CSI: Sparks - Drier plug melted

[Dartlec]

Called to look at a job today for a previous client. Tumble Drier giving off 'funny smell' and tripped the RCD - Called out her appliance insurance plan people, who suggested it was the fixed wiring - hence why she wanted me to have a look...

Plug and socket well and truly melted...



Clearly due to over heating or loose connection of some sort from first glance.

However, removing the socket, wiring and terminals behind showing no damage at all: Nor is there any sign of loose connection when retracting the shielding on the live pins...

It's a GET socket, so not the usual cheap and nasty ones where I've seen melting before. All the damage appears to be on the front.



And the cable feeding the socket still flexible with no sign of heat damage. (This is a single circuit 16A MCB)

The plug has a fairly obvious bulge on the top (not quite so clear in the pictures)



as well as the obvious damage around the fuse carrier/live pin...



So my view is that the problem was in the moulded plug on the appliance which then caused the socket damage, either due to prolonged over heating, or some fault within it - or the drier is now running above it's rated 2800W and over time has caused the plug to over heat and melt....

The drier is a relatively old AEG, which has been repaired a few times before...

The appliance people wanted to just put a new socket and plug on, but I'm of the view that they should be checking a bit further to see what the fault is before declaring it safe.

Client would like them to write it off and get a new one since she's worried (rightly) about fire risk. I'm going to put a site report together stating that the fixed wiring was not at fault and that the issue was clearly with the appliance and that it should be tested and declared safe by an approved appliance engineer before being reused...

I PAT tested the appliance, and it passed, at least under the new code, with a 0.93 mA leakage but IR fine and earth loop still intact...

Anyone like to add their experience or wisdom?

Cable to the appliance still seemed fine with no heat damage. If I was reconnecting this myself, I'd be tempted to run it from an appliance outlet plate since it's on a 16A MCB, but the drier does state requirements for 13A fuse (although in this case it doesn't appear to have gone)

Drier was under a worktop if that matters - Circuit is a single radial from 16A MCB to an outlet plate, where 1.5mm flex feeds the single socket shown...

 

[GBDamo]

Just a guess but could there be sufficient tracking via the carbonised deposits, would it be deposited as graphite?

Carbon is not conductive but graphite is.

 

[SparkySy]

I hate sealed plugs like that, no way of inspecting them apart from what you can see on the outside! I've seen a few like that, usually found it to be the holders for the fuse are weak and don't hold it properly causing it to get very warm!
Had one I cut in half with the bandsaw and found it was the actual connection from the live pin to the fuse holder at fault.
Also had one on a Bosch dishwasher that had been so tight behind it that it had managed to melt itself into the insulation in the back of the dishwasher and the socket, as I pulled the appliance out the plug stayed attached to the insulation and left the live pin in the socket!

 

[Dustydazzler]

What’s the skinny white flex poking out the bottom of the socket in pic #1

 

[timhoward]

So my view is that the problem was in the moulded plug on the appliance which then caused the socket damage, either due to prolonged over heating, or some fault within it - or the drier is now running above it's rated 2800W and over time has caused the plug to over heat and melt....

Agree. I wonder if putting a new plug on and running the drier with a clamp meter at the MCB would give some reassurance about the drier itself.

 

[Dustydazzler]

Almost certainly a faulty plug top , as above cut off , replace …

 

[westward10]

That looks like some kind of liquid damage you can see in running down the wall. The plug would have appeared to "pool" this liquid between its face and the socket outlet which has caused arcing and overheating.

 

[Dartlec]

What’s the skinny white flex poking out the bottom of the socket in pic #1

That's the feed to the socket - only 1.5mm running from the original socket point which is now to the right behind the unit...

16A radial so no real issue with it electrically, and no sign of heat damage to it...

 

[SparkySy]

@westward10
You can see something down the wall but I would expect to see it on the top part of the socket face as well if that was the cause?

 

[Dartlec]

That looks like some kind of liquid damage you can see in running down the wall. The plug would have appeared to "pool" this liquid between its face and the socket outlet which has caused arcing and overheating.

I see what you mean - though I think that's just a crack in the wall and the angle of picture makes it appear to line up.... There's a sink to the right of it, but worktop is properly sealed so not sure it's water damage...

 

[westward10]

@westward10
You can see something down the wall but I would expect to see it on the top part of the socket face as well if that was the cause?

To me the plug top and socket face indicate a pooling of liquid between them. It could have dripped to to top of the plug then down the wall. It just doesn't look like a sole electrical failure.

 

[westward10]

I see what you mean - though I think that's just a crack in the wall and the angle of picture makes it appear to line up.... There's a sink to the right of it, but worktop is properly sealed so not sure it's water damage...

Yes I can also see it could be an optical illusion but I still believe that is a liquid ingression issue.

 

[SparkySy]

I do agree that it does look like something has pooled between the plug and socket but I think it is more thermal damage that has caused it than a liquid as @Dartlec says the worktop is well sealed. There doesn't seem to be any residue on the bottom of the socket or flex either as you would expect with spilt liquid.

 

[Dartlec]

I didn't notice any liquid mess while looking at it, though my eyes are probably worse than most. The smell was awful still though!

 

[SparkySy]

I think the stain on the bottom right is from the plug itself as it's been happily melting away.

 

[DPG]

I'd put money on it being down to the plug, and highly likely the fuse contacts within it.

 

[Pete999]

I'd put money on it being down to the plug, and highly likely the fuse contacts within it.

Agree, or a dodgy connection in the socket, more likely to be in the plug though, worth checking both

 

[UNG]

I've never liked moulded plugs on high current appliances as you can't check the quality of the connections inside the plug.
When moulded plugs first hit the market an NHS HTM banned them from NHS premises due to poor quality manufacture, there where a number of reports of stray strands of cable visible in the outer casing

 

[Lucien Nunes]

Looks like a bog standard high resistance fuse clip, not sure why people are trying to make it more complicated. Happens all the time.

I've never liked moulded plugs on high current appliances as you can't check the quality of the connections inside the plug.

But a spot-welded connection is the best and most maintenance-free connection you can get. If properly made it will carry the cable's rated current for the life of the product with no local heat generation. A screw terminal will never make a connection that is as reliable and of such low resistance. Of course if it is a dodgy cordset then all bets are off, not just on the connections, but you can spot most of them from the outside.

Personally I'm much more interested in the integrity of the fuse clips. A plug with good clips trumps one with weak clips, regardless of the method of attachment of the flex.

 

[UNG]

Looks like a bog standard high resistance fuse clip, not sure why people are trying to make it more complicated. Happens all the time.

Which is possibly down to....... a poor spot weld!

But a spot-welded connection is the best and most maintenance-free connection you can get. If properly made it will carry the cable's rated current for the life of the product with no local heat generation. A screw terminal will never make a connection that is as reliable and of such low resistance. Of course if it is a dodgy cordset then all bets are off, not just on the connections, but you can spot most of them from the outside.

As with a lot of things built to a price is it "properly made" there are probably tens if not hundreds of thousands of these cordsets manufactured everyday with a 1 in ??? production batch test rate other than a visual inspection of the outer shell on site what else can you check when it is encased in plastic. This is one plug in many thousands that has failed so the fail rate is likely to be within an acceptable norm although that isn't much comfort for the person whose house suffers fire damage

Personally I'm much more interested in the integrity of the fuse clips. A plug with good clips trumps one with weak clips, regardless of the method of attachment of the flex.

I've seen a good number of failed moulded plugs in the last 30 - 40 years and the fuse clip has clearly not been the only failure point, although with some failures the manufacture quality of the socket may have been a contributing factor

 

[Lucien Nunes]

One can usually tell whether the heat has originated at the pin/socket contact, the fuse contact or the flex terminal. Unless the plug is corroded, dirty or is not of correct manufacture, any heating at the pin/socket contact is invariably the fault of the socket because that determines the contact pressure. Any heating at the screw terminal is invariably the fault of the whoever wired it.

Sometimes heating at one point causes oxidation and loss of contact spring temper at another, creating a domino failure. An overheated fuse contact can heat the line pin and cause the socket contact to fail, or vice versa. It is not always obvious which is the original culprit, but there is an ever-present source of heat in the fuse element that works quietly behind the scenes to accelerate the age-related rise in resistance at its end-caps and set the whole process off.

Regarding the inspection of overmoulded cable terminations, I don't see that it's any different to any of the other hidden connections in the circuit. You can't inspect the spot-welds in the MCB or the rivets holding the current-carrying parts of the socket together, nor some of the ones in the appliance. The sealed casing of the dryer's cheap little heater relay hides two riveted and two spot-welded connections carrying the same current that destroyed the plug, with the aggravating factors of the contact heat dissipation and movement to show up any weakness.

Sure, fake and unapproved cordsets can be quite horrendous and deserve their reputation, but the captive cable and plug fitted to a brand-name appliance is not likely to be one of those so we can largely exclude that sector of the failure pie-chart from the present discussion.