Glowing cables

[BlueToBits]

I usually do commercial work these days, but I attended a domestic call out today. I don't do this very often but I happened to be passing on the way to another job. The customer was complaining of funny smell since last night coming from her consumer unit.
I entered the house to a haze of smoke and a stench of burning plastic.
So, after removing the cover of circa 1990 squareD board, I noticed a bright yellow glow coming from the under the MCB cable entry (these boards have a top busbar). Everything was far too hot to touch. A 2.5mm cable had burned almost right through, and was glowing like a filament and had clearly been cooking the consumer's unit for quite some time. I should have taken a photo but was too alamed to think about it at the time.
I've seen the aftermath of an electrical house fire several times, but this is the first time I have seen the beginnings of what would have almost certainly have become one.

Just thought I would share this.

 

[Marvo]

Could be but I've never seen an MCB that welded closed even under short circuit fault currents......plenty of contactors but never an MCB.

 

[Knobhead]

******

 

[Knobhead]

Could be but I've never seen an MCB that welded closed even under short circuit fault currents......plenty of contactors but never an MCB.

I had a 32A MCB weld closed in a MCC panel. Fortunately the outgoing cable burnt off the terminal before too much damage was done. Thank god it did, the back up was a 1200A ACB! It still took a fair bit of time to repair the burnt cable looms. Horrible, horrible job separating all the cores to find where they went.

 

[telectrix]

had a 63A MCB was running at around 90A. never tripped.must have welded. it finally gave up the ghost. i replaced it, told client to try and reduce load till next day, when i returned to divert some of the load. he asked me why it had tripped 5 times when the old one never tripped. managed to shift 30A onto another, under loaded DB. end of problem.

 

[Antman]

It'd be interesting to see the pictures, just in the nick of time by the sounds of it.

 

[BlueToBits]

OK Here are a couple of pics
You can see that one half of the ring is still hanging on in there This is the one that was glowing. The other has disintegrated.
The 'spur' is the feed to the other 1 way 32A unit serving the cooker. (above)

 

[DurhamSparky]

mint!!!! defo a house fire in the making!!

 

[RWJ]

Nice!!!!

Worth taking the camera!!!

 

[telectrix]

nothing that can't be fixed with a bit of wd40 and some duct tape. oh and a spare MCB.LOL.

 

[Des 56]

Interesting to see the pics
Please bare with this story a little till the point at the end

A couple of weeks ago I looked at a mates house problem (was going to write looked at a "mates ring problem",but thought twice about doing that )

There was a 2.5 spur to a socket off the only ring circuit in the house to his extended kitchen (10 years installed)
Off this 2.5mm spur was 3 No double sockets for worktop appliances, feed to a garden shed which had lights+sockets with a small convector heater to keep the dogs warm

Then under worktop sockets for Washing machine fridge/freezer and Halogen cooker Hob and electric oven,mind you the cooker hood was plugged into the original double socket

His wife used to also enjoy doing the ironing from one of the sockets whilst she watched the portable telly

When i questioned him,he said they had to use the halogen elements on medium because the 30 amp fuse would blow,but otherwise never had a problem


Why I am giving this story is to make the point that even with this apparent extra super dupa high loading,there was no visible sign of overheating or melted insulation anywhere, (under the boards may be another matter) but somehow the system carried it all

I wonder whether the actual load has caused this burning or was it assisted by crap connections,because the burning appears to be confined to the area connected to the mcb
Load caused overheating should possibly be visible at other parts of the conductor

 

[mayfair]

If only all faults glowed then some of our member could save money on thermal image camera's

 

[nickblake]

bit to close for comfort this one , would be intresting to see the cause , been like that over night gee , could have died from the fumes never mind a fire , could be a multitude of causes low insulation fault drawing enough current to warm things up but not enough to trip the breaker , loose terminals , faulty mcb instead of blowing due to the fault shorted thus causing an over load to the cables mm realy any one who says why do we do calculations of cable sizes should read this post also also a good reason to carry out PIR's , they were a lucky family ,some might not have been so lucky infact they haven't , be nice to see some pics and the cause

 

[nickblake]

View attachment 5681OK Here are a couple of pics
You can see that one half of the ring is still hanging on in there This is the one that was glowing. The other has disintegrated.
The 'spur' is the feed to the other 1 way 32A unit serving the cooker. (above)
View attachment 5680

Mmmm looking at the pics i bet you any money it was caused by a loose connection on the MCB , , ... those nice QOE's were prone to that

 

[telectrix]

possibly whoever tapped the extra cables in didn't tighten it up well enough. can happen if you've got 2 cables one side and one on the other.

 

[Silly Sausage]

possibly whoever tapped the extra cables in didn't tighten it up well enough. can happen if you've got 2 cables one side and one on the other.

Good point, that spur has a much bigger csa than the other two.
I was thinking if was an overloaded cable it'd be fried along its length.