here is the G-clip product. It appears to be a tempered spring steel.

A special thank you to bus_driver for helping me become aware of this product.

This post was edited by beautybutdebtfree on Thu, Feb 20, 14 at 16:31

My assumption was that the clip required significant force to install and the portion held with the glue would break away in the process of installing the clip. But I have never used them.

Since the clip is apparently tempered (hardened) spring steel, the force to just push it on is pretty high, unless you pry open the "snake mouth" first, which is what I did using a medium large slotted screwdriver, twisting it to open one side. Once you get at least one "fang" of the "snake mouth" onto the edge of the box, then you just push it on with a finger, and then open the other side of the "snake mouth" with a slotted screwdriver and push that "fang" onto the other side. The strength comes from the spring steel "fangs" - once you seat the clip all the way back, it "bites" and is very stable. The "fangs" are angled so pushing it ON is no big deal once you are over the edge, but you could never pull it back OFF due to their bite angle, without opening the clip and unseating the "fang" point.

And on my glue job, the other part of that box will break before my glue job will break. It is very strong stuff. I didn't put a clip over my glue job as it is fine as is. I used the clip over the upper tunnel which I discovered was cracked also.

And looking at the physics of the G-clip: while my glued on transplant tunnel works fine, it doesn't solve the original problem of a weak plastic tunnel, and only a metal tab holding the 6-32 screw thread. In the original box, the metal tab makes contact with say 60 degrees of 360 degrees of thread around the screw, so if you lose any or much of that tab, you have lost anchoring ability.

The G-clip uses a machined hole for the 6-32 screw, and its thread contact is about 300 degrees of the 360 degrees of thread, much more robust. Furthermore, if there ever WERE a breach of thread, it's a matter of slipping a flat screwdriver up under the fangs, removing that clip, and replacing it with a new clip, also a five minute job.

I do appreciate a good solution!

This post was edited by beautybutdebtfree on Fri, Feb 21, 14 at 8:02