Company fuse.

[JohnW2]

Iv'e seen a demo 2.5KA short circuit with 16mm copper tails. It is a very generous process. Everyone would have received a nice piece of molten copper had it not been for the safety screens.

More education needed here, because I'm a bit confused by some of the dramatic statements being made in relation to pulling of DNO fuses in domestic installations. I can understand the risk of the fuse carrier disintegrating and/or of the exposed live parts which may be present - hence the risks of electric shock. However, there surely shouldn't be any N or E anywhere near the fuse/carrier, so how do these postulated 'explosions' due to 'megacurrents' come about?

Kind Regards, John.

 

[JohnW2]

And I absolutely condemn the practice of suppliers/DNOs charging for to remove/replace the main fuse!

Yes, if one takes a pragmatic view of the status quo, then that does seem a bit rich. It doesn't seem fair that DNOs should seemingly 'have it both ways' - if they don't/won't install isolators, then it seems a bit much for them to charge for the consequences of not installing them. That's how I see it, anyway.

Kind Regards, John.

 

[Monkeh]

Iv'e seen a demo 2.5KA short circuit with 16mm copper tails. It is a very generous process. Everyone would have received a nice piece of molten copper had it not been for the safety screens.

More education needed here, because I'm a bit confused by some of the dramatic statements being made in relation to pulling of DNO fuses in domestic installations. I can understand the risk of the fuse carrier disintegrating and/or of the exposed live parts which may be present - hence the risks of electric shock. However, there surely shouldn't be any N or E anywhere near the fuse/carrier, so how do these postulated 'explosions' due to 'megacurrents' come about?

Kind Regards, John.

What happens when you create an arc with a fixed voltage supply?

 

[westie101]

It is not unknown for there to be an unseen pre-existing fault within a cut-out.
The slight movement of removing the fuse carrier has been known to cause a short circuit in usually the lower part of the device with catastrophic results.

A landmark one of these occurred some years ago near Lancaster resulting in a colleague suffering severe burns when a 3 phase cut-out exploded as he was removing the fuses this led to far greater emphasis on wearing PPE, not rolling sleeves up and better assessing the situation.
We even changed the type of insulated gloves we use as the previous type were rarely worn as they were a poor design

 

[westie101]

then it seems a bit much for them to charge for the consequences of not installing them

I can't speak for other DNOs but we do not officially provide that service as we do not have anything to do with metering. I do know that some of the suppliers do charge for the service.

As I mentioned before the DNO's responsibility finishes at the outgoing terminal of the cut-out, the tails to the meter and the meter are the suppliers and, of course, the rest is the customers.

Privatisation was supposed to make it easy, I think we all know the truth!

 

[sparkticus]

More education needed here, because I'm a bit confused by some of the dramatic statements being made in relation to pulling of DNO fuses in domestic installations. I can understand the risk of the fuse carrier disintegrating and/or of the exposed live parts which may be present - hence the risks of electric shock. However, there surely shouldn't be any N or E anywhere near the fuse/carrier, so how do these postulated 'explosions' due to 'megacurrents' come about?

Kind Regards, John.

John, I understand and we all become complacent. just a few weeks ago I helped move a consumer unit to allow someone to reposition their inner front door frame. I was on a step ladder and momentarily and unintentionally leaned on the DNO fuse carrier. It fell apart on me. It did not short but the separation was no more than 15mm and the material forming the separation was decayed. I was horrified and called Western Power. The PFC was 2.1KA. I am happy to report that I only confirmed that with a loop tester and not a short.

People (including me) "get away" with pulling main fuses all the time but just once in a while it all goes wrong and then there are the regrets.

I used to work in the semiconductor industry on laser diodes, LEDs, TRIACs and high current SCRs. We regularly were in close proximity to 3-5KA (admittedly only at 48 - 90 volts) In 15 years in that industry I saw two very nasty accidents where people were badly burned. One person (while leaning on a bus bar) shorted his watch across a 48 volt rail which melted the watch strap into his wrist. The burns were very bad, the flesh he left on the rails was disgusting but the life threatening part was the blood loss since it fused through an artery. I have respect for high currents.

 

[westie101]

Most folk think the main danger from electricity is a shock.
Once you get to our side of the meter the biggest risk is explosion and arcing.

I work with one guy many years ago that died in a 6.6kV switchgear explosion (well he lasted 4 days in agony despite being in a specialist burns unit)

I have worked with other folk who have survived explosions but their skin never recovered from the burns.

One guy at our depot, in his early 20s, was burned 18 months ago when some switchgear failed and exploded, though only minor he still cannot expose the back of one hand to bright sunlight!

At the higher voltages the resulting explosions can demolish buildings
At 230/400V a good cable fault can lift paving stones!

 

[EFLImpudence]

leaned on the DNO fuse carrier. It fell apart on me.

THIS IS NOT GOOD ENOUGH.

I don't understand how such poor equipment is allowed.

 

[westie101]

 

[securespark]

though some meters included an isolator

Perhaps they all could.

This I feel is a fair point.

In the 90's I attended a property being furnished with a new supply cable. The DNO (then Norweb, now ENWL) also fitted a new meter and board. It was a siemens meter with split terminal covers. The LHS was DNO sealed and the RHS was generally not sealed and behind the terminal cover was a (small) isolator switch.

http://cgi.ebay.co.uk/SIEMENS-ELECT..._Measurement_Equipment_ET&hash=item439ede5536

They were very handy!

If these meters were fitted as a matter of course, that would do away with stand-alone isol's and reduce the headache of burnt-out switches.

 

[sparkticus]

leaned on the DNO fuse carrier. It fell apart on me.

THIS IS NOT GOOD ENOUGH.

I don't understand how such poor equipment is allowed.

Tell me about it. They treated it as an emergency and came out very quickly but the lady on the phone treated me like a criminal. I pointed out to her that I barely put any pressure on it and the thing looked about 100 years old

 

[westie101]

I don't understand how such poor equipment is allowed.

Age, usually nothing more

 

[sparkticus]

Age, usually nothing more

Yes, that I think is correct. It was probably 50 years old and you could see that it had been poorly treated over the years. In one sense property owners have an obligation to report these things sooner than most actually do.

 

[JohnW2]

John, I understand and we all become complacent.

Indeed, and complacency is something which we all have to be very careful about. Furthermore, I'm sure I'm far from alone in confessing that, very many moons ago ('when in my infallable youth') I did, and got away with, a good few things (some involving electricity) which were clearly very unwise.

....momentarily and unintentionally leaned on the DNO fuse carrier. It fell apart on me. It did not short but the separation was no more than 15mm and the material forming the separation was decayed.

I guess the problem must be my very limited exposure to different types of DNO fuse carrier. The ones I've come across have been such that I think even complete distintegration of the carrier would result in 'no worse' than exposure of live condctor/terminal, with no N or E anywhere near to short to.

Kind Regards, John.

 

[sparkticus]

Haven't seen that one before. I believe you can see the camera black out momentarily as the power drops or is that just the camera AGC kicking in at the start of the flash?

The person involved looked bewildered!!! (I would have been too)