On Sun, 7 Sep 2008 07:33:25 +0000 (UTC), Dave Martindale wrote:
AZ Nomad writes:

Few people have a single meter with a sufficiently low-range ohms scale
at home, but you can still do it with a bit of ingenuity. If you pass
a constant current through the wire, you get a voltage across the ends
that is proportional to the wire resistance, and many DMMs (even some
of the cheapest ones) have a 200 mV scale. For example, with a 1 A
current source, the two 10-foot pieces of wire in the example above
would have a voltage drop of 16 and 25 mV, enough to be told
apart by a DMM on even a 2 V range.

That is the basic gist of a 4 wire probe. With one pair of leads, put some
current through the resistance under test. a 10V supply and a 100ohm resister
will put 100ma through and be fairly immune to the resistance of the first
set of probes. Measure the current going through the first pair of leads
(or it has to be regulated). With the second set of probes, measure the
voltage drop across the resistance under test. R=E/I.

That's more or less where I got the idea. The difference is that the
pair of measuring probes could move along the "resistor" and observe
the voltage drop. The amount of voltage drop between two outlets is
reasonably correlated with the length of wire between them.

If you're measuring resistance between outlets, you could plug in a small
resistive load like a 25W bulb and slap on a clamp on amp meter to
know the current through the circuit. Then you could measure the
voltage drop between outlets and know the resistance. To get from
there to the wire gauge, you'd have to know the length of the wiring
between the outlets.