DIYbanter - View Single Post

DT

In article m,
kens says...
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?

They specifically allow the smaller gauge wire within a fixture, and
reconcile it by permitting the fixture manufacturer to act as the
"Authority Having Jurisdiction" and testing their own fixtures. The
fixtures must remain an "end device", and cannot have anything wired in
series with them. The short length of smaller wire is proper for the
limited current draw.

I believe the code used to allow 14 gauge "drops" in 20 amp circuits,
which were runs from switches to lights with the similar logic that a
light would never draw more than 15 amps.

--
Dennis