Advice on Burnt out wall socket

Alex Woodall · Friday at 6:06 PM

Hi All

Wonder if someone can give me a little advice on a burnt out socket I’ve found today:

[ElectriciansForums.net] Advice on Burnt out wall socket

Socket has now been isolated at the fuse board and is on a small ring with only 2 other sockets and a 30amp rcd.

Items plugged into the socket were a tp-link smart plug, with a lamp connected to it, and a 4 way extension lead with an Amazon firestick and a wireless router bridge connected. So nothing pulling significant loads.

Socket was installed about 10 years ago and there haven’t been any issues, that I know about, since then. We’ve recently had an extension built which involved replacement the fuse board (new FuseBox model).

Whilst I suspect it most likely that the issue was the live connection in the outlet, which is what has burnt, it feels like potentially too much of a co-incidence that this has happened just a few weeks after the fuse board was changed having been fine for 10 years.

Could the new fuse board have caused something to change here which has resulted in the socket burning out?

Thanks in advance for any assistance

Alex

littlespark · Friday at 7:17 PM

whatever was plugged in there will be damaged as well....

Coincidence... unless they removed that socket for some reason when they changed the board.
Its been a loose cable, and the heat caused by arccing.

You said it wasnt a big load... so im surprised its caused that much heat.

Im surprised you didnt smell it.

The back box appears to be only a 25mm deep one... A lot of decorative metal sockets ask for a 32mm.... maybe the live cables were close to the back wall of the box?

Did you mean a 32A, 30mA RCBO? or a 32A MCB with an upfront RCD mainswitch? (photo?)

Its a simple enough fix, but maybe beyond a DIYer.

Avo Mk8 · Friday at 7:20 PM

Alex Woodall said:
Socket was installed about 10 years ago and there haven’t been any issues, that I know about, since then. We’ve recently had an extension built which involved replacement the fuse board (new FuseBox model).

Whilst I suspect it most likely that the issue was the live connection in the outlet, which is what has burnt, it feels like potentially too much of a co-incidence that this has happened just a few weeks after the fuse board was changed having been fine for 10 years.

Could the new fuse board have caused something to change here which has resulted in the socket burning out?

Littlespark has said it all before I finished, but I'll post anyway - these were my thoughts:

Has the advent of the extension resulted in additional loads being used on this particular circuit?
Or, for example, have you been using electric heater(s) on this circuit since it's got colder recently?

The socket is on a ring circuit, so a current of up to 10 or more Amps could be trying to flow through the connection between those two (burnt) brown wires (irrespective of whatever is plugged into that socket). The (L) screw terminal in the socket is responsible for maintaining a good connection between the brown wires, and quite clearly it hasn't done the job well, probably not having been tightened to the required torque in the first place.

This fault should have ben identified during the fuseboard change, if it was present at that time.
Have you got documentation from that work that gives figures for the ring circuits?

Alex Woodall · Friday at 7:29 PM

littlespark said:
whatever was plugged in there will be damaged as well....

Coincidence... unless they removed that socket for some reason when they changed the board.
Its been a loose cable, and the heat caused by arccing.

You said it wasnt a big load... so im surprised its caused that much heat.

Im surprised you didnt smell it.

The back box appears to be only a 25mm deep one... A lot of decorative metal sockets ask for a 32mm.... maybe the live cables were close to the back wall of the box?

Did you mean a 32A, 30mA RCBO? or a 32A MCB with an upfront RCD mainswitch? (photo?)

Its a simple enough fix, but maybe beyond a DIYer.

Excellent thanks and definitely did smell the burning and that’s what directed me to this socket - perplexed as to why the fuse in the consumer unit didn’t trip though?

Builders didn’t touch anything in this room, unless they potentially took this socket out as part of the NIC testing, so must just be coincidence.

I didn’t think it was likely to be anything fuse board related but so strange that nothing for 10 years and then this happens 6 weeks after the fuse board is changed though!

Photos of fuse board attached

Alex Woodall · Friday at 7:36 PM

Avo Mk8 said:
Littlespark has said it all before I finished, but I'll post anyway - these were my thoughts:

Has the advent of the extension resulted in additional loads being used on this particular circuit?
Or, for example, have you been using electric heater(s) on this circuit since it's got colder recently?

The socket is on a ring circuit, so a current of up to 30-odd Amps could be trying to flow through the connection between those two (burnt) brown wires (irrespective of whatever is plugged into that socket). The (L) screw terminal in the socket is responsible for maintaining a good connection between the brown wires, and quite clearly it hasn't done the job well, probably not having been tightened to the required torque in the first place.

This fault should have ben identified during the fuseboard change, if it was present at that time.
Have you got documentation from that work that gives figures for the ring circuits?

Thanks and very much appreciated

Loads on this circuit unchanged - it’s 3 double sockets that serve the media/av setup (sky box, led tv av receiver, router, and a couple of lamps). If anything it’s reduced as we haven’t got a fan connected to it anymore.

Haven’t had the NICEIC cert through yet - have chased up.

I would have thought something like this would have caused the RCD to trip though?

Avo Mk8 · Friday at 8:00 PM

Alex Woodall said:
perplexed as to why the fuse in the consumer unit didn’t trip though?

There's no excess current flowing, just your normal (fairly light) loads. A high resistance joint has developed in a wire feeding the various items round the ring, so some watts of energy (heat) are generated, and this tends to be a runaway situation - heat increases the resistance which generates more heat etc. until something gives!
An RCD won't trip until there is an imbalance of current in L and N, and there's nothing here to create that imbalance unless a stray burnt wire develops a leakage to earth, which doesn't appear to have happened, or touches the metalwork, which would trip the MCB as well! (Or as Mainline has mentioned below - RCBO in your case!)
This sort of scenario is what the arc fault detection devices (AFDD's) were aiming to tackle, that are now mandated in various situations, but which don't seem to be attractive to many.

mainline · Friday at 8:17 PM

Alex Woodall said:
Excellent thanks and definitely did smell the burning and that’s what directed me to this socket - perplexed as to why the fuse in the consumer unit didn’t trip though?

Builders didn’t touch anything in this room, unless they potentially took this socket out as part of the NIC testing, so must just be coincidence.

I didn’t think it was likely to be anything fuse board related but so strange that nothing for 10 years and then this happens 6 weeks after the fuse board is changed though!

Photos of fuse board attached

View attachment 118630
View attachment 118631

If it's the one that is switched off saying lounge sockets it's a 20amp rcbo so maybe not a ring final unless it's been downgraded for some reason.

Alex Woodall · Monday at 12:53 PM

Avo Mk8 said:
There's no excess current flowing, just your normal (fairly light) loads. A high resistance joint has developed in a wire feeding the various items round the ring, so some watts of energy (heat) are generated, and this tends to be a runaway situation - heat increases the resistance which generates more heat etc. until something gives!
An RCD won't trip until there is an imbalance of current in L and N, and there's nothing here to create that imbalance unless a stray burnt wire develops a leakage to earth, which doesn't appear to have happened, or touches the metalwork, which would trip the MCB as well! (Or as Mainline has mentioned below - RCBO in your case!)
This sort of scenario is what the arc fault detection devices (AFDD's) were aiming to tackle, that are now mandated in various situations, but which don't seem to be attractive to many.

Hi Both

Many thanks for your feedback on Friday - much appreciated.

Electrician came out on Saturday morning and replaced the socket so all is now repaired.

I've also now received the EICR cert and all was seemingly good on the day the test was done (photos attached) which is even more strange.

It doesn't look like this is a ring main circuit (as mainline correctly spotted) which I assume is why these sockets have two live and two neutral wires to each terminal - would this setup make these sockets more susceptible to an arc fault?

Have been looking at AFDDs and can fit them (combined AFDD and RCBOs) on all the socket circuits in the house for circa £600, which seems a small price to pay to ensure that this fault didn't become more serious. However from what i can understand and AFDD wouldn't have picked this particular issue up as it occurred in series not parallel, which to be fair does seem like quite a blind stop for a £100 circuit breaker...

Am now also considering getting another EICR carried out and testing every socket in the house - would a multi meter be able to detect loose connections or will every socket have to be removed from the wall (i'm conscious that a couple are in very difficult to access locations?

PS Electrics · Monday at 8:43 PM

Alex Woodall said:
Hi Both

Many thanks for your feedback on Friday - much appreciated.

Electrician came out on Saturday morning and replaced the socket so all is now repaired.

I've also now received the EICR cert and all was seemingly good on the day the test was done (photos attached) which is even more strange.

Just catching up on this.

If the sequence was you had an EICR which recommended a board change is there a chance the socket was disturbed during the EICR? The possibility increases if you say the other sockets are less accessible.

Of course it would be impossible to know for sure.

An EICR is a snap shot much like an MOT because the car passes on Monday doesn't necessarily say it would pass a week later.

Would be interesting to see the test results from the EIC of the board change to compare with the EICR. Again nothing would be conclusive but there is a chance because the circuits were tested say a week earlier they may or may not of used those results on the EIC? Assuming the same company did both the EICR and the Board change.

Alex Woodall said:
It doesn't look like this is a ring main circuit (as mainline correctly spotted) which I assume is why these sockets have two live and two neutral wires to each terminal - would this setup make these sockets more susceptible to an arc fault?

Have been looking at AFDDs and can fit them (combined AFDD and RCBOs) on all the socket circuits in the house for circa £600, which seems a small price to pay to ensure that this fault didn't become more serious. However from what i can understand and AFDD wouldn't have picked this particular issue up as it occurred in series not parallel, which to be fair does seem like quite a blind stop for a £100 circuit breaker...

It is my understanding they will work with both series and parallel arc faults but watching David Saverys videos on these especially the Hager brand doesn't instill confidence.

mainline · Monday at 8:55 PM

It could be that the builders used that outlet for something like a cement mixer ?

It would have needed a fairly substantial load to cause that.

Alex Woodall · Monday at 10:15 PM

PS Electrics said:
Just catching up on this.

If the sequence was you had an EICR which recommended a board change is there a chance the socket was disturbed during the EICR? The possibility increases if you say the other sockets are less accessible.

Of course it would be impossible to know for sure.

An EICR is a snap shot much like an MOT because the car passes on Monday doesn't necessarily say it would pass a week later.

Would be interesting to see the test results from the EIC of the board change to compare with the EICR. Again nothing would be conclusive but there is a chance because the circuits were tested say a week earlier they may or may not of used those results on the EIC? Assuming the same company did both the EICR and the Board change.

It is my understanding they will work with both series and parallel arc faults but watching David Saverys videos on these especially the Hager brand doesn't instill confidence.

Hi and thanks

To answer queries:

1) Board change was at my request as the extra circuits required, inc for an A/C unit, required a secondary fuse board under the stairs so made sense to replace with one big enough for all new circuits and leaving expansion for EV charging etc in the future.

2) Therefore new board was installed first and then EICR done once all works complete. I don’t think an EIC was done on the old board before removing as plan was always to change.

3) Socket definitely not disturbed during testing as the decorators caulk around the edge was undisturbed until I removed the socket.

4) inaccessible sockets are behind a wardrobe upstairs and on the 1st floor sockets ring final

5) I did move a lamp, on a Tp-link smart plug to this socket in between testing and the socket burning out - perhaps just very unlucky that plugging something new into this socket disturbed a partly loose connection?

Alex Woodall · Monday at 10:20 PM

mainline said:
It could be that the builders used that outlet for something like a cement mixer ?

It would have needed a fairly substantial load to cause that.

Afraid not - this room is at the front of the house where no works were done.

Only items plugged into this socket were a tplink smart plug with floor lamp connected, a four way extension cable with an Amazon fire stick and a deco m5 mesh router.

The radial circuit has two other sockets on it which had 1 table lamp, a 55” led tv, sky q box, a denon av receiver and a Panasonic surround sound subwoofer.

So nothing particularly load intense - worth getting some PAT testing done on those appliances?

PS Electrics · Monday at 10:32 PM

Alex Woodall said:
Hi and thanks

To answer queries:

1) Board change was at my request as the extra circuits required, inc for an A/C unit, required a secondary fuse board under the stairs so made sense to replace with one big enough for all new circuits and leaving expansion for EV charging etc in the future.

2) Therefore new board was installed first and then EICR done once all works complete. I don’t think an EIC was done on the old board before removing as plan was always to change.

3) Socket definitely not disturbed during testing as the decorators caulk around the edge was undisturbed until I removed the socket.

4) inaccessible sockets are behind a wardrobe upstairs and on the 1st floor sockets ring final

5) I did move a lamp, on a Tp-link smart plug to this socket in between testing and the socket burning out - perhaps just very unlucky that plugging something new into this socket disturbed a partly loose connection?

Ok Thanks for taking the time clearing all that up.

mainline · Tuesday at 8:19 AM

Alex Woodall said:
Afraid not - this room is at the front of the house where no works were done.

Only items plugged into this socket were a tplink smart plug with floor lamp connected, a four way extension cable with an Amazon fire stick and a deco m5 mesh router.

The radial circuit has two other sockets on it which had 1 table lamp, a 55” led tv, sky q box, a denon av receiver and a Panasonic surround sound subwoofer.

So nothing particularly load intense - worth getting some PAT testing done on those appliances?

I don’t think a pat test is going to be very helpful.
Could it have had any substantial loads prior to what’s on it now such as a heater or dehumidifier.
This outlet isn’t end of line so I would have expected to see some intermittent failure of the other outlets.
Anyway I’m sure it will be fine now that the connections have been sorted.

Advice on Burnt out wall socket

Alex Woodall

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littlespark

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Avo Mk8

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Alex Woodall

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Alex Woodall

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Avo Mk8

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mainline

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PS Electrics

mainline

Alex Woodall

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Alex Woodall

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