On Tue, 09 Sep 2008 18:04:17 GMT, "The Medway Handyman"
wrote:


The metal wipers in the socket holes do not touch the pin over a big
enough area or firmly enough to give the minimum contact resistance
or cut through surface dirt/oxidation. This leads to heat and more
oxidation, leading to more heat.

This can happen over time with a decent socket - it never hurts to
unplug and plug back in every now and then (once or twice a year) to
remake the contact. Also loose wires inside a rewirable plug (not
usual on a washing machine now) can cause the same heating problem -
check screw tightness too if the plug is rewirable.

Are they not all made to a British Standard spec? I would assume that laid
down minimum contact areas?

It may or may not. As regards the sockets the actual area of contact
is governed by the profile of the contacts after they've been pressed
into the required shape and concealed within the plastic assy. Of
course the quality of the metal contact material is also significant.

Plenty sold on market stalls and in pound shops are counterfeit.

Sometimes stuff is claimed to be made to a BS spec (so that's all
right) but in fact has never been tested by an independant test house,
you've only *Their* word for it that it complies. Sometimes stuff is
type tested and passed but then the production methods are not
sufficient to ensure consistency of the product over the years of
production. For instance a colleague once went to China to install a
Swiss metal casting machine and found the "factory" had four walls and
a roof but just an earth floor. His precision casting machine weighed
3 tons. A famous local manufacturer of electric motors moved
production to Poland and found the rate of warranty failures and
customer complaints suddenly went through the roof. They sent somebody
over and found the "factory" was unheated and the operatives were
assembling motors in the Polish winter wearing overcoats and gloves.

Imagine how much of a mess a back street sweat shop in Bangalore could
make of a 13A socket.

Derek