The second rule is a great one that so many people doing their own work miss.
The wire nut is only there to stop the wires loosening over time and provide some basic insulation. It is not there to actually attach the wires. When you twist your wires together, they should be attached well enough on their own that you'd be comfortable throwing a piece of electrical tape over them to stop them shorting to the box and leaving it as-is (but don't do that). If the only thing keeping them together is the wire nut and you being very gentle when you manipulate them back into the box, they're not actually connected.
The poor physical connection creates a poor electrical connection. A poor electrical connection has resistance which creates heat. Heat creates fires. Even better after a few years when enough traffic has driven past your house and enough people have moved around inside of it and the wires have wiggled to just barely in contact so occasionally when someone walks down the hallway the lights will all flicker as the wires create some pretty electrical arc light shows, adding carbon buildup to the wires and further increasing the resistance and heat concentrated in the one tiny point of the copper where they're still sometimes connected.
No reason at all for this rant. Definitely not a real example at all. Definitely didn't waste an afternoon with a toner, a drill with a pilot bit, and a borescope to hunt down the six octagon boxes someone had sealed into the basement ceiling hiding away some of the shoddiest wiring I'd ever seen. Nope.
100% confirm on the wire nut thing. It's possible to get a good twisted connection with a wire-nut without pre-twisting, but conditions have to be just right, and must result in a properly twisted wire pair in the end, or it's just trouble waiting to happen.
One packet of wire nuts I bought came with a drill bit made to twist them on. I found it works way better than twisting the wires by hand, it creates a tight twist that's very hard to undo.
This makes me feel bad. As a kid, I remember holding light switches at just the right point to hear the buzzing (arcing)? inside. At least if the contacts were carbonizing, there wasn’t a lot flowing through them closed.
The wire nut is only there to stop the wires loosening over time and provide some basic insulation. It is not there to actually attach the wires. When you twist your wires together, they should be attached well enough on their own that you'd be comfortable throwing a piece of electrical tape over them to stop them shorting to the box and leaving it as-is (but don't do that). If the only thing keeping them together is the wire nut and you being very gentle when you manipulate them back into the box, they're not actually connected.
The poor physical connection creates a poor electrical connection. A poor electrical connection has resistance which creates heat. Heat creates fires. Even better after a few years when enough traffic has driven past your house and enough people have moved around inside of it and the wires have wiggled to just barely in contact so occasionally when someone walks down the hallway the lights will all flicker as the wires create some pretty electrical arc light shows, adding carbon buildup to the wires and further increasing the resistance and heat concentrated in the one tiny point of the copper where they're still sometimes connected.
No reason at all for this rant. Definitely not a real example at all. Definitely didn't waste an afternoon with a toner, a drill with a pilot bit, and a borescope to hunt down the six octagon boxes someone had sealed into the basement ceiling hiding away some of the shoddiest wiring I'd ever seen. Nope.