I’d like to run the wire into the octagon box from the “top” (in the knock out with the pencil in it). However, the way the wire clamps on the inside are designed would suggest it is not ideal ie, does not secure it well and has a rather “sharper” edge. Having at knockout designed on the top would suggest this is acceptable. Am I missing something? Thanks! enter image description here enter image description here

Example of how the octagon will be mounted: enter image description here Thanks!

  • It's not clear what you're asking .The cable passes along the interior clamp at the side of the box, where the dimple in the retention plate makes contact with it. This strategy has been used for decades.
    – isherwood
    Oct 12 '20 at 21:08
  • Likely running the cable backwards (directly into the back of the box, not up the side).
    – Ecnerwal
    Oct 12 '20 at 21:11
  • Can you use a version of the box that doesn't have the built-in clamps? Oct 13 '20 at 1:17

To use the knock out in the middle of the box you Need to use a lock nut type clamp.

You remove the lock ring from the clamp and pass the threaded part of the body through the knockout from the outside and then place the lock nut on the threads from the inside of the box And tighten.

Then you can thread your NM Cable (Romex) through the clamp and tighten down the clamp screws.

enter image description here

This article will explain it.

  • Thanks Alaska Man. I’m familiar with the approach you mentioned, however, I cant use that middle knock out. This octagon will be screwed to a brace in the ceiling (mockup example in additional picture just added). This being the case, i was hoping to be able to go through one of the hole off center (the one i knocked out in the example) Oct 12 '20 at 22:04

Junk the box. Get one that does not have interior cable clamps, and simply has multiple 1/2" knockouts. Use the cable clamp recommended by Alaska Man.

That is not the right box for you, since it does not do what you want.

  • Yup, I’ll get a different one. No biggie. I just had a few of these ones and was wondering what the logic was for having those knockouts on top. (And not wanting to make a trip to get a new one, I’m out in the country!) Oct 13 '20 at 12:32

The knockout indicated on the top looks about the same as those on the sides -- same shape, same size, same distance to the corner, etc.

The clamp bar inside the box is held by a screw. Could you remove and re-install these so that the screw draws the clamp bar up against the side wall of the box, rather than against the top of the box as it is now? The pictures don't show the side wall of the box clearly so I can't see whether there's a hole already drilled for this in the side wall.

  • Yes, those knockouts on the top (except the center one) are the same size as the ones on the side. I tried re-installing the clamp bar flipped around but it doesn’t line up right to secure the wire. Oct 12 '20 at 22:09

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