Does the NEC prohibit backstab connections?

No. The NEC has no article banning push-in terminals. Section 110.3(B) requires the device to be used per its listing, and the listing on most residential receptacles limits the push-in hole to 14 AWG solid copper.

Can I backstab 12 AWG wire?

Not on a typical residential device. The stripe gauge and marking on the back read 14 AWG solid only, so pushing 12 AWG in violates NEC 110.3(B). Use the screw terminal instead.

Is a back wire clamp device the same as a backstab?

No. A back wire device uses a steel pressure plate tightened by the binding screw and is usually listed for 14 through 10 AWG solid and stranded. A backstab uses a spring blade with a much smaller contact area.

Are backstab connections on receptacles code compliant?

Yes, backstab terminations are code compliant, but only inside a narrow window. The NEC does not ban push-in terminals anywhere. What controls the install is Section 110.3(B), which requires listed equipment to be installed and used in accordance with any instructions included in the listing or labeling. On a standard residential receptacle, that listing is what limits the backstab hole to 14 AWG solid copper.

What the listing allows

Look at the back of any 15 amp residential device. Next to the push-in holes you will find a stripe gauge and small print that reads something like "14 AWG solid CU only" or "use No. 14 solid wire only." That marking is part of the listing under UL 498, and Section 110.3(B) turns it into an enforceable code rule. Push 12 AWG into a hole marked for 14 AWG and you have a violation, even though nothing in Chapter 2 mentions backstabbing by name. The same applies to stranded conductor. Almost no push-in terminal is listed for stranded, so a stranded 14 AWG THHN pigtail belongs on the screw, not in the hole.

Section 110.14(A) is the general terminal rule. It requires connection by means of pressure connectors including set screw type, solder lugs, or splices to flexible leads, and it requires the terminal to be identified for the conductor material and for more than one conductor where two are landed together. A listed push-in terminal is a pressure connector, so it satisfies 110.14(A) on its face.

Backstab is not the same as back wire

Field crews use both terms for the same device and they are not the same thing. A backstab uses a small spring blade that bites the side of the conductor. A back wire or clamp type termination uses a steel pressure plate driven by the binding screw, so the conductor is captured across a wide flat surface. Spec grade devices with the plate style are listed for 14 through 10 AWG solid and stranded, and they are mechanically far better than a spring blade. If you want speed without the spring, buy the clamp style device.

Why inspectors and service calls hate them

The spring blade contacts a tiny area of the conductor. Heat cycling on a loaded circuit relaxes the spring, resistance climbs, the plastic discolors, and eventually you get an open neutral or a burned yoke. Section 110.12 requires work to be executed in a neat and workmanlike manner and 110.14 requires terminations to be made so that good contact is secured. A backstab that is already failing will get written up on those sections even though it was legal at install.

Field takeaway

Backstabbing 14 AWG solid on a 15 amp circuit is legal. Backstabbing 12 AWG on a 20 amp circuit is not, because the device is not listed for it. Some jurisdictions add local amendments banning push-in terminals outright, so check your local rules before you wire an entire house that way. On any circuit you care about, land the conductor under the screw or use a clamp style spec device.