Electric Socket Went Bang - help on fixing please

ThisIsWeird

What are you minded to do, DIY76?
I hope it's to get a sparkie in as, from your description, there is something strange going on regarding the oven circuit - this is not a straight-forward case of the ext lead plug had a short, arced in a dramatic way, and tripped the MCB. 
The fact the oven circuit remains off is not good in any context, even if the cause is easily found - like a loose connection in that damaged socket - because it implies a 'spurred' oven connection. For such a potentially high load device, that is surely not ideal?
Have you opened the ext lead plug yet, to check the cause? I'd certainly do that as you should want to know what made this happen. And that might also be a bit of a mystery as the wires seem to have arced and 'blown' quite spectacularly but the fuse and MCB didn't quite fast enough. But since we are talking tiny fractions of a second, I guess quite possible.
If the ext lead is a decent one and otherwise in good condition, there is no reason to junk it - it 'should' just require a new plug fitted after all the affected wire ends are trimmed off - but I'd suggest you need to be 100% certain of the cause before you entertain this.

Anyhoo, there is more amiss here than at first glance, '76, so please get a sparky or a truly knowledgeable colleague to check it out, and you need them to be able to say, "Ah, I see - this is what happened, and this is what's now going on..."

DIYhelp76

Hi everyone,

Thanks very much for all the helpful replies, especially "This is Weird".  Sorry for long silence but very busy working week. I'm going to post some photos below which hopefully can  help clarify.  We are capable of wiring plugs and sockets and have done this before.  Would not touch cabling as not qualified for this. But if we can fix this ourselves safely, we would prefer to do so. Or at least to ID where the issue is and how bad it might be.

Have left the main electrics on all week with no issues.  Though obviously oven and other socket still unoperational.

I think the root cause was 99% the faulty extension lead. The cable was virtually severed near the plug end (wear and tear). I feel stupid as I should have been checking and noticed this, but it was one of those ones which is integral to an ironing board and just gets plugged in every now and again and folded in between - probably led to the damage). Lesson learned!

The oven does not appear to be on its own circuit as far as I can work out.  At the fuseboard there are only 6 switches - one double one for isolating all electrics, then 5 other switches which are variously labelled with "sockets down", "lighting up" etc.

There are various other sockets dotted about the kitchen. These all work.  So, my uneducated guess is that this oven socket and the damaged one are linked together.  I would like to think(!) that the last owners installed the socket for the oven and then maybe ran a spur off of this for the (damaged) double socket next to it and that this is as far as that "run" of cabling goes.  But it's just a guess. My further guess is that maybe the fuse at the fused oven switch was blown by the extension lead explosion and that if that fuse and the damaged socket are replaced things might work again.  But I'm worried if the length of cabling buried in the wall between these switches could have been damaged as well? I don't know how to test for this.

Yes, the oven is a single oven, plug in type of the lower rating.  When replacing this, that's all we could put in due to the fact there isn't a separate higher powered socket at the fuseboard.

I know I'm not probably using all the correct terminology, but hope my explanations and the photos clarify any misunderstandings.  Yes, I did mean "tripped" at the consumer unit/fuseboard.

Would it be a safe thing to try now to change the fuse at the fused oven switch?  I can see the screwdriver slot for opening this.  Excuse dimness, but will this just be a plug size/type of fuse or do I need to buy something else more specialised?  Obviously I will switch off all mains electrics before tackling this.

Would like to try to work on this in the next few days, so very grateful for any further help.  

Will try to upload the photos now.

DIYhelp76

Photos are below 

CSI_Yorkshire

I think you would be safe to change the fuse, and yes it will be a "plug size" one.

ThisIsWeird

Hi DIY76.

The cause of the 'bang' is no surprise, so at least that part of the mystery is taken care of. Also, there is no real reason why that plug cannot be reused on that same cable once you've cut off a couple of inches beyond the offending shorted end. Give the plug a good clean, of course, and check the fuse.

Confirm - is this a separate extension cable, or an original part of the ironing board setup? For the former, you should ensure the actual cable is adequate for 13A loads, check the fuse, and replace if necessary. From 'visual', the cable would appear hefty enough (oops - Risteard has blown a meta-fuse!). For the latter - if it's actually part of the iron's setup, so presumably in the region of 2kW load - then 13A for def. Either way, it'll be interesting to see if that fuse blew as well as the MCB being tripped.

Ok, the sockets. A few scenarios here, some good, some not so. In essence, the oven FSU should work fully independently of the Affected Double Socket - the 'ADS' from now on... Ie, the FSU fuse (that'll be 13A too, and identical to the one in the plug top, so feel free to replace - power off at the CU, of course) should not have blown due to the ADS, and should only be protecting the oven itself. However, it may have been wired differently to include both items (oven and ADS) being protected by that fuse, either intentionally or thro' ignorance. It shouldn't be - a 13A fuse (the largest that'll fit in the FSU) should not be asked to handle the ~2kW of the iron and the ~2+kW of the oven at the same time; almost certainly it would blow if both used simultaneously.

Since you claim to be competent enough to swap sockets, then by all means carry out some basic checks.

1) First, as you said, replace the FSU's fuse. Power off. Prise holder out. Swap with 13A fuse. Do you have a continuity tester to check whether fuses are ok? Does the oven now work? Does the ADS socket now work? (If so, we have weird wiring...)

2) Undo both the FSU and ADS, pull them out gently, and have a good close look at what's going on behind them. Check for the number of cables going to both ends of the FSU, 'IN' & 'LOAD'. Check for any signs of 'arcing' - any sootiness as you have on the plug...? Any signs of melted insulation at their ends? Any excess of bare wire showing from the terminals that could hint at it not being secured fully? Take some photos to show where the wires are going, and how they exit the back box - possibly in three different directions from the FSU's - and post them on here, please. They must show the ID of the terminals.

Give each wire a gentle tug (the CU is off, yes?) Give each terminal screw a gentle tighten - they should require some force to do up any further.

Report back.

DIYhelp76

Hi This is Weird, 

Just a quick "thank you" for now for all your time and common sense advice.  I need a bit of time in the next few days to set aside for this, to buy a new double socket, replacement fuse etc and have the time to be able to switch off all electrics.

Re the ironing board, the extension cable is a whole piece which was just attached to the underside of the ironing board.  It slides into a holder under the board.  I would then plug the iron into the extension socket bit which sits under the board.  I assume it came with the ironing board originally as we didn't add it. I will try putting another plug and fuse on the original extension lead to re-use, but if not it's not the end of the world as I can just plug iron directly into wall socket (when it's working again   

So, just wanted to say thanks for now. I will follow your suggestions and report back with more photos of what I find...eek!

littleboo

The state of the flex where it enters the plug is frightening - that didn't happen overnight

ThisIsWeird

littleboo said:

The state of the flex where it enters the plug is frightening - that didn't happen overnight

I'm guessing that DIY76 has learnt their lesson, and their washing machine has been put to considerable use.

chris_n

It is very likely that socket is run as a spur from the fused side of the oven switched fuse. Otherwise there should have been no circuit to blow the fuse.

DIYhelp76

Hi ThisIsWeird and all,

Sorry for the delay, but I've now made a bit more further progress.  Oven now working!  Well, power anyway, yet to actually test it...

Both 13Amp fuses in the extension lead and in the fused spur unit (FSU) for the oven had blown.  I replaced the fuse for the oven.

I have wired in a new socket for the Affected Double Socket (ADS). Will paste some photos below to show the existing wiring I found when I did this.  I could see no soot damage or any signs of melt on the wire insulation.  The old socket itself could not be switched on or off, so although it looked undamaged when I removed it, something must have been damaged on its insides.  Will dispose of it. 

As the new fuse has lead to the oven power being restored, I did not open up the oven fused socket, but hope it is okay, going by the condition of the ADS which showed no damage inside. 

Just a few other questions please, if I may.  The old ADS I removed had the L and N ports the other way around to the replacement socket I wired in.  So I needed to swap the direction of the wires in the wall.  One of the blacks (neutral) was a bit short, but I just managed to make it reach the port on the (now) opposite side, and it seems securely screwed in.  However, to be on the safe side, before I plug anything into the newly wired socket, I would like to buy one of those plug in socket testers.  Am I right, that this will be a risk-free way to test (a) I've wired it in correctly and nothing is loose and (b) there are no other problems with the wiring?  I'd like to do this before plugging any actual equipment into it.  Maybe as a double safeguard, I should switch off the FSU for the oven before testing this newly wired ADS? 

I have a feeling (but don't know) that maybe all of the kitchen sockets (including the oven with its FSU) are on one "circuit".  There are only five "switches" at the consumer unit, these read: Shower, Down Lights, Up Lights, Up Sockets and Down Sockets.  There definitely isn't a separate one for the oven which people seem to be suggesting should be the case.  This is an Edwardian house. It has all the old black and red wiring (which we only know from changing the sockets to metal ones when we moved in).  We've been here 10 plus years and haven't renewed the wiring.  Unless this existing set up is very dangerous we would not like to renew wiring now as we may move.  ThisIsWeird, I noted what you said about restricting what is being used at the same time as the oven, so we can do this going forward. 

If existing set up is very dangerous and we should install a separate circuit for the oven, what would this involve, cost-wise and upheaval-wise?  The walls in the kitchen are tiled and the consumer unit is a long way away in the carpeted hallway (ceiling area).  I guess this will involve digging holes in walls and possibly disturbing kitchen tiling etc? And maybe a new consumer unit as there appear to be no more "switches" available there for another circuit breaker.

There may be worse...  When re-wiring the ADS, I noticed three "incoming" cables (visible in the photo).  Two come from the top down.  One comes the bottom left in, looking like it's coming through the wall.  Looking behind this ADS to see where this cable might come from, there is wall which is shared with an external wall where there used to be an outside toilet (no longer in use - used as garden storage).  In that outside loo is a removed brick in the wall with a cable running out of what looks suspiciously like the same location as the ADS, which powers an outside power socket on the wall in the garden (used for garden mower).  I am now not sure whether this is "okay"/safe, if it is being run from that same socket.

Any further advice gratefully received.  Thanks very, very much for all the help provided to date.