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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:

enter image description here

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?

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    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
    Commented Dec 4, 2015 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
    Commented Dec 4, 2015 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
    Commented Dec 5, 2015 at 6:46
  • @gregmac The heart of the question is, can I still use this box, so I'm interested in both cases.
    – JPhi1618
    Commented Dec 5, 2015 at 14:28
  • Plastic gets brittle when it gets old and if the tabs break off, the box should be replaced. On a newer box, you can hoik on the tabs all day long and they don't seem to fatigue easily.
    – AdamO
    Commented Oct 12, 2023 at 15:03

2 Answers 2

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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
    Commented Dec 4, 2015 at 20:07
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I hate the tabs and cut them off. They have very sharp edges which will cut through the wire sheath in time. Plus, when initially pushing the wire into the box, you may need to pull some back out and it's impossible and already dug itself into the sheathing. I cut them off.

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    If you do this, you may very likely fail a rough-in electrical inspection. Not only do cables need to be clamped entering the box but the manufacturer's NRTL listing is based on use and installation according to the design of the product. Finally, unnecessary or unused openings in electrical junction boxes are not allowed. This is bad advice. If you don't like the integrated clamps on common plastic boxes, use metal boxes instead.
    – RibaldEddie
    Commented Apr 5, 2023 at 18:39
  • Think that's annoying? How about tripping over the wire in the attic and yanking the live wire right off the receptacle!
    – AdamO
    Commented Oct 12, 2023 at 15:02

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