Mark Lloyd wrote:
On Mon, 19 Dec 2005 17:57:42 -0600, RP
wrote:



Ralph Mowery wrote:

"Travis Evans" wrote in message
news:BmHpf.437$Cw5.54@fed1read05...


On Monday 19 December 2005 12:43, Mark Lloyd wrote:



BTW, considering strange electrical stuff, what if you had an old
(Edison base) fuse box that you could screw a light bulb into instead
of a fuse?

When I was young (not too long ago) I read in some sort of "home
emergencies" type of book something to the effect that you could screw
in a light bulb in the fuse box to locate or diagnose a short. The
bulb would glow brightly when there was too much current going through
it.

I'm guessing that if you screwed in a light bulb in a fuse box, the
brightness or dimness of the glow would depend on how much current was
being drawn on that circuit.



That is true. While I don't recommend it to people that are not use to
working with electricity, a trouble shooting practice is to subistute a lamp
with for the fuse or breaker. If the circuit is suspose to be open the
light will not burn. If you put in a 100 watt bulb in a 120 volt circuit
and it lights up to full brightness then you have a short circuit or some
device in the circuit that is drawing current. If you are sure there is
nothing in the circuit you look around and disconnect things tuil the light
goes out. If there could be a high current (more that an amp or two) device
in the circuit, you will have to disconnect it. Anything in the circuit
that uses less than a couple of amps will cause the light to burn dimmer.

Sounds like a good way to burn down a house or to smoke a few small
appliances. For an encore you can slip a penny under the fuse. Dear
readers, please don't try any of this at home!



Are you somehow equating a penny and a light bulb? A light bulb has a
much higher resistance, and (unless it got shorted somehow) could
never (on 120V) pass a current higher than 833mA (for a 100W bulb). It
wouldn't even conduct that much unless it was into a shorted circuit.

I used to work at Goodwill (for awhile), and they actually used light
bulbs in series for testing appliances.

Two reasons its a stupid idea:
Suppose the ohmic resistance of the light bulb is 240ohms (60watt
incandescent). Now suppose that the resistance at the short is 240ohms
when you have the bulb in place in the fuse box. Each load drops 60
volts for a total of 15watts dissipated at the short. Now suppose the
short is where a wire nut has fallen off. The wire junction has gotten
next to the fart fan housing and is arcing to the paper thin sheet
metal. There is a paper label inside the housing of the fart, opposite
the short, and the arcing sets this paper on fire. How long to you
think it will be before 15 watts continuously dissipating will get a
junction hot enough to ignite any combustible materials adjacent to it?
Arcing shorts can cause fires, and are in fact responsible for a large
number of electrical fires every year in the real world. The odds may be
against a fire starting in any one particular instance with this method
of short detection, but I'd hate like hell to be that one in
ten-thousand statistic on anything that I was diagnosing.

Now let's suppose that there is a small appliance plugged into an outlet
on that circuit. The voltage dropped across that appliance will vary
from 0 to 120 depending upon its resistance and upon the nature of any
upstream short which can vary from 0 to infinity ohms. Most appliance
won't be harmed with continuous low voltage for 5 to 30 minutes, but
some will. I also wouldn't want to be responsible for a smoked
electronic or motorized appliance.

A volt/ohmmeter can be obtained from any Walmart store for $10, (or
1,000 pennies even).

hvacrmedic