David Nebenzahl wrote:
On 8/29/2009 2:38 PM Roger Shoaf spake thus:

"David Nebenzahl" wrote in message
s.com...

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.)

Lets say you have a light fixture with a 100 watt bulb. Inside the
fixture
they use the smaller wires and something shorts out. Those wires are
encased in the fixture and the box. The short circuit lowers the
resistance
and the amps shoot up and the breaker pops. The excess heat from the
short
is contained and dissipated in the metal fixture long before it causes
mischief.

Now consider a different proposition. The circuit has a penny in the
fuse
box and the circuit is overloaded. The wires inside the walls heat up
and
catch the house on fire.

That makes sense; the idea is to confine any potential fires within
boxes, where they presumably won't burn the damn house down.

Which is why I use metal boxes instead of plastic ones, and pay
attention to properly clamping cables going into the box (rather than
just sticking the cable through a hole in the box).


Hmmm,
Is there anyone who does not do that when wiring? Then it'll fail
inspection. Every thing is simple math and cool head. Actually life is.