Melted socket, plug and wiring

[strength_10]

Hello. Long time reader but not many posts. After more of a bit of insight than anything else as I have asked for a local electrician to come and have a look next week (unless anyone reading is near BS39 in Bristol/Bath and wants to have a look).

I have a washing machine (couple of weeks old as previous one had bearings failing) and a tumble dryer in my utility room. Both appliances are individually plugged into single sockets under the counter which are separately fed from 2 FCU above the worktops. Both FCU are fitted with 13A fuses. Have been happily (I think) like that for 6 years since the house was rewired and had new consumer unit fitted just after we moved in and had solar panels installed.

Couple of days ago washing machine stopped working. Assumed it was an unlucky new appliance to Samsung sent out an engineer. He spotted (quickly) that the plug was damaged and the socket starting to melt through. He then spotted that tumble dryer plug was even worse and socket properly melted through. Good news is the new washing machine doesn't seem to be broken after all. Bad news is both sockets and both appliance plugs are broken. I removed the fuses from FCU, isolated the MCB and unscrewed the sockets to find wiring inside is blackened and a bit melted.

Obviously I'll need the wiring and sockets replaced and the circuits tested but I'm after a bit of insight (I appreciate it's a bit of guesswork from afar) as to:

a) what causes this sort of damage?
b) why it may have happened to 2 separate sockets and plugs being fed from 2 different FCU feeds in short succession?

Thanks in advance,
Cameron

 

[Octopus]

On a different note, is there any benefit in asking for the replacements to be flex outlets as they are fixed appliances which don't really get moved rather than plug and sockets?

If you have fused spurs above the work top then flex outlets make perfect sense ....

 

[telectrix]

If you have fused spurs above the work top then flex outlets make perfect sense ....

and a cooker outlet plate would not fail with only 10 -11 amps going through it's 40A terminals.

 

[MJPD29]

Definitely don't think new mk are any good.

3 G switch last week, unable to do up 6 of the screws..... Off shore manufactured carp

That's why I said old mk. Have you tried their new split boards? I was adding a cooker circuit into one already installed to find 4 of the screws in the neutral bar had sheared when the original installer had fitted it, the breakers don't sit straight and the screws in the lid barely line up. So disappointing

 

[MJPD29]

.

 

[Marvo]

We get enquiries about burned plugs and/or sockets quite regularly, here's another from a few weeks ago

One of my theories was/still is if appliances don't get unplugged once in a while the plug pins and receptors in the socket get tarnished which makes them higher resistance causing heat which then makes the receptors lose tension, in turn causing arcing.

If a plug is removed from time to time it wipes clean the brass contact areas on the pins and in the socket making it more reliable.

 

[Lucien Nunes]

Yes, although with good-quality fittings the contact should be gas-tight enough not to fail so often. Contact wiping is a work-around for poor design and poor materials. Failure of spring temper can be an integral part of the runaway process too:

Contact is loose - surfaces oxidise.
Oxidation increades resistance, contact heats more.
Heat weakens spring tension, contact gets looser...

 

[Marvo]

I'm sure there's lots of other contributing factors. I think that with a lot of the newer sockets it's simply that they've trimmed and trimmed the amount of brass to the point where contact tension has suffered. The quality of brass being used could also be an issue. Also if the socket is located below counter at the back of the washing machine and tumble dryer then humidity could also be high and accelerate corrosion.

 

[Midwest]

That's why I said old mk. Have you tried their new split boards? I was adding a cooker circuit into one already installed to find 4 of the screws in the neutral bar had sheared when the original installer had fitted it, the breakers don't sit straight and the screws in the lid barely line up. So disappointing

He should of use a torque screwdriver, and he wouldn't of had that problem

Incidentally, MK reckon they've cured their wonky mcb's etc with their latest A3 CU's!

 

[Solarmark]

Hi not looked at this forum for a while but just picked up my login details and saw this post.
I’ve read all the feedback and there are some good points.
I can’t remember who posted it, but the person who said just get decent quality sockets like MK is quite correct.
Having been in the electrical trade over 27 yeasts I have like many other electricians installed non branded sockets. When you talk to the Wholesailors where you purchased from, they will tell you either, “they are all made in the same place” or “they are all made the same way”
Unfortunately it’s not until you see pictures like yours that you see their not !
When you get burn or flash or scorch marks like the ones on your pics, they indicate the point of highest resistance and quite clearly point to where the failures is.
You won’t find scorch marks on a socket if someone has not tightened a terminal under the floorboards properly.
It is nothing more complicated than that.
If you are in a area or location with a high grid voltage and or, the items you described are quite energy consuming units then you would be better to have fixed points put in.
Otherwise you would be fine with decent quality sockets and manufactures plugs, providing you don’t have excessive moisture or water ingress near to or around the sockets.
This happened to one of our customers who has one of these instant hot water tap things that the heater was Ged from a socket under the sink with a slight leak that kept blowing the fuse.
I hope this helps and good luck

 

[telectrix]

the instant heat under sink jobbies i've fitted lately are 9kW. 40A MCB, 6.0mm cable, and a 40A isolator.

 

[MJPD29]

He should of use a torque screwdriver, and he wouldn't of had that problem

Incidentally, MK reckon they've cured their wonky mcb's etc with their latest A3 CU's!

I don't use them but I'll have to keep an eye out for the next new one I see! Seems to be quite a few brands can't make it work, poor build quality really

 

[Midwest]

I don't use them but I'll have to keep an eye out for the next new one I see! Seems to be quite a few brands can't make it work, poor build quality really

Their new RCBO's are a nightmare to terminate cables in. Don't use their CU's no more.

 

[Gavin John Hyde]

Definitely don't think new mk are any good.

3 G switch last week, unable to do up 6 of the screws..... Off shore manufactured carp

MK quality has really gone down hill the last couple of years, lots of jammed terminal screws in the back and things just seem a lot looser than they once were.

 

[Gavin John Hyde]

We get enquiries about burned plugs and/or sockets quite regularly, here's another from a few weeks ago

One of my theories was/still is if appliances don't get unplugged once in a while the plug pins and receptors in the socket get tarnished which makes them higher resistance causing heat which then makes the receptors lose tension, in turn causing arcing.

If a plug is removed from time to time it wipes clean the brass contact areas on the pins and in the socket making it more reliable.

That was my job, was a washing machine that was used sometimes twice a day and always left plugged in. replaced the socket with a Hager and they have had no issues since.

 

[Octopus]

All of this suggests that putting the sockets for high-power appliances above the work surface where they can easily be seen is a sensible option.

Definitely not behind them ............