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I've come across this using "old-work" boxes, but all plastic boxes for switches and outlets are basically the same:

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These boxes have 4 knock outs per gang and they open at an angle. They seem to be made to allow the wire to enter one way and prevent it from slipping out like a basic clamp.

From time to time, one of the plastic tabs will break off leaving an open hole. I've also found installed boxes that have the tab missing.

So, is it OK to use the box with a broken tab? If not, to what level is it "not ok"? Is it a best practice, or is it to the level that an inspector would make you replace it?

  • Cables are typically required to be anchored (stapled or clamped) within 12" of the box. If that's done, it's probably not an issue. Fiber boxes often have knockout ports with no clamps anyway. – isherwood Dec 4 '15 at 19:14
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    On non-metallic single gang boxes 2 1/2 x 4, the cable does not need to be clamped if it is secured within 8 inches of the outside of the box (NEC 314.17(C) Exception). Therefor, on those, if the tab breaks off, no issue. On all others, since the tab is the clamp, it would seem to be a code violation. – bib Dec 4 '15 at 22:47
  • Do you mean is it okay to have a wire installed in a knock-out when the tab is broken, or just is it okay to have a knock-out missing a tab, but unused? (I think it would probably be good to answer this question in both cases anyway) – gregmac Dec 5 '15 at 6:46
  • @gregmac The heart of the question is, can I still use this box, so I'm interested in both cases. – JPhi1618 Dec 5 '15 at 14:28
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If the clamp breaks off, strictly speaking, the box is trash and should be replaced. In practice, there's usually a little latitude.

(I prefer metal boxes.)

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    inspectors look for broken tabs in my area. I agree with batsplaterson – Ed Beal Dec 4 '15 at 20:07

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