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Todays Puzzler.The mystery of electricity - Page 2

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Posted by j on June 1, 2012, 5:43 pm
 
On 5/31/2012 4:06 PM, j wrote:

I took apart the fixture today and found out why. Let's review the
evidence:


Note the "one piece".
 >
Common at one time.

Note that the fan worked fine, it's not that it struggled on partial
voltage, and if it was wired in series, the bulb (an incandescent) was
completely dark.

This removes the series connection theories. And certainly the 220v
theory that depended on it.

So, what we have in the socket in the dead middle is a U shaped flat
copper strip. The hot wire is soldered to this and each end of the U
contacts a bulb center contact. For the ground threaded part: there are
two of these with a solder tab. They are facing outward, of course, but
the tabs are together and the ground wire is soldered to the left socket
that had the bulb screwed in. The tabs are in turn soldered to each other.

So, what happened?

The connection between the two tabs broke apart. When the bulb was
screwed in it pushed it's ground tab out enough to contact the other tab
and send power through it's "ground" connection.

The winner is: Jim Wilkins

Why didn't the bulb light? The "hot" contact was oxidized enough to be
an insulator.


I have pics and video...

   Jeff

  Unscrew the bulb and the fan turns off.


Posted by Winston on June 1, 2012, 9:18 pm
 
j wrote:

Thanks for closing the loop, j.
Well done, Jim.

--Winston

Posted by Jim Wilkins on June 2, 2012, 12:56 am
 

Bad grounds and intermittent connections cause the oddest symptoms.

In Army Signal Corps electronic school the instructors doctored AGC
glass fuses to remind us to check them with a meter, not just by
sight. They heated one end cap to melt the glue and pop off the cap,
then inserted too-short heavy bus wire and even blue ("the fuse blew")
paper to make it look good again. I caught the 1 Amp fuse with 12 AWG
wire inside it visually and went up to joke with the instructor about
it, then we watched most of the class pull out the phony fuses, give
them a puzzled look, put them back and continue troubleshooting.

jsw



Posted by m II on June 2, 2012, 3:20 am
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Jim Wilkins wrote:


Fuses on electric stoves/ranges are bad for that. They commonly break
the link where it bends, just outside of sight. The fuse looks good
through the glass, but there's no continuity.

The repeated cycling off/on and the resultant thermally caused
expansion/contraction probably work hardens the metal where it's
already been stressed by the bend, causing the fractures.

So, yes...using a meter is a very good idea.


mike






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Posted by Mho on June 3, 2012, 2:28 am
 Stick with your failed Internet business.

------------
Fuses on electric stoves/ranges are bad for that. They commonly break
the link where it bends, just outside of sight. The fuse looks good
through the glass, but there's no continuity.

The repeated cycling off/on and the resultant thermally caused
expansion/contraction probably work hardens the metal where it's
already been stressed by the bend, causing the fractures.

So, yes...using a meter is a very good idea.


mike



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