Over a month ago, I noticed the one of the switches on the double socket in the spare bedroom next door to my bedroom, had slight black scorch marks on one of the on/off switches.
When I went to turn off what was connected to it, both the switches arced loudly.
Also a FCU is wired from it to an outside 300w halogen security light. When that switch was moved, a scary sizzling noise was heard(probably arcing as well).
The upstairs power circuit circuit is protected by a 32 amp mcb and 30ma rcd.
After turning off the upstairs 32 amp mcb, I took the double socket faceplate and FCU faceplate off.
But was surpised it wasn't burnt inside, but looked like a sticky liquid of some sort had got split inside it.So cleaned it all off
All the wires were loose, most likely why it was arcing.
Strangely enough...It was an MK socket and had only been replaced about 3 years ago.
As the original socket when we moved into our house, eventually one of the switches failed on it and arced and welded the switch contacts together.
There was also wall plaster dust that had got in the FCU switch, so I cleaned that up, and made sure all the wires were TIGHT and replaced the faceplates and turned the mcb back on.
And tried out the switches and there was no arcing sounds.
Thought it was all sorted until hours later in the middle of night after using the computer I heard a very loud continous arcing sound coming from that area which really scared the living daylights out of me.
And I rushed downstairs and flipped the mcb off.
I'm very surpised big arcing(if it's arcing, not a short circuit) didn't trip the mcb or the rcd, unless they are defective.
Now I've fully disconnected the FCU(which looks pretty melted inside) and taken out the piece of cable between the double socket(the red live wire has started to overheat on it) and the FCU.
And also ordered a new FCU made by Crabtree and some high quality 2.5mm twin core and earth grey cable and earth sleeving and the suitable wire strippers/cutters and cable clips.
I'm no electrian but I did electronics years ago back in college, and read and got quite a few books on home electrical repairs.
I've already replaced the double socket with a Crabtree double socket, which has been fine for the last week. And I've installed a 10 year life optical smoke detector in the room where it happened, as it's made me rather paranoid now as the wiring upstairs is rather old.
Since the downstairs wiring and sockets and consumer unit all got replaced 15 years ago by a qualified electrian.
But the upstairs power is probably 25 years old or more, and has white shealths, not grey like the new cables.
The concerning issue is, will it occur again?
Never ever happened in my bedroom or anyone alse upstairs.
And when I connect the new FCU, I will probably need to change the 13 amp fuse in it for a 3 amp? If a 13 amp is in it.... Says it has cutout for a flex, so I presume it has a 13 amp in it.
Also I found bugs(woodlice,beetles,spiders and other insects in the old FCU) and corrosion. So moisture must be getting in from outside...
And also plaster dust.
So how do you stop plaster entering from where the mounting box is fixed by it's screws?
So how can I seal the outside hole properly against moisture?
And should the cable to the light from the FCU be changed to something like arctic cable? Incase of damage, shorts,etc...
Likely when wires were lose it overheated the units and damaged them. Once replaced should be OK.
Screws can become lose in time which is why all junction boxes have to be either a special maintenance free (spring connectors) or accessible. And the house electrics should be checked every 10 years or change of occupier which ever is sooner.
Although an electrician may not find all faults the earth loop impedance meter they use puts a fair load onto the circuits and will likely highlight most faults in trained hands.