When electrics go wrong!!!

[crr003]

May I add this one (I had the offending sink waste disposal replaced by a plumber but I kept the old one).

There was a big bang and a breaker tripped. The tenant found this blackened socket. Where did all this black deposit come from? The molded plug looks undamaged - the 13A fuse was fine - can anyone explain what physically blew up here? I'm just interested.
I plugged the unit into an extension cable in the back garden and it blew the fuse in the extension cable (and left the same black deposit). The disposal was free to rotate so I don't know where the problem was.

 

[LukeD]

Opening an external lighting joint box.

Funny thing...last week fitting some security gear outside .The lady enquired why i was drilling 2 tin holes into each connection box etc. I know many guys that wont bother ...madness . few seconds can save a lot of issues

 

[littlespark]

May I add this one (I had the offending sink waste disposal replaced by a plumber but I kept the old one).

View attachment 97391

There was a big bang and a breaker tripped. The tenant found this blackened socket. Where did all this black deposit come from? The molded plug looks undamaged - the 13A fuse was fine - can anyone explain what physically blew up here? I'm just interested.
I plugged the unit into an extension cable in the back garden and it blew the fuse in the extension cable (and left the same black deposit). The disposal was free to rotate so I don't know where the problem was.

Classic dead short between live-neutral or live-earth. The fault is nothing to do with the motor, so its spinning freely.

The black deposit is powdered charred metal. If you can visually inspect the plug pins with a good plug, youll see damage on the pins. The metal has laterally exploded into powder. If not the pins, then the socket youre plugging into.

Best place for that appliance now is the council dump.

 

[crr003]

Classic dead short between live-neutral or live-earth. The fault is nothing to do with the motor, so its spinning freely.

The black deposit is powdered charred metal. If you can visually inspect the plug pins with a good plug, youll see damage on the pins. The metal has laterally exploded into powder. If not the pins, then the socket youre plugging into.

Best place for that appliance now is the council dump.

Thanks for replying.

I had a look at the plug pins before I threw it all out - they looked ok which confused me (easily done...). I was hoping to see the black insulation that covers about half of the pin vaporised, but it looked OK. Although the 13A fuse was intact (electrically/physically), the "live end" connector in the plug that holds the fuse was much blacker than the other end. I thought the fuse should have protected something, but it looks like the short was somehow before the fuse. The disposal had been working OK for about 8 years and then "bang"!

 

[Simon47]

My guess would be that a build up of dirt and damp eventually created a track which allowed an arc to form. Normally the distance is such that even when there's lightning induces surges about, you won't get arcing between L & N. But add dirt and moisture, and perhaps something sub-standard in manufacture, and you can get arcing. Once an arc forms, then the ionised air is a good conductor and the arc won't go out until either the power is cut off (the upstream fuse/breaker goes) or the arc is manipulated in such a manner that it gets broken. The energy in the arc can be "a surprising amount", and in all that black there is likely to be as least some it conductive material - so I'd be replacing the socket as well because it definitely doesn't have the arc resistance that it once had.

 

[crr003]

My guess would be that a build up of dirt and damp eventually created a track which allowed an arc to form. Normally the distance is such that even when there's lightning induces surges about, you won't get arcing between L & N. But add dirt and moisture, and perhaps something sub-standard in manufacture, and you can get arcing. Once an arc forms, then the ionised air is a good conductor and the arc won't go out until either the power is cut off (the upstream fuse/breaker goes) or the arc is manipulated in such a manner that it gets broken. The energy in the arc can be "a surprising amount", and in all that black there is likely to be as least some it conductive material - so I'd be replacing the socket as well because it definitely doesn't have the arc resistance that it once had.

Thanks.
The socket is under a sink and although there was no sign of damp/leaks it could have got wet. I'm annoyed I didn't measure L-E resistance etc. of the disposal when I had the chance.
Here's another picture of the extension block I plugged the disposal in to see what would happen - note the burned groove to the left of the N hole and the edge of the extension is burned off and there's a nice image of where the fuse holder fits! (Fuse didn't blow). Powerful stuff.

 

[brianmoooore]

Looks like the tracking was from the neutral pin to the fuse holder on the face of the moulded plug.

 

[Biff61]

here's the result of a numpty damaging a brand new voltage stabilizer by getting the 3 phase connections on a generator wrong, and its all marked R,S,T,N. Connected a phase output line to the neutral and neutral to a pahse so it put two phases through the master rotavolt controller and left the incoming utility switched on while testing the changeover. By the time a replacement is shipped from UK looking at around 5K. Also took out the 400amp Auto changeover switch, another 3k to replace. Lucky not to lose the generator as well as it shut down within about 5 seconds of power being turned on. Thankfully the main switch in the MDB was off it could have run in to hundreds of thousands to repalce printers, photocopiers, and the data centre.
Lets just say he's not working for us anymore and will not be getting references.

 

[Electro-tech]

Thought I would share this burnt-out Inverter that I discovered. The customer wondered why it had stopped generating!
This was caused by water ingress & water pooling in the bottom causing a short between the grid connection 3 phases & which must have short-circuited the DC MC4 input before finally giving up. Good ole Samil Inverter 17kw 3 phase, no wonder they went bust. (Chinese) . I think I am going to give Rayliegh Instruments a try from CEF, I would prefer Fronious but there is a back order, due in sept maybe.

 

[Doomed]

 

[nicebutdim]

View attachment 110203

Must have taken considerably more effort than configuring correctly.

 

[Mike Johnson]

Must have taken considerably more effort than configuring correctly.

They must have thought about it for along time, I wonder if they ever tried to power it up?

 

[Doomed]

Had been running like this for 3 years - we got called in as they never got a cert off the original electrician and he told them to stop pestering him a few months back.
When put back correctly we found many isues that caused the RCD's to trip - shared neutrals, pinched neutral to back box in two seperate postions, switch fuse spur with neutral and earth swapped.

 

[freddo]

Commercial fryer fault. Incoming terminal block, possibly loose connections. The terminals flashed over and tripped the MCB in the end.

 

[Simon47]

Saw a safety alert recently in a large engineering business. Someone was doing some gouging*, cable was a bit short to reach where he was working, and it seems the cable wasn't secure in the trailing socket. Socket comes off leaving exposed wire ends which then falls ...
... onto the gas axe (oxy-acetylene cutting torch) he was also using on the job.
The ensuing arcing from the gouging supply cut the gas axe in half - luckily in the bit between valves and torch head. Had it dropped on the valves then it would have released copious quantities of oxygen and/or acetylene in the presence of a 'kin big arc.

What I did find interesting was that the alert didn't mention the fact that the socket shouldn't have come off the cable - only to pull the cable by the cable rather than the connector.

* For those who haven't seen it, gouging involves striking up a 'kin big arc (very much like arc welding) to melt the metal, and using a jet of compressed air to blow the molten metal out. It's a very effective way of cutting thick steel - though to say it lacks finesse would be an understatement. Example

 

[oscar21]

This definitely went wrong for my mate yesterday. He got a call out for an RCD tripping in a shop so went to have a look, managed to fix that fairly quickly and whilst he was there they said can you have a look at our lights so he did. It was a grid ceiling with 600x600 LED panels in, and the way they were wired was with a plug/socket type affair on short leads and T-pieces. The name of the plug escapes me for now but its a flat 3 pin plug same as these.

You can get short leads with a male plug on one end and a female socket on the other you then use 3/4/5/etc way splitters like above to give you ways for the lights which obviously have a male plug fitted. We fitted loads of them the other year on shop refits, I didn't like them as you couldn't really support the cables between the lights and they just ended up on top of the grid, also they were really hard to push together and engage the clips and sometimes if you pulled them apart it broke the T-splitter instead exposing the pins.

Anyway, some of the lights weren't working (not one of our jobs by the way) so he goes into the grid ceiling to have a look, grabs one of the leads at a junction and gets a big electric shock, falls off the ladders, cuts his leg and twists his knee quite badly. Turns out that the T piece had melted and exposed the connection, probably because it was never fully pushed together. He's been to A&E today and they said he has probably damaged his ligaments.

So not too sure who is at fault really, I suppose by the book he should have turned the power off, locked the MCB off and got the barriers out, tested dead etc etc but when you are fault finding like that you really need to do it live in order to find where the live bit ends and the fault begins, which he certainly did do yesterday. Or is the shop at fault for letting someone near their dangerous electrics? I'm not too sure how the shock was that bad but he reckons he thought his number was up and can't remember falling off the ladders, just getting up off the floor. He was on fibreglass steps, boots and carpet so it wasn't that, must have been the ceiling grid that was earthed, either that or it just wen't between the pins in the plug via his hand and he was being over dramatic about the shock to justify falling off the ladders.

 

[sarky spark]

From a friend’s house, sockets playing up. Pulled this out of a lath and plaster wall.