UK Melted Plug and Socket cause

[zerozero7]

Hi all,
Washing machine plug and socket melted around Neutral pin. Whilst removing socket faceplate, noticed one brown wire was not in the terminal. May have come out of the terminal when pulling the socket forward or may have been out all the time.
Is this lose or disconnected live cable the 'definate' cause of the overheating on the neutral pin?
Thanks, Gary

 

[Lucien Nunes]

That was my original thinking, lose or missing live overloading neutral?

No, this isn't how electricity works!

The location of the melting / burning clearly shows that this was due to bad contact between the plug pin and socket contact, and unlikely to have been due to loose terminals. Granted the line terminal was apparently loose because the cable pulled out, and a loose terminal can cause a burnout, but in this case it was unrelated.

All contacts rely on tiny (almost invisible) areas of metal actually making contact, so the current density is high and at least some heat is dissipated in the resistance. Less effective contact leads to more heat, which accelerates oxidation of the surface and weakens the spring temper of the socket contact gripping the pin. . This further reduces the contact area and it goes into runaway, leading to a burnout.

Good quality contacts are less likely to suffer from this effect and the socket is the main player rather than the plug. But progressive failure can still be triggered by some random adverse situation like a layer of deposit on the plug pin before installation, and some combinations of plug and socket metal alloys make better contact together than others.

Plugs that are regularly moved have the advantage that any oxide buildup is mechanically scraped off so that fresh bare metal surfaces are exposed. The same is true of the socket contact although heavy use eventually wears out the contact. Again, quality counts and the devil is in the detail, although price is a guide there is no cast-iron guarantee that the most expensive socket will last the longest in a particular application.

 

[zerozero7]

No, this isn't how electricity works!

The location of the melting / burning clearly shows that this was due to bad contact between the plug pin and socket contact, and unlikely to have been due to loose terminals. Granted the line terminal was apparently loose because the cable pulled out, and a loose terminal can cause a burnout, but in this case it was unrelated.

All contacts rely on tiny (almost invisible) areas of metal actually making contact, so the current density is high and at least some heat is dissipated in the resistance. Less effective contact leads to more heat, which accelerates oxidation of the surface and weakens the spring temper of the socket contact gripping the pin. . This further reduces the contact area and it goes into runaway, leading to a burnout.

Good quality contacts are less likely to suffer from this effect and the socket is the main player rather than the plug. But progressive failure can still be triggered by some random adverse situation like a layer of deposit on the plug pin before installation, and some combinations of plug and socket metal alloys make better contact together than others.

Plugs that are regularly moved have the advantage that any oxide buildup is mechanically scraped off so that fresh bare metal surfaces are exposed. The same is true of the socket contact although heavy use eventually wears out the contact. Again, quality counts and the devil is in the detail, although price is a guide there is no cast-iron guarantee that the most expensive socket will last the longest in a particular application.

Now that, is what I call an answer!
Thank you.
I guess my concern is that I stubbornly refuse to accept that a nearly new good quality plug and socket can fail so badly/dangerously! How many dangerous sockets are out there!?!
Maybe I should sent it to BG for their comment.
Thanks again

 

[Lucien Nunes]

We can't assume it was 'dangerous' by design or manufacture, because we don't know the actual underlying trigger mechanism for the burnout. Once it starts escalating, any high-resistance fitting can turn into a lump of melted goo, and it has been happening since the first days of electricity. A century ago, when plugs were often made of wood, they would char rather than melt but the result was not very different to what happened to your washing machine plug.

 

[jace999]

I just had that.Tumble dryer stopped.plug and socket too hot to tougch.stank of that burning electrical plastic smell.turned off supply.got plug out.neutral pin had black residue.changed fused,cleaned pin and worked okay in another socket.socket took a very long time to cool down.sparky booked,though tempting to have a look.Q Why didnt the RCD trip?The heat generated indicated that the fault was taking place long enough for the disruption to have been detected.

 

[jace999]

i had similar.tumbler dryer stopped.socket and plug stank and too hot to touch.turned off elec.took out plug cleaned off black residue on neutral pin changed fuse worked okay in another socket.sparky booked though tempting to look inside socket.fake fuses were an issue on domestic appliances a while ago,but old fuse not burnt.As the fault must have been evident for a while to generate such extensive heat which didnt the RCD trip?

 

[pc1966]

Q Why didnt the RCD trip?

RCD only trip if electricity goes "astray". Basically the look at the current going out on the L and coming back on the N, if they differ by more than a small amount (usually in the range of 0.015 to 0.030 amps) then they trip. As such they are intended to protect against electric shock, when often the person touches the L while in contact with the Earth and so some of the L current is not returning by the N as desired.

They can also protect against fires from partial cable faults when insulation is damaged and enough current flows to the CPC (earth wire, usually central in the flat "twin and earth" cable typically used in house wiring) to risk a fire starting, but not enough flows to trip the over-current protection device (these days normally a MCB = Miniature Circuit Breaker, but sometimes a fuse, when quick disconnection might need 100A or more fault current). Say crushed cable or rodent damage, even poor quality counterfeit cable.

Unfortunately they do not protect against overheating due to a poor connection. You can get AFDD (arc-fault detection devices) that are designed trip if the heating is caused by a tiny gap that is causing sparking (electrical arc) but they do will not pick up on a simple poor connection that is getting hot.

Quality parts and good workmanship, along with paying attention to any odd smells, sounds, or evidence of heating, are still the best defence for this particular problem!

 

[jace999]

RCD only trip if electricity goes "astray". Basically the look at the current going out on the L and coming back on the N, if they differ by more than a small amount (usually in the range of 0.015 to 0.030 amps) then they trip. As such they are intended to protect against electric shock, when often the person touches the L while in contact with the Earth and so some of the L current is not returning by the N as desired.

They can also protect against fires from partial cable faults when insulation is damaged and enough current flows to the CPC (earth wire, usually central in the flat "twin and earth" cable typically used in house wiring) to risk a fire starting, but not enough flows to trip the over-current protection device (these days normally a MCB = Miniature Circuit Breaker, but sometimes a fuse, when quick disconnection might need 100A or more fault current). Say crushed cable or rodent damage, even poor quality counterfeit cable.

Unfortunately they do not protect against overheating due to a poor connection. You can get AFDD (arc-fault detection devices) that are designed trip if the heating is caused by a tiny gap that is causing sparking (electrical arc) but they do will not pick up on a simple poor connection that is getting hot.

Quality parts and good workmanship, along with paying attention to any odd smells, sounds, or evidence of heating, are still the best defence for this particular problem!

Thanks for your clearly very knowledgeable reply.I am still shocked that the only safety feature that evaded a fire was my sense of smell and a small fuse in the tumble dryer plug.The safety regulations should be updated to include AFDD as a standard feature in new wiring installations and insurance premiums should reflect this in a reduction of premium.This wiring was only installed 4 years ago by a professional certified company.Even though the fuse disconnected current to the appliance,I can clearly see via the 3 plug pin entries that the internal housing of the socket is blackened and it is possible that a chain of events leading to a full blown house fire was already underway before all supply to the socket wiring was isolated.As we all leave several appliances on while we are away from home ,freezer etc why isnt this standard practice?The sparkys investigation will be revealing.I will get him to check all the other sockets too as the rewiring company blamed wiring difficulties on the age and location of my house . : ) : )

 

[pc1966]

Thanks for your clearly very knowledgeable reply.I am still shocked that the only safety feature that evaded a fire was my sense of smell and a small fuse in the tumble dryer plug.The safety regulations should be updated to include AFDD as a standard feature in new wiring installations and insurance premiums should reflect this in a reduction of premium.

While insisting on AFDD might seem like a good idea, in practice it is not necessarily so.

1) AFDD are not that good at stopping fires. They only add detection of an arc, and not overheating, and even the arc aspect is not that convincing (just search YouTube for John Ward doing some tests on AFDD). Also as I mentioned they do not stop fires from a simple poor connection or under-rated cable, nor would they stop fires from the likes of tuble dryers building up lint which as often classed as "electrical fires":

https://www.imperialclaimsconsultants.co.uk/faulty-whirlpool-tumble-dryer-recalls-increasing/

If they were a magic bullet to stopping fires, then why don't we see detailed analysis of what proportion of fires would be prevented?

2) They add a lot of cost. Sure that will no doubt drop in time, but today you could be looking at £2000 extra on the cost of a rewire or new CU. Now if you have paid off your mortgage and earn £50k/year that might not trouble you, but for the majority of folk that is going to make them think twice.

The unintended consequences of that are either poor electrical installation going unfixed, instead of being brought up to date with at least RCDs, or them going to some dodgy character a mate at the pub knows, and probably getting a far less safe job done (maybe with fake AFDD off eBay, etc, as well)

3) For a given budget, you would be better spending the extra AFDD money on a proper linked-up fire/smoke alarm. Why? Well because only around 12% of fires are due to the wiring that might be protected by the AFDD but your smoke alarm should give to a chance to escape all of them:

UK house fire statistics & common causes of fires | Morgan Clark

Updated for 2023/24, the following fire statistics have been compiled to draw attention to the risks of house fires in the UK.

www.morganclark.co.uk

This wiring was only installed 4 years ago by a professional certified company.Even though the fuse disconnected current to the appliance,I can clearly see via the 3 plug pin entries that the internal housing of the socket is blackened and it is possible that a chain of events leading to a full blown house fire was already underway before all supply to the socket wiring was isolated.As we all leave several appliances on while we are away from home ,freezer etc why isnt this standard practice?The sparkys investigation will be revealing.I will get him to check all the other sockets too as the rewiring company blamed wiring difficulties on the age and location of my house . : ) : )

Overheated plug/socket combinations can be due to either the socket, which would be your electricians responsibility, or the appliance plug, which is another issue. To me "wiring difficulties on the age and location of my house" sounds very suspicious, but without full details and someone interdependently looking at it I could not say any more.

 

[jace999]

While insisting on AFDD might seem like a good idea, in practice it is not necessarily so.

1) AFDD are not that good at stopping fires. They only add detection of an arc, and not overheating, and even the arc aspect is not that convincing (just search YouTube for John Ward doing some tests on AFDD). Also as I mentioned they do not stop fires from a simple poor connection or under-rated cable, nor would they stop fires from the likes of tuble dryers building up lint which as often classed as "electrical fires":

https://www.imperialclaimsconsultants.co.uk/faulty-whirlpool-tumble-dryer-recalls-increasing/

If they were a magic bullet to stopping fires, then why don't we see detailed analysis of what proportion of fires would be prevented?

2) They add a lot of cost. Sure that will no doubt drop in time, but today you could be looking at £2000 extra on the cost of a rewire or new CU. Now if you have paid off your mortgage and earn £50k/year that might not trouble you, but for the majority of folk that is going to make them think twice.

The unintended consequences of that are either poor electrical installation going unfixed, instead of being brought up to date with at least RCDs, or them going to some dodgy character a mate at the pub knows, and probably getting a far less safe job done (maybe with fake AFDD off eBay, etc, as well)

3) For a given budget, you would be better spending the extra AFDD money on a proper linked-up fire/smoke alarm. Why? Well because only around 12% of fires are due to the wiring that might be protected by the AFDD but your smoke alarm should give to a chance to escape all of them:

UK house fire statistics & common causes of fires | Morgan Clark

Updated for 2023/24, the following fire statistics have been compiled to draw attention to the risks of house fires in the UK.

www.morganclark.co.uk

Overheated plug/socket combinations can be due to either the socket, which would be your electricians responsibility, or the appliance plug, which is another issue. To me "wiring difficulties on the age and location of my house" sounds very suspicious, but without full details and someone interdependently looking at it I could not say any more.

Thanks.My nose went off without the fire alarms even activating.The company that did the original wiring were all industry acredited.They also cut floorboards between joists,broke a door frame by throwing a drill down in temper and the main engineer sent sat in his van for an hour before work on his phone outside our house as the boss had trackers fitted to vans but not employees boots and lefyt our home unlocked for over an hour while he went to the pub.The company changed their name a couple of years later.These types discredit the profession thats why Im not having them back and will send the socket to the NICEIC.

 

[telectrix]

for over an hour while he went to the pub.

bloody lightweight. pub visit should be at least 3 hours, 8pints, and a meat & potato pie.

 

[pc1966]

for over an hour while he went to the pub.

bloody lightweight. pub visit should be at least 3 hours, 8pints, and a meat & potato pie.

Missing presumed fed.

 

[jace999]

for over an hour while he went to the pub.

bloody lightweight. pub visit should be at least 3 hours, 8pints, and a meat & potato pi

 

[jace999]

Sparky appearing tomorrow.Meanwhile..have tried the tumbledryer which was in use at time of socket meltdown in a different socket on a different circuit.Clean pins and new fuse .It got the socket extremely hot very quicly there too before I pulled it.Apart from possibly crap sockets fitted is there any way, somehow the dryer could be pulling too much voltage through by a defect in the actual dryer or causing another issue leading to extreme heat in the socket?

 

[littlespark]

I don’t know if it was mentioned earlier, but is this a moulded on plug, or one that’s been put on?

It may be that the connections inside the plug are loose, rather than the wall socket.

 

[Avo Mk8]

It may be that the plug or its internal wiring is now damaged due to the heat it had experienced, in fact I think it likely, even if it wasn't the cause in the first place. - update - just looked at the pic of the plug - needs changing (and the cable cutting back a bit as the copper will probably be affected)

It's also possible that the appliance is taking excessive current due to a fault.
Both could be dealt with by the electrician.