The element in our hot water cylinder failed yesterday (didn't quite
make its 19th birthday) and an electrician came today to replace it

Looked OK on the outside. Clean, shiny. But, oh, the horrors on
the inside. A little corroded. Just a little

http://home.clear.net.nz/pages/joecolquitt/element1.jpg

http://home.clear.net.nz/pages/joecolquitt/element2.jpg

Looks like a nasty surgery thing I saw on Discovery

This must be long-standing corrosion and it absolutely amazes me
that it has taken until now to pop the circuit breaker. Surely the
winding must have been wet before yesterday. After it dried, most
of the filler just fell out. My nephew up north is doing an electrician's
apprenticeship and says he sees that sort of breakdown regularly

So I was chatting with the sparkie, as you do, and asked him why
the damage was closer to the Active/Live connection. (you can see
in the first picture that the damage pretty much stops where the
element turns around, ie halfway between A and N). He couldn't
say. He said that he asked once at college why, if the current is
AC, that Active and Neutral aren't regarded as interchangeable.
But the answer he got was "they just aren't"

Anyway, I've wondered about it too. I've thrown out IEC leads,
like on the kettle for example, because the Active connection has
suffered heat and corrosion damage. I'd have thought that elements
are more or less just resistive, nothing complicated wrt power for
example

Why does the corrosion happen that way ?

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist