Record for most underrated cable?

[NealHarman]

When we moved into this house, there was this dubious looking socket - and it didn't work. Well, never mind it looked a bit dodgy and it was in a stupid place near the cooker. Finally got to take if off yesterday - and it was spurred off the cooker point in telephone cable. I think I know why it doesn't work now... and when I hack the plaster off I'll find a nicely charred bit. They hadn't even bothered to double up the conductors (or bothered with an earth for that matter - even with four spare conductors).

This, I hope, is going to be the stupidest thing I find in this house. (I'd thought the loft sockets on a lighting circuit in 1mm and the socket radial bypassing the CU was bad, but I guess you see all this pretty often.)

Sorry, just had to rant to someone about this,
Neal

 

[andy]

When we moved into this house, there was this dubious looking socket - and it didn't work. Well, never mind it looked a bit dodgy and it was in a stupid place near the cooker. Finally got to take if off yesterday - and it was spurred off the cooker point in telephone cable. I think I know why it doesn't work now... and when I hack the plaster off I'll find a nicely charred bit. They hadn't even bothered to double up the conductors (or bothered with an earth for that matter - even with four spare conductors).

This, I hope, is going to be the stupidest thing I find in this house. (I'd thought the loft sockets on a lighting circuit in 1mm and the socket radial bypassing the CU was bad, but I guess you see all this pretty often.)

Sorry, just had to rant to someone about this,
Neal

most under-rated cables.... 4MM T+E as meter tails.


and a 9KW shower

 

[supersparks]

most underated cable

1mm twin feeding a massive 10kw+ hob over 5 meters

this year

 

[2scoops0406]

My parents utility room in their house (6 13 amp sockets, washing machine etc) was running off a spur comprising of bell wire (not sure what the proper term is).

 

[NealHarman]

Now I've calmed down a bit, it occurs to me that what I found wasn't really dangerous as such - which all those others are.

Neal

 

[mapj1]

However, whether these horrors were done by ignorant DIY types or by unscrupulous people claiming to be electricians who actually took money for the job, we will never know. The only scrap of satisfaction we can take from this is that there was no serious fire in any of these cases.
This latter is a merciful consequence of our general tendency to over design massively in terms of domestic loading. You might be amused to know that the RECs size their substations based on a couple of kilowatts per house on average, (so near me for example a 0.5Mw subs drives ~180 houses with roughly a third on each phase and a further 10 larger buildings with phase supply)
On that basis of less than 10A per supply, each house supply could be wired in 1mm - of course it couldn't really, as the peak load is much higher, but it makes you think a bit when we worry about a 2:1 diversity in the consumer unit.
(I presume the oil in the substation heats up slowly enough that its OK with the TV adverts peak of kettles going on etc.)
I've seen 2.5mm feed a 60A consumer unit, from henley blocks from the meter tails. Replaced it with 16mm, and felt much better, though it showed no sign of having been overheated.

 

[kendor]

Most Underated cable: Bell wire feeding a mains rated Alarm bell circuit through a time switch with bell wire feed in from wrong side of header so backed up by sub station fuses!

 

[mapj1]

kendor, it might even have been worse than that , many substations don't have fuses as such on the LV (415/240) side - they rely on the stray inductance of the transformer to limit the fault current. So a 0.5Mw subs may have a short circuit current limited to about 20 times the nominal load (transformer regulation about 5%), but nothing to actually 'blow' on the secondary side to cut it off. I presume this is no longer the practice in modern subs, but it certainly was at one time, and I think a few overloaded transformers have actually caught fire over the years as a consequence - usually where new housing has been added but the transformer not upgraded to keep in step.

 

[ninebob]

Remember this one?

 

[Big_Spark]

Most under-rating I have ever seen was many years ago as an apprentice.

A wood processing plant had a liitle fire which activated the alarm and the sprinkler systems, but this made the fire spread elsewhere...why you may wonder...

Well it tuyrned out the star-delta connected 21kW pump foe the sprinklers was fed in 2.5mm singles via conduit, into trunking then connected, via JB, to T&E clipped to wooden office partitions.

The p[ump had never been run apparently and when it did the T&E, as well as all the singles insulation, ignited. The singles in the conduit simple fizzled I guess from the mess we stripped out later, but those in the trunkling ignited the adjacent cables, and the T&E ignited the wooden panels.

Obviously the pump failed and the sprinklers stopped rather quickly i would assume.

We were on that Job for about 3 months wiring the new building and the surviving part that nhad been saved, ripping out all the old melted cables.

I don't think I can ever forget the stench in that place...

 

[Adam_151]

21KW total?, so 7kw per phase, somewhere around 30AMP, 2.5mm is rated at about 20A, ins't it, I would expect it to just heat up a little too much, maybe brown a bit, but not set fire to wood (well not unless it had been running for hours)?

Unless I've mis-understood, and the cables were carrying 90A (21kw), then I could imagine it causing that sort of damage.

Most certainly undersized whatever, I would imagine for the first way, it would be 6mm minimum and the second 25mm minimum?

 

[kendor]

kendor, it might even have been worse than that , many substations don't have fuses as such on the LV (415/240) side - they rely on the stray inductance of the transformer to limit the fault current. So a 0.5Mw subs may have a short circuit current limited to about 20 times the nominal load (transformer regulation about 5%), but nothing to actually 'blow' on the secondary side to cut it off. I presume this is no longer the practice in modern subs, but it certainly was at one time, and I think a few overloaded transformers have actually caught fire over the years as a consequence - usually where new housing has been added but the transformer not upgraded to keep in step.

Blimey!

 

[jime17]

seen a 9kw shower run in flex, dangling in the steel bath and poked thru a hole in the wall. When I looked round the other side, It was plugged into a plug top in the kitchen. Which wasnt even in the ring. it was a spur.

 

[Big_Spark]

21KW total?, so 7kw per phase, somewhere around 30AMP, 2.5mm is rated at about 20A, ins't it, I would expect it to just heat up a little too much, maybe brown a bit, but not set fire to wood (well not unless it had been running for hours)?

Unless I've mis-understood, and the cables were carrying 90A (21kw), then I could imagine it causing that sort of damage.

Most certainly undersized whatever, I would imagine for the first way, it would be 6mm minimum and the second 25mm minimum?

Adam, 21kW PER PHASE (mistype sorry)

Also, 21kW total on 3 phase would not be 7kW per phase either, 7kW per phase would be 12.1kW total.

21kW total would be 12.138kW per phase.

 

[Steve]

once on holiday in Fuerteventura i noticed that the entire stage setup and music system in the hotel was running on an extension reel, partly rolled up, wired in the thinner variety of table lamp flex! All the stage lights (about 10), amp system (4 big speakers), everything, i was amazed. Then again, its not as bad as some of the other situations on here. Also, in these places, sockets hanging off walls in public areas might get left a couple of weeks, so its not surprising really!!