Panel knockouts, make my own?


Old 01-11-06, 04:04 PM
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Panel knockouts, make my own?

I have a new 200 Amp panel that a 1" EMT flex conduit attaches at the top knockout opening. The opening could be made larger. I now need to add a 1.25" flex EMT conduit to the top of the panel but the only knockouts left are 3/4". Is it safe to enlargen one of the 3/4" opening to fit the 1.25" EMT flex or should I try to move the 1" (hate to lose that one) to one of 3/4" and enlarge it to 1" and then knock out the rest of the 1" knockout to fit the 1.25"?
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Old 01-12-06, 03:18 AM
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Is the panel hot? We use a knockout tool to do what you are talking about when a larger conduit is necessary in a panel. You don't want to drill in a hot panel, because of the flying metal. The knockout tools use two opposing discs with cutting edges and you tighten up on with a wrench until it pops out.
Old 01-12-06, 05:12 AM
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Here's a catalog of punch sets. You can often find them on online auctions and they are available at Graybar:

You can also drill it if you dare, but as previously mentioned, not with the panel energized. The punch sets are relatively expensive but much safer.
Old 01-12-06, 08:54 AM
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A punch set is far more expensive than you will want to spend for one project. See if you can rent one or have an electrician friend/relative to borrow one from.
Old 01-12-06, 04:15 PM
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You might also want to check with any sheet metal workers or air conditioning techs (older ones anyway who actually have sheet metal experience) you know to see if they have access to one of the punches that the others mentioned.

I had to do this same thing to my panel, and my father, a retired sheet metal worker, had a punch set I was able to use.

Failing access to a punch, you could probably do what you want with a bimetal hole saw. Drill a small pilot hole, and then use that hole to guide the hole saw. Get someone to hold a shop vac hose close to the drilling on the inside of the panel to collect the metal shavings.

The punch would certainly be MUCH cleaner.
Old 01-12-06, 06:07 PM
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Another thought is a step drill. They cut pretty fast and minimize chipping.
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