OK, here's today's electric circuit puzzle:

Client wants a new ceiling fan installed. The old one works, they just
want a different one up there. No problemo, right?

The new fan has a light, just like the old one (actually several hanging
sockets). Unlike the old one, though, the new one has only 3 wires: hots
for the fan and light, and a common neutral. Ugh. Not the way I would
have designed it.

I hook it up, figuring that I can simply use one of the neutrals in the
ceiling box and not the other one. Try it: light doesn't work at all,
while the fan does. That's weird.

So I go up there and measure voltages between wires. Here's what I get
(apologies to those who don't use monospaced fonts):

(1) blk X---- ----X blk (2)
fan light
(3) wht X---- ----X wht (4)


Measured voltages:

1 2 3 4
-------------------------------
1 90* 120 240
-------------------------------
2 90* 0 90
-------------------------------
3 120 0 120
-------------------------------
4 240 90 120
-------------------------------

* The 90 volt readings are from the dimmer switch all the way up.


Hmmm; something ain't right.

I ended up putting the old fan back up, as I couldn't get to any of the
wiring above the ceiling and we decided to leave well enough alone.

I figured out what was wrong after I got back home. It's actually pretty
simple.

For the solution, look he
http://www.geocities.com/bonezphoto/...redCircuit.gif


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair