Romex into plastic boxes

[Nukedaddy]

There are several makers of switch and junction boxes using PVC or other resins acceptable to code. The code requires the romex to be restrained by a staple or ? Within a few inches of the box. OK so far?
Some brands are obvious how to get the romex into the box as they have a simple rectangular knockout to remove completely. BUT: What about the others? Some have what appears to be a resilient clamp that still must be cut or pried open that seems to be intended to clamp/restrain the romex where it enters the box. Some have what may be a 2 part knockout, but is angled inward the box and may have some clamping function.
What is common to most or all the brands is a complete lack of instructions or any guidance on what is the intended method. Cut it out, bend it in or stare at it in grief. It would make a preacher cuss on Christmas!
All these boxes are sold the same way, in bulk or singly in bins at big box lumberyards with no directions.
Has anyone seen and can share the maker’s “right” way to work the clamping types? Maybe share a link to a brand video? Like I said earlier, the ones that are clearly intended to cut/knock out are not an issue. Only the devilishly designed clamp-like critters vex me. I think some are Thomas & Betts, some Carlon, some Others.
Also. If the thingies are cable clamps, and installed correctly, does the code credit them as cable restraint and remove the need for a staple nearby?

 

[hj]

Push the wire through the opening and it will "retract' the clamp so the wire can go trough it. Use the staple.

 

[Sponsor]

 

[Nukedaddy]

What brand? I have tried that. The clamp thingy is too stiff. To even get the wire in I had to cut away a molding sprue and then forcefully pry the clamp just to get the cable into the box. After prying to get it open enough to pass the wire, the plastic was permanently deformed and stayed bent, with no clamping effect.
One of the ones frustrating me is “LeGrand” brand from Pass & Seymour, it can be seen on the Home Depot website. It is described as a clamp type. I bought several. All had to be carved or knocked out with screwdriver and hammer. None had any directions for use.

 

[wwhitney]

NM cable needs to be clamped to the box, and secured within 12" of the box. The exception is that with a single gang box, you can forego clamping to the box if you staple within 8". [Distances from memory, check NEC Article 314, I think.]

So you'll find single gang plastic boxes have the larger piece you remove and there's no clamping effect. On the plastic clamps, they are tricky to use; generally you have to sever a small bit of plastic at one end, then you can push the wire through the resulting gap. I often use a small flat screwdriver and give it a whack.

If you do overdeform the plastic clamp so it no longer clamps, you can generally deform it back to closed and end up with at least a little clamping action. Overall the clamps don't work so well.

The clamps on fiberglass boxes work a bit better. There you make a hole in the fiberglass, but there is a separate plastic piece inside that is wedged between some restraints and acts as the clamp. The plastic piece is removable, if I recall, and so it doesn't get deformed when make the hole in the box.

Cheers, Wayne

 

[Norcal01]

Single gang boxes do not require clamps & must be stapled within 8", 2 gang & larger do require clamps & be stapled within 12".