Russell McMahon writes:
>If you are terminating wires using screw down terminals (chocolate blocks,
>terminal blocks, rising clamp connectors, ....) you should NOT solder the
>whole end.

        An excellent point.  Again, when I was fixing tape recorders
and film projectors for our Audio Visual department, we often replaced
the AC or mains plugs on equipment when the cord was damaged or
somebody had cut off the Earth prong or, in some cases, pulled it out
with pliers, fearing it might grow back.:-)  We started tinning the
new wire in the cord before tightening the screws down.  It looked so
neat.  A few months after doing this, equipment we had fixed started
coming back in with loose connections on those plugs.  It was
instantly obvious what kind of monster we had created so we quit doing
that immediately.  Sometimes, the road to Hell is paved with good
intentions.  I hate to say it, but I may have even been the one to
suggest tinning and everybody else thought that sounded good.
Everybody there was technically competent and it was just one of those
good ideas that wasn't appropriate for the situation.

        On the topic of dissimilar metals which has also appeared in
this thread, I remember the big scare over aluminum house wiring which
occurred in the United States during the seventies or so.  Lots of
houses were wired with this stuff and they began to burn down after
people incorrectly installed fixtures rated for copper wiring on the
aluminum cables.  The gauge of the wire was slightly larger to begin
with and so it didn't fit well under the screw.  A little thermal
cycling and electrolysis of the aluminum/brass junction would create a
resistance heater which would one day get red hot and start a fire if
someone connected anything substantial to that outlet.

        I think aluminum is still used in the service drop from the
pole to the meter, but those connections are especially designed for
the purpose and I don't believe there is any particular problem with
them.

        Another thing about dissimilar metals.  We used to live in a
house that was built in 1951.  Some time in the mid sixties, the
previous owner replaced the galvanized steel pipe with copper
plumbing.  Somebody didn't know what they were doing for they attached
the new copper line to the house to a steel fitting on the meter
without an insulating fitting.  One evening, we came home to find a
note from the city on our door saying that they had turned off our
water during the day because a flood had burst forth from the meter
and was flowing in to the street and freezing.  All because of
galvanic action over 20 years between the copper and the steel of the
fitting.

        The same bright soul who did that also used a steel reducer in
the kitchen on each copper line to the sink and I was lucky in that I
discovered those when replacing the faucet, one day.  The hot fitting
was much more corroded than was the cold water line, probably due to
the heat accelerating the electro chemical activity.  It looks like
steel becomes the cathode in one of these little batteries from Hell.

Martin McCormick