Every time I encounter one of those concentric ring knock outs on a panel or a large box, I end up butchering it. This is especially true if I’m trying to use the larger knockouts, like 1″ or 1 1/4″. I almost always end up bending the next larger ring as well.
Any advice on technique? Today I am going to try grinding the little attachment tabs on the appropriate ring with a dremel so that only the right ring will break out. Any better ideas?
Thanks,
cf
Replies
Greenlee, among others, makes knockout punches. Greenlee, in particular, is not cheap, but I picked up a set at an auction for a reasonable amount. The knockout punches are available in hydraulic as well as manual:
http://www.greenlee.textron.com/products/holemaking.html
http://www.protoolsdirect.com/mfg_dept.asp?dept_id=810&mf_id=42
http://www.e-sci.com/jensen/1/26/155/3073.html
Edited 3/22/2002 2:07:58 PM ET by CaseyR
Concentric knockouts are really not such a great idea. With punches and a plain steel box, you can put whatever hole you want wherever you want it. With concentric knockouts, if you run conduit to any but the largest hole, code requires you to use the special nut with the ground screw and a jumper on the inside of the box. Apparently grounding from ring to ring thru the concentric KO's isn't good enough.
-- J.S.
I don't pop out knockouts very often, but when I do I give it a sharp blow 90-degrees out from the attachment points. Meaning, halfway between the two attachment points, or 90-degress around the circumference from one of the attachment points. Usually, I place the tip of a screwdriver (all-pupose tool<g>) against the knockout and give the screwdriver handle a whack with the palm of my hand. This usually bends the knockout out of plane enough to grab it with pliers and bend it back-and-forth-and-back-and-forth until it lets go.
For any wondering I had to go with a new handle. 4Lorn was "taken" . I looked up my old user and password and tried it 3 times. No joy. System glitch I think. Hmmm.
On the topic. How to take a KO out w/o damaging the larger ones.
A large beater screwdriver used as a chisel and then prybar and following up with linemen's pliers. The pliers, Kleins (an electricians hammer), are used to pound the screwdriver at an angle attacking the metal at the point that one KO is joined with another. A half dozen quick, sharp blows cuts the tab and allows a whack with the Kleins , or a pry with the driver, to pivot all the smaller KOs for a quick grab and twist with the pliers. With a little luck a KO stack can be removed without greatly altering the ones to remain in about 10 seconds.
Smaller KOs are often upended for the easy grab with a forcefull jab of a beater driver or Kleins. Depends on which tool is at hand.
If you damage the larger concentric KOs placing a set of large OD reducing washers with the proper ID on either side of the box will reinforce the connection to the conduit. In cases where the conduit will likely be strained I frequently add a set of these reducing washers even if the remaining KOs are still well attached.
Better quality panel and boxes usually have the more durable, and ironically sometimes easier, KOs to work with. Some cheaper boxes are pressed to look like KOs but are not sheared through the sheetmetal . You can sometimes beat these to the point of caving in the side of the panel without poping the KO.
Thanks guys -
Too bad about your handle 4lorn(1). I had to re-register too (did all of us?) But no one is likely to take mine.
My boxes are of the "beat them to the point of caving in the side of the panel" variety. It's a 8x8x4 junction box from the orange box (where else), I forget the manufacturer. The 1/2 and 3/4 knockouts work fine, but the 1" and 1 1/4" knockouts are attached too well. FYI - a dremel makes all of the difference, but it takes a little time.
To add insult to injury, the KO's are also just a little too big, so the fittings kind of squeeze through. I'll pick up washers next time I'm out to neaten things up.
Can someone tell me the technical name of the parts I am supposed to use to "jump" the ground across the concentric knockouts? I'll pick those up when I'm out as well.
Thanks again,
cf
I think the item you are looking for is called a "grounding bushing" but since I don't work for Home Depot, I can't say for sure.
Knock out the smallest knock out first and work upwards. On some a/c heating units I had to install the supposed knock-outs were so stubborn, I just used my punch set. This gets expensive which is why electricians charge so much [tools]. A complete set for half inch costs about $30. For 3/4" and larger you need a special drive bolt with bearing [about $20 plus a punch and die which are about $20. Each. And that's for one size and the larger sizes cost more. The drive bolt [3/4"] requires a 3/4" hole which you can do with the 1/2" punch or a UniBit [step-drill] [$40].
Hole saws are a cheaper option but you need the bi-metal kind plus mandrel.
-Peter