I mostly use NM boxes, which are typically the blue Carlon. I can't stand the internal clamps on them. I was using the round ones to install smoke detectors, and I had so much difficulty feeding in the 12/3 NM. I don't remember having as much difficulty with the 1 and 2 gang boxes, but it may have been because I was using 14/2. I ended up pulling the clamp with my linesman pliers, so that I could feed the cable through. I never realized it before, but I actually like metal boxes better. It seems like it's so much easier to feed the cable. Having to ground them is a minor nuisance and one that I don't mind. Is there a trick to the internal clamps? I know it's probably a dumb question, but it seems like it shouldn't have been that difficult.

 

I'm with you in that steel boxes are the way to go 95% of the time unless you are chasing pennies wiring a new tract home.

I believe the rule with single gang blue is that you can remove the clamp as long as you secure the cable within 8" of the box.

 

I loosen the tabs slightly with a straight blade screwdriver if the cable doesn't push in easily.

 

That is correct. Usually on a single gang box they are actually a knockout.

I have problems with the multi gang boxes. Those clamps either won't open correctly or snap off if opened too far. I recently did a "rough" in the cold.

 

Single gang device boxes do not have clamps. The multigang boxes have clamps.

 

I usually loosen the clamp a little with the tip of my romex stripping tool then bend a slight curve into the romex the long way before pushing it into the box. It helps avoid running into the other side of the box or the opposite clamp. On the really tight boxes like the 18 cu rounds, I usually push the cable through about an inch, then reach in the box with needlenose and pull it through the rest of the way.