Melted socket and plug

28 Apr 2007
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United Kingdom

I have a washing machine pluged into a socket inside my kitchen cupboard. The washer went wrong so we got a new one, on removing the old washer we found that the face of the socket behind the plug had melted and turned brown and the plastic around the pins of the plug had melted including the black bands (safety plug) allowing the pins to wiggle.

The socket looked perfectly normal until the plug was removed and could have been like it for months without realising.

Just wondering what caused this?

p.s. the socket has been replace and the wire behind was fine and the cause of the washer to go wrong was a faulty motor sensor.
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most likely a wire was not tightly gripped in its terminal. This creates a high-resistance joint which gets hot, as it gets hot it gets looser, so hotter, so looser. Eventually the junction between the wire and the terminal will burn away.

This most often happens with heavily loaded connections, such as the switches for electric showers. For some reason it more often happens with the black neutral wire.

The end of the wire that overheats is damaged by the heat and softened so that it will not form a good connection in future, so will overheat again. So the discoloured end needs to be cut off back to bright metal. Professional electricians have a tool to put a new end on if the wire is too short after cutting back (it needs great pressure to do it properly).

Was it a single socket, or a double?
another cause i've heard is the pins not being gripped tightly enough in their holes, creating a high-resistance connections between the plug and socket.

Also corrosion and muck on the pins.
Ah that's why in the old days appliances like washing M/Cs were wired into a fused outlet. I was told by an old time served sparky that fixed appliances should never be plugged in as the design of the 13A plug and sockets cleans the contacts as you unplug and plug in.

Cause of socket failure was put down to a certain amount of corrosion and weakening of the contacts which will eventually cause some minor arcing leading to a build up of carbon which then increases arcing and heat until one day they overheat to a point when thay fail.

But these days as soon as you cut the plug off to wire into an outlet you invalidate the appliance warranty
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I took apart a 3-way adaptor block the other day. The pins are very brown, not shiny at all, because they haven't been inserted or extracted in so long.

And the socket contacts inside have a very small surface area, I wouldn't say they are rated for 13 amps. Again very brown and dull. Whenever a plug is inserted, it sparks because of the high resistance.

Its going in the bin, i've never liked 3 way blocks.

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