Outlet Boxes: clamps & gromets required?

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I'm adding a couple of steel outlet boxes and switch boxes in my residence, fed by 12-2 w/g Romex. I've noticed in Lowes some of the boxes have clamps built inside to secure the Romex, and some don't. Are clamps required by NEC?
The other thing I'm wondering about is the knockout holes on the sides and back of the boxes. Are rubber grommets required for the holes I run the Romex through?
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Whether they are required or not, I always use the clamps if they come with the box. Otherwise I use rubber grommets. Metal rubbing on plastic usually winds up with the metal winning and with electricity, the results are often not pretty.
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On Thu, 29 Jul 2010 14:00:19 -0500, "The Post Quartermaster"

grommets used in interior domestic wiring.
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I havn't got the electrical code handy, but that's my thought. Sharp edges of metal boxes aren't good for wires.
When I replaced my old furnace, I found out that the last guy hadn't used a romex clamp where the wire comes into my furnace. I'm surprised and pleased that the metal edge of the furnace hadn't worn through.
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Clamps are required. The knockout holes require separate clamps. The reason those holes are used is to allow connection of conduit as well as Romex and BX type cables. (you simply use a different clamp/ connector for each type of wiring.) If you buy boxes with integral clamps make sure you get the ones for Romex not BX (they look similar but are subtly different.)
For Romex, you can also use the little black Arlington buttons instead of clamps
Romex clamp:
http://www.acehardwareoutlet.com/productdetails.aspx?sku=998017976
Arlington button:
http://www.aifittings.com/whnew104.htm
nate
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http://www.acehardwareoutlet.com/productdetails.aspx?sku 8017976

Thanks. The Arlington buttons look pretty nifty, serving as both a grommet and clamp. Can they be split and added to existing steel boxes too.....without pulling the Romex back out and gaining access to the back or side of the outlet box?
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No. They're supposed to be pushed through the hole from the outside, and I don't see how you would accomplish that without pulling out the Romex, split or no. There's a flap inside the button similar to the ones used on plastic old work boxes, to grab the cable - trying to push the cable through the button in the reverse direction from what is intended seems doomed to failure.
I don't think you need to worry about having a "grommet" as a properly installed cable clamp will not allow the cable to move relative to the box at all, so no possibility of chafing exists. The Arlington button and the traditional Romex clamp accomplish the same thing but in different ways. The main advantage of the Arlington button is reduced installation time.
nate
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*Depending on the manufacturer, some button type Romex connectors come from the factory with a slit in them. I have installed a few of these after the wire was installed. I used Channellocks to squeeze the button over itself a little and pushed it into the hole at the same time while also trying not to damage the cable. A third hand could be useful, but not required. One trick I learned in the process is to install the button over the individual conductors and not the outer sheath. Once the button is in place you can pull the cable with the outer sheath through.
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N8N wrote:

Thanks for the info. What about the little plastic (often blue in color) outlet boxes? They have rectangular knockouts on the back end; is there a clamping fixture for them, or does the wire just hang freely?
Jon
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better word), as they close back against the cable and hold it. I absolutely hate plastic boxes.
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wrote in message

that get completely knocked out.
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The Post Quartermaster wrote:

Aye, I absolutely hate them as well, but they are (to my knowledge) the only ones available with the flip-out "wings" to install them into a pre-existing wall (without cutting out a hole larger than the box itself).
Jon
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don't require opening the wall larger than the box. I'm kind of partial to the old fashioned "madison bars", but clip on wings and other stuff are also available.

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RBM wrote:

Ah, cool, it helps to know what those things are called. I'll try and see if I can acquire some locally for the 240 box I'm putting in for my welder.
Jon
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On Thu, 29 Jul 2010 16:31:18 -0700, "Jon Danniken"

the front, through the hole, with expanding "jaws" to hold to the drywall
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Felix, the trouble with Lectricians is them bastards want to be PAID. What's up with that?
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snipped-for-privacy@snyder.on.ca wrote:

I don't see stuff like that at my local hardware store. Professionals get all the good stuff.
Jon
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On Thu, 29 Jul 2010 20:14:11 -0700, "Jon Danniken"

I bet they do. Lowes and the BORG certainly do. Perhaps you don't know what you're looking at? BTW, they're normally called "old work boxes".
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snipped-for-privacy@att.bizzzzzzzzzzzz wrote:

Well, I've seen the plastic boxes with the wings that flip out and tighten up against the back of the drywall, and I do know the difference between old-work and new-work. Just haven't seen any metal boxes with a similar feature.
Jon
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wrote:

Boxes made for existing walls will have some sort of bracket to prevent the box from falling into the wall, then you need some other type of device to prevent the box from falling out of the wall, such as plaster tins=madison bars=switch box supports. But be careful as things are "normally" called by different names in different places. Such as cut in gem box = wet wall box =old work box

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