Melted L and N in standard 13A plug socket

[HootsMon]

Hi folks, hope all are safe in cvd-19 world. 

I have a fitted kitchen with integrated units. The dishwasher and washing machines installed under counter on either side of the sink. Both units plug into a separate power sockets attached to the wood panel in the cupboard under the sink.  These sockets then run off the kitchen ring via a wall socket behind the rear cupboard panel (we can't access this without removing the appliance). Each appliance has its own plug from the rear of the appliance, which we manually plug into the power socket when we want to run the units. I unplug these when not in use.

In Jan 2020 I replaced the switch on the plug socket we use for the builtin dishwasher as the power on/off switch was faulty (wouldn’t turn on). The dishwasher and its power supply had never failed for 5 years since the kitchen was renovated in 2015. The circuit never tripped.

Dishwasher is a NEFF (S5443X1GB/17), 2.3-2.5kW, 230-240V, 50Hz.

The replacement plug socket I bought was a British General (BS1363-2) 800 series 13A 1-Gang SP switched 13A plug socket. 

After 3 months I now discover that the dishwasher plug socket has overheated and it stopped working (fortunately!).  My wife has started plugging the dishwasher into the power socket for the washing machine (nearby) as needed.  I notice that this power socket also heats up when we run the dishwasher - which doesn’t happen when we use the washing machine. 

When I opened the socket I replaced in Jan, I found that both the L and N wires have melted. When I installed the socket I double checked L/N/Earth wires all made a secure connection. All wires are still well attached (but L and N melted the plastic casing around the connector).

The 13A fuse is still intact.  The mains ring never tripped when the appliance runs (despite what seems like the dishwasher drawing heavy load?) I consider myself lucky that a fire didn't start!

I guess that the problem may be that I used a 800 vs 900 series plug (I see the washing machine socket is a 921 model).  With Covid we are unable to get access to qualified help as my wife is at risk.

Questions:

Is there a reason the specs for the dishwasher would require a different plug socket (given it runs hot when in use)?

If I replace the socket with a 900 series will this solve the problem?

Should I use a DP vs SP plug?

Is there any other fault that may cause the wires to melt yet not blow the 13A fuse/trip the circuit?

Many thanks for any guidance

 

[boltonsparky]

If there isn't overload loose connections is the usual cause of things melting/cables burning. Any damaged cables will need repairing properly as failure to do so will again cause high resistances and resultant heat. 

A 13a plug top fuse won't blow for a surprising amount of time if it's only just overloaded. I've seen well melted plugs with the 13a fuse still intact.

Equally your MCB will be a 32a most likely (although could be a 20a or 16a) so it would need a load of 7.36KW before being overloaded and even then tripping time would be slow. 

Any socket outlet that is genuine and rated at 13a should be ok for use up to a 13a load however some wiring accessories are of dubious quality these days, they don't make them like they used to.

What state is the plug top for the dishwasher in, is it a moulded one? 

There could be a fault within the dishwasher causing an excessive load. 

"These sockets then run off the kitchen ring via a wall socket behind the rear cupboard panel (we can't access this without removing the appliance)" this sounds suspect as a kitchen fitter masterpiece and doesn't sound right to me although I don't fully understand what you mean by it. You may have a spur off a spur so the cable is overloaded hence the melting.

 

[SPECIAL LOCATION]

I guess that the problem may be that I used a 800 vs 900 series plug (I see the washing machine socket is a 921 model).  With Covid we are unable to get access to qualified help as my wife is at risk.

Questions:

Is there a reason the specs for the dishwasher would require a different plug socket (given it runs hot when in use)?

If I replace the socket with a 900 series will this solve the problem?

Should I use a DP vs SP plug?

Is there any other fault that may cause the wires to melt yet not blow the 13A fuse/trip the circuit?

Many thanks for any guidance

With appropriate social distancing and PPE I guess you may have greater danger from electrical fault than Covid-19..

Other than manufactures product range descriptions, there is no such thing as an 800 / 900 series socket in relation to BS7671 wiring regulations..

The Socket is irrelevant if it is connected correctly.

(I have seen numerous accessories DIY'ers have connected thinking the terminations are secure and electrically sound.. But they weren't )

From my experience, a faulty pre-moulded appliance plug can cause numerous problems relating to overheating, melting and/or RCD's tripping!

(your repeated plugging/unplugging appliances may not help the integrity of the plugs terminations either)

But from what you have described I think you need the circuit double checked to verify the integrity of connections and the ring etc..

(a broken ring can also cause overheating issues..)

It is not just an excessive load needed to melt wires..

A normal load running though a poor connection will cause additional heating..

Unless you've got access to the correct test equipment, and know how to use it..

I think you either need to stop using any of those appliances until you are happy with the level of Covid risk..

Or..

Get someone who knows what they are doing to test it for you with appropriate PPE etc..

p.s.

I replaced a melted double socket on Monday due to a faulty electric kettle.... 

Guinness

 

[Geoff1946]

If I understand your description of the set up correctly the socket in question is fed from an extension to another socket, which is on the house ring and is OK.   (?)

What type and size of (presumably flexible) cable has been used?  Is it this flex which is overheating?

Even operating normally a 2,5 kw load is substantial and can cause overheating of  any plug, fuse, socket, or connection which isn't in first class condition.  Once overheating starts the "spring" of the contacts in the socket weakens and the contact there starts generating heat, and so the situation degenerates.

The odd thing to me is that both L & N overheated. One bad connection is very common, Two less so.

If you are determined to fix it yourself without expert help then replace everything which has overheated, plug, socket and if necessary cable, with good quality branded items, ensuring the "extension" cable is 1.5mm and all connections are tight.  Then keep a watch, (or feel!) on the plug when operating.  It should never feel more than very slightly warm.

 

[ProDave]

You should have an individual, properly rated socket for each appliance, with each on individually switched from a double pole isolating switch above the worktop.

It sounds like your kitchen needs some serious rewire.  Lets hope it can be done without trashing the kitchen.

Best place for appliance sockets is under the units, joust off to once side of the appliance so you can access it for testing just by removing the kick board.  the very last place you want the socket is on the wall behind the unit, particularly if they are built in.

 

[binky]

You should have an individual, properly rated socket for each appliance, with each on individually switched from a double pole isolating switch above the worktop.

that's only a requiremnt for built-in appliances, free standing units can be on a socket in under counter cupboards - locating it under sink means it is accessible. I do this all the time, as switch-fuses don't exactly look nice, and if you don't cut off moulded plug, then you don't risk invalidating any warranties.

Apart from being BG, the other possibility is that you may have clamped onto the cable insulation rather than bare copper, so not getting a decent connection. It also sounds like the molded plug may be poor?  When fitting new socket, bare the copper twice a slong as you need and fold over to double up the copper, as this will also prevent cutting through copper from over-zealous terminal tightening. 

 

[Evans Electric]

BG  socket  eh !       Perhaps not the best quality .     If the contacts that grip the plug  prongs are suspect  that could be the problem .     Socket will be OK  up to ..say.... 2K Watts  but start carping out when used at their quoted loading .     

Often happens in rewired  houses using cheapo  sockets .....they all work fine except the one for the kettle  which carries  a higher load ,,,,  typically seen with burn marks around the insert holes. 

 

[binky]

BG  socket  eh !       Perhaps not the best quality .     If the contacts that grip the plug  prongs are suspect  that could be the problem .     Socket will be OK  up to ..say.... 2K Watts  but start carping out when used at their quoted loading .     

Often happens in rewired  houses using cheapo  sockets .....they all work fine except the one for the kettle  which carries  a higher load ,,,,  typically seen with burn marks around the insert holes. 

Kitchen fitter I work with likes to buy from Screwfix who stock BG. The terminal holes are just holes, so you can insert cable end right upto plastic front plate, so it's easy to clamp onto insulation rather than your bare copper.

Dead right, the socket that supplies an appliance with a decent load is the one prone to fail after 5 years. Considering I'm still taking out 50 year old MK sockets, it shows how rubbish modern stuff is. 

 

[Evans Electric]

Yes!!!   And what did  MK  stand for  ?       Multi -Kontact  I believe .   Old MK were always the  best accessories. 

 

[binky]

Yes!!!   And what did  MK  stand for  ?       Multi -Kontact  I believe .   Old MK were always the  best accessories. 

didn't know that, learn something every day! 

Using plug-in test lead fro Zs on new sockets often fails these days, sometimes even after switching 'on-off' several times and pulling plug 'in an out ' a few times to clean contacts up. Think I'm going to take  abot more notice of that going forward, as it may be the socket is that lettuced! 

 

[HootsMon]

You may have a spur off a spur so the cable is overloaded hence the melting.

Thanks boltonsparky. It is a spur off a spur so I am concerned but the wiring is good and has held up.

Good to know that the 13A fuse and load is probably ok.

There are no loose wires. Its not a molded plug - has a 13A fused plug. 

I will change to a better quality socket and get qualified help asap to check the setup washer and the circuit etc

 

[boltonsparky]

Thanks boltonsparky. It is a spur off a spur so I am concerned but the wiring is good and has held up.

Good to know that the 13A fuse and load is probably ok.

There are no loose wires. Its not a molded plug - has a 13A fused plug. 

I will change to a better quality socket and get qualified help asap to check the setup washer and the circuit etc

The spur off a spur will need sorting as the cable can become overloaded depending what you're hanging off the end of it, that's why a spur is only allowed to feed one outlet, unless you fuse it down with a fused spur of course, then it can feed multiple outlets. 

Until you can get it sorted just make sure the spur leg/s isn't feeding more than one appliance. If it's 2.5mm cable and not running through insulation it's good for 27a but it may not be 2.5mm. There can be some right lash ups in kitchens so there's no guarantee of what cable has been used or if the original ring is still a ring. If there are any signs of heat or damaged cable it's strongly advisable not to use it at all until you can get a proper repair and test done.

As you can see below you can run 20a through a 13a fuse and it will take it indefinitely. 

 

[HootsMon]

If I understand your description of the set up correctly the socket in question is fed from an extension to another socket, which is on the house ring and is OK.   (?)

What type and size of (presumably flexible) cable has been used?  Is it this flex which is overheating?

Even operating normally a 2,5 kw load is substantial and can cause overheating of  any plug, fuse, socket, or connection which isn't in first class condition.  Once overheating starts the "spring" of the contacts in the socket weakens and the contact there starts generating heat, and so the situation degenerates.

The odd thing to me is that both L & N overheated. One bad connection is very common, Two less so.

If you are determined to fix it yourself without expert help then replace everything which has overheated, plug, socket and if necessary cable, with good quality branded items, ensuring the "extension" cable is 1.5mm and all connections are tight.  Then keep a watch, (or feel!) on the plug when operating.  It should never feel more than very slightly warm.

Thx Geoff1946. Appliance plug socket is a spur from the original wall socket/spur on the ring (which I can't see behind the rear cupboard panel). It is a standard extension lead to an unfused socket (the one that burnt out). Appliance plug is not moulded and fused 13A. Dishwasher is the only appliance for this spur. The washing machine has a similar setup (but is ok) on either side of sink. I can't see the wall socket (behind back panel) which feeds the 2 appliance spurs. Have to assume there is a single wall socket for each appliance but can't verify that yet.  

I will have to get the circuits checked out

 

[HootsMon]

Apart from being BG, the other possibility is that you may have clamped onto the cable insulation rather than bare copper, so not getting a decent connection. It also sounds like the molded plug may be poor?  When fitting new socket, bare the copper twice a slong as you need and fold over to double up the copper, as this will also prevent cutting through copper from over-zealous terminal tightening. 

You should have an individual, properly rated socket for each appliance, with each on individually switched from a double pole isolating switch above the worktop.

It sounds like your kitchen needs some serious rewire.  Lets hope it can be done without trashing the kitchen.

Best place for appliance sockets is under the units, joust off to once side of the appliance so you can access it for testing just by removing the kick board.  the very last place you want the socket is on the wall behind the unit, particularly if they are built in.

Thx binky and prodave. Appliance has the correctly rated socket (based on the dishwasher specs its 13A). Its possible I snagged the insulation but not sure why both L and N burnt out - from what I can see on the failed socket I did wire correctly (usually double the copper for safety but I'm no expert).  

As I can confirm its a spur 'extension' to unfused socket that is probably where the problem arises. as noted separately I need to get the whole arrangement checked when I can. Not using it until I can. 

 

[boltonsparky]

Thx binky and prodave. Appliance has the correctly rated socket (based on the dishwasher specs its 13A). Its possible I snagged the insulation but not sure why both L and N burnt out - from what I can see on the failed socket I did wire correctly (usually double the copper for safety but I'm no expert).  

As I can confirm its a spur 'extension' to unfused socket that is probably where the problem arises. as noted separately I need to get the whole arrangement checked when I can. Not using it until I can. 

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As suspected it's a bit of a lash up. Looks like heat from poor/loose connections, equally with flex over-tightening can damage the flex reducing its size and it's prone to getting wound up the side of the screw making a bad connection. 1.5mm flex (if it is that size) is good for 16a so you shouldn't be overloading it with just the dishwasher on there, but it's definitely not good.

Hopefully those flexes have plugs on the ends of them so they're fused down and they aren't wired directly into the hidden socket as that would be a major lash up and quite dangerous.

It wants pulling out and redoing properly, best advice would be to extend the ring (if there is still a ring) to each socket, wired in T&E not flex, and you should be problem free from then on. 

You've already said you won't be using it until it's sorted which is the best idea  

 

[binky]

love the way the live has melted into the plastic.  Think you my have got unlucky or as Bolton spark said, you have inadvertently cut through the conductors. Ideally flex should have a ferrule crimped on the end.

Buy a better make of socket, and redo with care, maybe double fold the bare copper just to make sure you don't cut through it. . Personally I would like to see that rewired to take off point in 2,5mm cable, but being a kitchen that maybe much easier said than done.