To backstab or not: what the code and lab testing say about push-in receptacle connections

The r/electricians thread opened with an electrician who gave up backstabbing after criticism and says he has since seen service calls for burned push-in connections. The method is legal, within limits that are easy to miss on a fast trim-out.

The 2023 National Electrical Code added section 406.3(D)(3) to state those limits plainly, Robert Fahey, chair of Code-Making Panel 18, wrote in IAEI Magazine. Push-in terminals may be used only on branch circuits of 15 amps or less and only with 14 AWG solid copper, unless a device is listed and marked for other conductors. UL's guide information for receptacles says the same and rules out aluminum, copper-clad aluminum, stranded 14 AWG and all 12 AWG wire. A 20-amp circuit run in 12 AWG cannot go into those holes.

Back-wire clamp terminals are a separate category. In a 2008 answer published in IAEI Magazine, UL said screw terminals, setscrew terminals and back-wired clamps tightened by a screw are all suitable for solid or stranded building wire. Push-in holes carry no such rating.

On failures, the most detailed public testing covers loose connections in general. A study for the National Institute of Justice by Matthew Benfer and Daniel Gottuk, published in 2013, ran 528 receptacle trials, 408 of them on terminal connections. It found that "only the loosest connections" developed significant overheating, regardless of what the receptacle was made of or how it was installed. The study did not rank push-in terminals against screw terminals.