stripped grounding screw hole

[PoorOwner]

almost finished up a weather proof box, all conduit and ears mounted. The last step include putting in the ground wire in one of the holes, the screw is supposed to self tap but it was just hard to turn and the hole has stripped

I put in a pan head steel screw from a plastic anchor but it is sheetmetal/wood threads not machine threads, it is holding a solid Cu Wire against the box interior just fine, I think better than that 10-32 self tap ever was going to be.

Just not sure if I should continue to mess with it with the tapping a bigger hole idea, I know NEC wants like 3 threads of engagement in a sheet metal box, not sure how they have it defined cast aluminum box with a grounding boss on it? The box don't have any threads machined in any of the holes.

The problem with tapping is that the tap don't start to cut threads until about 1/4" (the first little bit does not cut), I did try a 10-32 tap but didn't get very far because of the tap so didn't think drilling for 1/4-20 will be any better, but it may work with a thread restorer that starts to cut right at the end. I don't have the correct drill bit for 1/4-20 anyhow....

So bottom line is was using the non-machine screw OK here? The box itself is connected to EMT so the ground screw is probably not necessary but due to the raintight connector and gaskets etc I wanted to ground the box.

 

[alfredeneuman]

The NEC prohibits sheet metal screws to be used as ground screws (including TEK screws).

 

[sberry]

Sheet screws in sheet are not allowed and with good reason but in that box I wouldn't lose sleep with a good tight repair. In any of these I spray or drop of oil on a screw when I install.

 

[PoorOwner]

Thanks

I know the box is grounded in 2 ways and my house not going to burn down by this. Sometimes hard to go by NEC all the way... things like if I keep 6" of all wires I won't be able to close the box.

 

[rlitman]

...The problem with tapping is that the tap don't start to cut threads until about 1/4" (the first little bit does not cut)...

That's what a bottoming tap is for. You need one if you want to tap into a blind hole.

 

[PoorOwner]

That's what a bottoming tap is for. You need one if you want to tap into a blind hole.

Thanks. First time heard of that kind of tap.
Should do the trick.

 

[matt_i]

Be wary of the bottom tap as it doesn't self-align nearly as well as a tapered tap. So its hard to get started, by hand, in a hole without threads as the tap immediately following the pilot drill. It will do the job though. I have seen sliding tap guides for hand taps...

Drill press to hold the tap would be ideal but it sounds like the box is already mounted and wired...

 

[rlitman]

Be wary of the bottom tap as it doesn't self-align nearly as well as a tapered tap. So its hard to get started, by hand, in a hole without threads as the tap immediately following the pilot drill...

Correct. It isn't for starting the hole. You use your regular tap to start, then switch to the bottom tap once you have a few good turns in.

Also, if you ever break a tap, just grind the end flat, and you have a new bottoming tap.

 

[rtz]

Would like to see a picture of the box.

 

[PoorOwner]

ground point is at the bottom of the picture, center of the box

 

[sberry]

I fix them with a sheet metal screw like you were going to do. Make sure its tight and move on. As I said before, I spray all the screws that go in to these boxes.

 

[PoorOwner]

ok gotcha I think was going to move on with my fix, it is tight..

but I got a 13/64" drill bit and 1/4-20 tap.
If I attempt to tap a 1/4-20 do you think the threads will hold torque?

 

[tyme2par4]

ok gotcha I think was going to move on with my fix, it is tight..

but I got a 13/64" drill bit and 1/4-20 tap.
If I attempt to tap a 1/4-20 do you think the threads will hold torque?

Personally I would go with a 1/4-28. That will give you more threads in the thin metal.

 

[teamextreme]

I would just stick with what you have. Those pre-threaded holes in bell boxes are in crappy cast material that strip out easily and are usually threaded into a hub or stud that doesn't have a lot of material around it to drill out. The jump from 10-24 to 1/4 is pretty big and I doubt you'll have much material left for a solid thread.

 

[alfredeneuman]

Just drill a hole through the main body of the box and use a machine screw and nut.

 

[PoorOwner]

OK I think I am done dealing with this,
one more thing since I showed the picture of the box I have

what kind of cover is best for this?
They have a plastic one and a metal one, they both have a gasket.

metal
https://www.homedepot.com/p/HUBBELL-WIRING-2-Gang-Weatherproof-Gray-Blank-Cover-5175-0/204208003

plastic
https://www.homedepot.com/p/BELL-2-Gang-Blank-Plastic-Cover-Gray-PBC200GY/204125735

 

[rtz]

I always wondered if code called for one material or the other. Odd they offer both otherwise. But maybe more important if you buy 100 or 1,000 of those covers.

 

[PugetDude]

I've used a small piece of copper wire on stripped holes like that- just drop a 1" long piece of stranded wire in the hole, tighten the ground screw up snug and trim the excess.

 

[rburke65]

That is also a good fix with the stranded wire.

 

[PoorOwner]

I've used a small piece of copper wire on stripped holes like that- just drop a 1" long piece of stranded wire in the hole, tighten the ground screw up snug and trim the excess.

Have heard of using toothpick for wood material
That’s a good trick for soft metal.

 

[sberry]

I work on my own a lot, stuff I am going to own a long time. Nothingbtrashes an investment like corroded screws when needing to service something. I make covers for the top on a lot of outdoor and often spritze the inside of those boxes with spray before mounting the devices. It simply keeps humidity from attracting right off the bat. A little silicone across the top seal of a box and some sealer in vertical plugs don't hurt.
Water intrusion wrecks that stuff, promotes corrosion threaded screw or not. A lubed screw makes a little better thread, doesnt let the dross stick. Keeps it from sticking during installation.
We have hundreds or 1000's of bolts, i can tell when removing one been in service if the installer lubed it, even outdoor for decades,,,, sprayed comes apart. When they are tight and dry they are stuck.

 

[sberry]

Alum boxes, alum hole, copper wire and a steel screw. What could go wrong with that?

 

[PugetDude]

Alum boxes, alum hole, copper wire and a steel screw. What could go wrong with that?

The aluminum box comes with a tapped hole designed to accept a steel screw that holds down a copper ground wire.
Is there a point to your question?

 

[alfredeneuman]

The aluminum box comes with a tapped hole designed to accept a steel screw that holds down a copper ground wire.
Is there a point to your question?

Dissimilar metals?

 

[sberry]

And not all are tapped. I usually spray a drop onit, run it in fully, back out and install the wire.

 

[PugetDude]

Dissimilar metals?

Yep. From the factory... and approved by NEMA and the NEC.
Trying to figure out why sberry thinks it's a problem.

 

[Bert_]

It mainly just the weather in my opinion, steel rusts. Brass or stainless screws would be great but I usually put a dab of anti seize and drill a weep hole in the box.

Nothing worse than trying to change an outlet or something after 10 years and all the screws are rusted and break off. Happens with motor terminal boxes too, that's even worse since you talking about an expensive motor. I know of a few with the cover held on by duck tape.

 

[alfredeneuman]

Re: anti seize
NoAlox works great for that use as well.

 

[dscheidt]

Have heard of using toothpick for wood material
That’s a good trick for soft metal.

It also works for tapcons hat strip before they're tight, at least for low load stuff (like a 1900 box).

 

[PT Doc]

Or you could use a spiral flute tap and the chip will come out the same hole you entered.