The sub-thread up yonder about using 15-amp switches on 20-amp circuits got me to thinking. Actually, have been wondering about this for a long time, so here goes.
The thing is, we have circuits where the wiring and devices on that circuit are designed to safely carry a certain amount of current, for example a 15-amp circuit using devices rated for that amount and wired with #14 wire. All well and good.
But our discussions here inevitably leave out what I'm calling the "last inch". By that I mean such things as the wires that feed a lighting fixture, attached inside the wall or ceiling box, or the wires connecting a dimmer switch. These wires are always a *lot* smaller than the cable used to wire the circuit; often they're around 16 or 18 gauge.
This would seem to violate the integrity of the circuit, because now you have weak point. In the worst case, a short circuit at the device, you'd have a lot of current going through these smaller wires, until the breaker trips. Isn't there a greater chance of fire in that case?
So how does the NEC reconcile this apparent violation of the integrity of the circuit? How do folks like us who install and work on such wiring rationalize it? Is it simply a matter of practicality? (It's obviously not practical to use 14-gauge wire all the way up to every device on a lighting circuit.)