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Can I use a hole saw to cut some new holes in the back of an outdoor breaker panel? Turns out the knockouts provided happen to be below the fire blocks in my walls... Anyway, with a small amount of luck and measuring, drilling new knockouts in the top might provide some access above the fire blocks.

Alternatively, I could always go back to my stellar idea about external conduit, but with THHN wire going in the conduit and many parallel conduits (like 6 per box to max out at 4 conductors per conduit). It'd be a whole heck of a lot easier than running the wire through the walls (I guess).

  • Could you flip the box top to bottom and use the existing knock-outs? I guess if you already have it mounted and supply wires in, that would be too much trouble. – Jim Stewart Mar 1 '17 at 13:23
  • @isherwood You are right and I just threw that in because it was late and I was frustrated by the situation. That one is also easier to just search on Google. – Hari Ganti Mar 1 '17 at 21:50
  • @JimStewart Nope. It's a NEMA 3R box so it must be oriented the correct way to retain its weather rating (also the wires bit). – Hari Ganti Mar 1 '17 at 21:51
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The answer is Yes you can add holes to the back of the box with a hole saw. Hole saws and slug busters are used by Electricians regularly for this. A 7/8" hole saw will provide the correct size for a 1/2" conduit, 1-1/8" will provide the correct size for 3/4" conduit and 1-3/8" is the size for 1" conduit. I use carbide cutters because they are a bit faster and last longer but a standard bi-metal hole saw will work with oil or cutting fluid if cut at a slow speed (full speed / no oil will will over heat the cutter and the teeth will dull quickly). Make sure to provide a little space from the wall of the box so the lock nut will fit inside the box. I usually cut my holes at the top or bottom sides so the wires look neat and installed in a workman manor that code requires.

  • Thanks @EdBeal, I can't actually go through the sides because the panel is surface mounted outdoors, but my plan was to cut four holes near the top at the back of the panel. Many smaller holes seems easier to manage than fewer larger holes. – Hari Ganti Mar 1 '17 at 19:29

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