Rule 28 of 40 · Chapter IV — Conductors and Loads
Use screw terminals, not backstabs
Why this rule exists
Many receptacles and switches offer push-in backstab holes that grip the wire with a small spring behind the plastic. They are fast, and they fail. The contact area is tiny and the spring tension fades, so under load the joint heats, and backstabbed connections are a well-known cause of intermittent power, arcing, and burned devices. The screw terminals on the same device clamp far more copper with a controlled, torqueable force. Same device, two ways to connect it: one built to last, one built to install fast. Choose the one that stays cool under current.
In practice
Terminate on the screw terminals: wrap the conductor clockwise three-quarters around the screw, or use the back-wire clamp type that a screw tightens down onto the wire, not the spring backstab. Torque to spec. If you open a device and find backstabbed connections, especially on a circuit that is misbehaving, move them to the screws. Prefer devices with back-wire clamp plates for stranded and solid alike. Reserve push-in connections for the low-current signal work they suit, never for general-purpose 15- and 20-amp power.
When it doesn't apply
Some higher-grade back-wire devices use a screw-actuated clamp plate rather than a spring, and those are reliable; the problem is specifically the spring-grip backstab, not all rear connections. Certain listed lever and push connectors for splicing are engineered differently and perform well. The distinction is the mechanism: a controlled clamp is fine, a fading spring is not.