I'm going to bid on a project where it is new construction and all the studs are metal. There are knockouts already in the studs but they are "kinda" rectangular but I cannot find any premade grommet to fit this strange looking hole.

If this is the wrong place to ask this question and if anyone has an URL to suggest a better place to ask I would appreciate passing that information on to me.

My question is two fold. First should I put in any grommet material to prevent cutting the cable when I pull it (assuming I can get the job). If I should be installing grommets on each stud, where should I be looking to find this material?

Mike Zemina

Greenlee makes a product for this situation. It will punch holes in the stud and you can then place a plastic gromet in that hole. You would be very wise not to run your wires through the existing holes in those studs. They can rip the insulation form your wires as you pull them through. Electrical supply has the tool. Describe what you want and they will understand.

Alan

Caddy also makes hangers that fit into the existing holes and keep wires from scraping, although the preferred method for running through these studs is to use flex. But that is not necessary by code for low voltage, so you are approaching this the right way. The Greenlee approach will probably be needed at some point, because framers do not always place the studs so the holes line up.

You definitely want to use grommets with anything that's not in conduit or flex/bx.

I agree with EBG that you will invariably face a wall where the carpenters (or are they called metalworkers at that point??) will use the scraps for areas under windows, stairways, knee walls, etc. and the nice little knockouts that the manufacturer puts in aren't at the right height, or are on the piece that was cut off and already used. Any electrical supplier and/or the building materials supplier that provided the metal studs should have the right grommets.

Greenlee makes a step bit for holes up to 1-3/8" (catalog #36414) so you can put your holes anywhere. It costs about $50, but is worth every penny.

After drilling you can use their bushings (#711 or #712) or any plastic snap-in grommet. Making your own holes is such a convenience after the electricians have filled every existing hole with BX. You can buy Greenlee stuff at Home Depot, if you can tolerate the store.

[Link: 198.247.193.8]

[Link: 198.247.193.8]

[Link: mcm.newark.com]


- Doug @ HomeWorks

Ernie,
Can you provide more info on the Caddy hangers?
Mike

Yeah - I saw that. It would be a pain to manually punch holes in over a hundred metal studs though. I was hoping someone would know of a manufacturer and place I could buy grommet for these wierd rectangular punchouts. But from the sound of it there may not be.

Thanks for the info.

Mike

Mike, the standard steel-stud snap-in grommets work just fine in the factory keyhole knockouts. Here are a few pictures of these grommets in place:


[Link: content.ll-0.com]
[Link: content.ll-0.com]

Good luck, I have done several jobs with metal studs, and they are a pain in the as*, I would suggest bumping up your labor rates and/or plan on a little more time on the job.

I do many commercial jobs, most of which have steel studs.

I think that steel studs are much easier to work with than wood. There are no fire-blocks and you usually don't have to drill. Simply snapping plastic grommets into the holes is usually all you have to do to have a big hole to run wires. If you need more holes, you can use a punch (about $200.00) that will puch a 1 3/4" hole in about 2 seconds. If you can't get your punch to fit in the place you want a hole, you can use a 1 3/4" hole saw and drill through in about 15 seconds. It is very easy. Compare that to drilling equivelent size holes through wood studs, top-plates, posts, fire-blocks, and joists. We can wire 20 data runs, 20 phone runs, 15 speakers, and an elaborate network of audio/video wiring in one day with two guys (and they aren't even working that fast). This is one reason that I like commercial better than residential.

The only bad thing is that you can cut your hand on the metal if you are not careful, so wear golves.

If you see metal studs, be glad.

Larry, Thanks for the pictures. Yes the keyhole punchout is what I am dealing with and am having a hard time finding grommets. Maybe I am asking the wrong distributors. Can you provide any details to the vendor and I can have the distributor order for me?

The keyhole I am dealing with looks like this:
[img] [\img]


Mike

This message was edited by mzemina on 10/11/04 10:43 ET.

Mzemina,

Remember that just because the hole is shaped like a keyhole, the grommet doesn't have to be. The rubber and plastic grommets are flexible! You just need to get a grommet with the correct circumference for the rectangular opening you have.

I suggest ignoring the small part of the keyhole, and only use the top rectangular portion from your drawing.

You can calculate the circumference of the rectangular opening using:
L = Length, W = Width
( 2 * L ) + (2 * W ) = Circumference

You can calculate the equivalent size round grommet to buy from:
C = Circumference, D = Diameter or Round Grommet, Pi = 3.1416
D = C / Pi
or
D = [ ( 2 * L ) + (2 * W ) ] / Pi

I've run wire in metal studs, and I also much prefer it. Really simple to pop out knockouts, and pop in grommets. The metal studs I used had some many knockouts available, that I never had to cut a hole!

Happy Pulling!

Went and did a quick google search and found this:
[Link: outwater.com]
You'd just have to cut to lenth for your hole. I'm sure other possibilities are out there.

This message was edited by bcf1963 on 10/11/04 12:22 ET.

No, BCF, those aren't approved for this kind of work.

Mike, go to any nearby electrical supply house (ask an electrician). This is a common item. Local home hardware stores might even carry them.

Why do you think that? They are Mil Std 21266. The standard covers flammability and abrasion resistance. These are actually manufactured for use in running wiring bundles through bulkheads and ribs in aircraft. You think running a wire bundle through a metal stud in a stationary house is a tougher application than an aircraft?

mzemina

Great timing, I'm in the same boat with an upcoming job.

Larry, Doug, Alan thanks for the ideas and the links