Easiest way to enlarge an electrical knockout?

You might find a set of used KO punches on Ebay for a decent price. I knew a guy years ago who used a hole saw. Metal shavings weren't a problem for his work. It wasn't a super neat job either. The saw would wander a bit if I recall correctly.

Use a Sharpie marker to mark the diameter of your 3/4" hole around your

Harbor Freight also sells step drill bits.

TDD

Find an old radio hobbyist or an electrician with a chassis punch and buy him a beer.

If you are near a big city I think it is real likely you can rent them.

Oren,

I have a Fahrenheat FUH54 space heater, not a water heater. I have full access to both sides of the opening.

I just wonder how well a punch will work only having an extra 1/8" on each side of the existing opening.

Anthony

If you have a good rental place it should have KO punches.

Change the wiring method to something with a 1/2" connector?

will the box be overfilled? might be easier and more code compliant to just replace the box

Yes, the easiest way is a knockout punch. You, however, seem to be looking for the cheapest way. That would be a round file.

YEP, this is exactly what to do.

The cover on the water heater enclosure is removeable. At least on any I've worked on.. And I was not under the impression this was a water heater, but I may have missed it.

just replace the box

Except that from what is described, there is no box to replace. The NO is on a *heater* he's trying to connect. I suspect he has a *cord* that's too big. An option might be to install a box and transition from the cord to 1/2" liquidtight, etc that will fit.

Good point and now that I think of it the answer by "Caulking-Gunn" might actually be the best...to simply use a transitional fitting.

Half inch hole, 3/4" conduit such things exist and would make it a "no-mod" job.

You might find a rental place that has knockout punches.

Harbor Freight has step drills for relatively cheap. I doubt they're any *good* but as long as they make one hole, it's probably the easiest way to go.

I doubt they're any *good* but as long as they make one hole, it's probably the easiest way to go.

Years ago, when I did heating. HF has a three pack of step drills up to 3/4, but that's not big enough. Need one which goes to 7/8, and the knock out size is 13/16.

Two pack:

Either of these two should make 13/16 hole.

John,

After considering multiple options, I remembered I had a metal nibbler in my tool chest. I wasn't sure if it would handle the sheet metal on the heater, but it worked fine.

You can see the full process with pictures at:

Thanks everyone!

Anthony Watson Mountain Software

One thing obvious from a couple of your pictures:

You have too many clamps.

Wait...that's not possible! ;-)

You didn't show a picture of the side of the heater where the old hole was and how you filled that hole in!!

I used a standard knockout seal like these:

You can also see the back side of the seal on the right side of the picture in the "Rewiring the new cord" section of my web page:

Anthony Watson