How easy is it to blow the DNO's cutout?

[plugsandsparks]

And yet everyone I know has a story of a big bang that happened to them, I've never met an electrician yet that hasn't had quite a big shock at some stage despite being a professional, I'll bet you have, sometimes things go wrong and 99.9% of the time you live to tell the tale, ---- happens.

As for the tester, wouldn't it light up anyway with a path through the meter as it was still wired in at that stage. The fuse I replaced (twice) was out of one of those isolatotor units where you get a pack of three 60/80/100 and when it didn't work my initial reaction was it must have been a cheap chineese fake fuse that just stopped working, no other explanation really.

Can you explain how a perfectly working cutout suddenly developed an absolute dead short to ground overnight without anyone being anywhere near it. I had a prod around inside it to try and see and the top of the carrier still looked like it was sat on an insulator to me.

I think what is alarming some is the acknowledgement by some who have survived a major event. When you have personally experienced an event and live, you have a different attitude to going for a fuse replacement without testing first. OK 80A or 100A fuses wont bring the house down, but what size fuse would you consider too big to risk ? - You may think its OK the fuse will hold itself together thus containing the explosion but sometimes it does not end there. The risk of a blinding flash and hot metal splatter, you will live from but you will end up with an unwanted tan and a visit to A&E to get the metal out of your eyes.

Personally i have taken out one head fuse and one substation fuse in a long career, neither were due to energising , mistakes made under pressure.
I think you will find - energising a supply without testing to be offensive to some and do hope you continue to be lucky.

 

[oscar21]

Not my problem.
You have a ruptured service head fuse, your solution put some copper across it, result bang. Not exactly level headed thinking is it you don't sound a very safe person to be in close proximity to.
Pray tell me you don't actually train people.

Ah a stickler for the rules, I'll bet you love shutting down a site and sending everyone home because a bit of brown sleeving was missing off a light switch. In what world can you delay a job indefinitely, cost a firm potentially loads of future work and put people out of a job just because you wont bend the rules.

When are people going to realise they are hired because they CAN do the job, not because they can't or wont. When firms say they want a good job doing they mean a quick job with zero comebacks, they dont mean a job that takes 10 times longer than expected because the spark is meticulous about everything. I found this out with masses of experience, the moment you start telling contractors that something cant be done you get dropped quicker than a hot potato, if you tell them you can do the job you can name your price.

 

[DPG]

Ah a stickler for the rules, I'll bet you love shutting down a site and sending everyone home because a bit of brown sleeving was missing off a light switch. In what world can you delay a job indefinitely, cost a firm potentially loads of future work and put people out of a job just because you wont bend the rules.

When are people going to realise they are hired because they CAN do the job, not because they can't or wont. When firms say they want a good job doing they mean a quick job with zero comebacks, they dont mean a job that takes 10 times longer than expected because the spark is meticulous about everything. I found this out with masses of experience, the moment you start telling contractors that something cant be done you get dropped quicker than a hot potato, if you tell them you can do the job you can name your price.

You sound like a liability to be honest.

A missing bit of brown sleeving is nowhere near the same thing as replacing a DNO fuse on to known, or suspected, fault.

 

[oscar21]

You sound like a liability to be honest.

A missing bit of brown sleeving is nowhere near the same thing as replacing a DNO fuse on to known, or suspected, fault.

Depends what you mean by "a liability" I would be way more concerned by a man with a hi-viz and a clipboard than I ever would by a tradesman that used a saw without a guard.

and what exactly is wrong with putting a fuse back into a faulty holder, the bang? are we not allowed to frighten people any more. Yes there were some sparks for a few seconds but so what, some even wen't down my tshirt, how could that effect anyone else but me.

Actually I don't think the bang was even all that loud, it was more of a roar actually, I've certainly had bangs just as loud when cutting a live socket cable.

 

[westward10]

Ah a stickler for the rules, I'll bet you love shutting down a site and sending everyone home because a bit of brown sleeving was missing off a light switch. In what world can you delay a job indefinitely, cost a firm potentially loads of future work and put people out of a job just because you wont bend the rules.

When are people going to realise they are hired because they CAN do the job, not because they can't or wont. When firms say they want a good job doing they mean a quick job with zero comebacks, they dont mean a job that takes 10 times longer than expected because the spark is meticulous about everything. I found this out with masses of experience, the moment you start telling contractors that something cant be done you get dropped quicker than a hot potato, if you tell them you can do the job you can name your price.

You like to take things out of context.
You are a CAN doer (is that a word) and there is nothing wrong with this I think we are all proactive in finding solutions to "get the job done".
Your CAN doing was to stick some copper wire across a service head fuse because you are reckless and do not think of the consequences and this makes you a dangerous person, the big man seeking the big pat on the back.

 

[DPG]

Depends what you mean by "a liability" I would be way more concerned by a man with a hi-viz and a clipboard than I ever would by a tradesman that used a saw without a guard.

and what exactly is wrong with putting a fuse back into a faulty holder, the bang? are we not allowed to frighten people any more. Yes there were some sparks for a few seconds but so what, some even wen't down my tshirt, how could that effect anyone else but me.

I think you're trolling.

 

[oscar21]

You like to take things out of context.
You are a CAN doer (is that a word) and there is nothing wrong with this I think we are all proactive in finding solutions to "get the job done".
Your CAN doing was to stick some copper wire across a service head fuse because you are reckless and do not think of the consequences and this makes you a dangerous person, the big man seeking the big pat on the back.

But the building site is a dangerous place, no-one there is under the illusion that its safe, I've dodged falling bricks one more than one occasion, tripped over stuff left sticking up that shouldn't be there, got cut by nails left sticking out, you name it its probably happened to me in the past.

Edit, I'm interested in the consequences bit, what consequences could actually have happened? no-one would have got a shock, the fault was just at the cutout, no-one would have been blinded because no-one was stood over me, same goes for the sparks and as for the house, yes I suppose it could have burned down but that wouldn't have really mattered due to the fact it was already burned down.

 

[westward10]

But the building site is a dangerous place, no-one there is under the illusion that its safe, I've dodged falling bricks one more than one occasion, tripped over stuff left sticking up that shouldn't be there, got cut by nails left sticking out, you name it its probably happened to me in the past.

Edit, I'm interested in the consequences bit, what consequences could actually have happened? no-one would have got a shock, the fault was just at the cutout, no-one would have been blinded because no-one was stood over me, same goes for the sparks and as for the house, yes I suppose it could have burned down but that wouldn't have really mattered due to the fact it was already burned down.

If you don't know the possible consequences of what you did then this is a reflection of your competence. I doubt one person who read your post regarding this fuse thought what a clever thing to do. I suspect most, like me thought why on earth would you admit to something like that.

 

[James]

I have taken out a 100A service fuse
board was off but the 30 or 40mm disk from the holesaw fell down the back of the board and rattled into position across the feeder bus bars.

I phoned central networks, they came out within 30 minutes.
explained what had happened to the engineer and he said something like ---- happens and then changed the fuse for me.
sometimes it is easy to do the right thing.

 

[timhoward]

And yet everyone I know has a story of a big bang that happened to them, I've never met an electrician yet that hasn't had quite a big shock at some stage despite being a professional, I'll bet you have, sometimes things go wrong and 99.9% of the time you live to tell the tale, ---- happens.

Yes. I've taken out a supplier fuse when an entire installation was reverse polarity, and certainly mistakes were made leading up to this, but I learned from it.
I get that you left things working one evening, and the next morning for no apparent reason everything was dead.
Red flag number 1 was obviously that supplier fuse had blown. That would immediately make me think something very significant has happened.
Red flag number 2 was that the RCD and MCB were still in the ON position. So the cause must be upstream of them. This would put me in "something exceptionally unique and wacky has happened" mode and caution levels would rise to paranoid levels.

The absolute last thing I'd do is bung another fuse straight in and 'see what happened'. Continuity/IR testing at your incomer on your CU would be where my mind when next.
As for creating your own low value fuse, still without having any idea what caused the fault or finding a way to measure it, well I'm honestly rather stunned.

Out of interest, what was causing the short, the end of the tails, or the terminal itself?
Was the cut-out safe for continued use afterwards?

 

[oscar21]

Yes. I've taken out a supplier fuse when an entire installation was reverse polarity, and certainly mistakes were made leading up to this, but I learned from it.
I get that you left things working one evening, and the next morning for no apparent reason everything was dead.
Red flag number 1 was obviously that supplier fuse had blown. That would immediately make me think something very significant has happened.
Red flag number 2 was that the RCD and MCB were still in the ON position. So the cause must be upstream of them. This would put me in "something exceptionally unique and wacky has happened" mode and caution levels would rise to paranoid levels.

The absolute last thing I'd do is bung another fuse straight in and 'see what happened'. Continuity/IR testing at your incomer on your CU would be where my mind when next.
As for creating your own low value fuse, still without having any idea what caused the fault or finding a way to measure it, well I'm honestly rather stunned.

Out of interest, what was causing the short, the end of the tails, or the terminal itself?
Was the cut-out safe for continued use afterwards?

Yes there was a red flag moment but think about it, it worked fine, its probably worked fine since the 50's, yes the house had had a fire but it didn't get to the mains cupboard, the old plastic CU was still intact. So what could cause a 80A fuse to blow in the middle of the night with no-one around and absolutely no load on it, its not like the cut out has moving parts that had failed.

My conclusion to the red flag moment was it has to be a faulty fuse, so I replaced it. As for the very thin fuse wire trial, I thought that was quite a good idea, couldn't have been more than an amps worth of wire, I disconnected everything, even the tail out of the top of the fuse holder and it still went with a bang but with a lot less sparks and arcing this time.

s for the problem, I have no idea, I still cant fathom what went wrong, I got the office to call the DNO out and I wrote on the cut out "do not energise" By the time I came back to second fix it had a brand new head on it.


I still don't get all the hoo-ha about it though, it seems some people are ---- scarred of a big bang, you see it when someone is going to cut a cable which might be live with insulated snips, try as they might, they just can't bring themselves to do it even though they know they are perfectly safe from injury, its the bang you see.

 

[pc1966]

I still don't get all the hoo-ha about it though, it seems some people are ---- scarred of a big bang

You might want to look up arc-flash injuries. Actually, you don't.

The stats I remember from the USA was that about 80% of deaths suffered by electricians were due to burns, not shock. Now the situation UK versus USA is not quite identical as the USA has more issues of arc-flash for various reasons, but if you have seen what a high energy fault can do on a test rig, etc, you REALLY do not want to be part of it.

 

[littlespark]

If you make a big bang like that in full earshot of plumbers, joiners, builders… you’ll either

A- get the p ss ripped out for months on end
B- no one wants you back on a job because even they think it was dangerous.

 

[pc1966]

Sound is not quite in sync (earlier than video) due to video compression delay artefacts on cheap dashcam, but here is an illustration of why you wear PPE if working on live power circuits:

 

[James]

I am not sure that you realise the damage that closing a fuse on to a fault can cause.
on this occasion it seems like you were lucky.
these things can end in loss of life, if your lucky it’s just loss of face (sometimes literal)
my first thoughts are that you are an idiot, after further thought I think you are more educated than the average idiot however have little concern about the effects of your actions and are therefore just a risk taker.
good thing you have found employment because if you start telling prospective employers about your antics they might turn you down.

 

[oscar21]

I am not sure that you realise the damage that closing a fuse on to a fault can cause.
on this occasion it seems like you were lucky.
these things can end in loss of life, if your lucky it’s just loss of face (sometimes literal)
my first thoughts are that you are an idiot, after further thought I think you are more educated than the average idiot however have little concern about the effects of your actions and are therefore just a risk taker.
good thing you have found employment because if you start telling prospective employers about your antics they might turn you down.

I really do think most people have never worked on smaller informal sites that don't have the hi-viz brigade looking after them. You wouldn't believe what goes on regarding safety or lack of it. The labourer fell though some joists the other day right up to his -------s and brought a ceiling down with him, did anyone get upset? of course not.

I must live in a different universe to most people, just the other day (admittedly working at home) me and a mate got my RSJ steel into position by lifting it up a block at a time from either end until it was about two meters high, wobbled all over the show but it saved £100 on a genie, it wasn't even me that wanted to do it that way but I got called soft for not just getting on with it.

 

[timhoward]

Sound is not quite in sync (earlier than video) due to video compression delay artefacts on cheap dashcam, but here is an illustration of why you wear PPE if working on live power circuits:

I was looking for that video earlier, but couldn't find it.
There's another one where there is no way the person standing where the fireball happened survived, and it's simply too horrific to share a link to.

I really do think most people have never worked on smaller informal sites that don't have the hi-viz brigade looking after them.

This is the last place you want to generalise, we have forum members doing just about everything possible! I'm a sole trader and rarely do site work.

So what could cause a 80A fuse to blow in the middle of the night with no-one around and absolutely no load on it, its not like the cut out has moving parts that had failed.

So far my best wild guess is that things got marginally disturbed when the temporary supply was hooked up, and some kind of significant vibration occurred causing a further minor shift in either the terminal or the tails and BANG.

The bottom line is that a closing on a dead short or even a moderate load load holding an 80A fuse in your hand to complete the circuit is just damned dangerous, and the extent you are arguing against this basic fact leads me to believe you have no intention of ever taking it on board. I don't have anything further to add so won't be debating this any further.

 

[plugsandsparks]

I think in this case, the guy needs more experience, which i think he will get soon enough. He never did answer the question of what size fuse would he baulk at energising without IR testing first, still, cannot fault the attitude, like the guy jumping out of a 30 storey building...... so far so good, lol

 

[oscar21]

I think in this case, the guy needs more experience, which i think he will get soon enough. He never did answer the question of what size fuse would he baulk at energising without IR testing first, still, cannot fault the attitude, like the guy jumping out of a 30 storey building...... so far so good, lol

More experience, I'm 52 and have had more than most.

Its no good asking this question, how can you test a cut out before you put the fuse back in, I'll pull plenty of fuses out over the next months and years an I'll put plenty back in again, I'm not about to do a full forensic on every little thing I do from now on on the off chance that a 0.00001% fault will occur. I'd rather take my chances.

 

[oscar21]

I was looking for that video earlier, but couldn't find it.
There's another one where there is no way the person standing where the fireball happened survived, and it's simply too horrific to share a link to.


This is the last place you want to generalise, we have forum members doing just about everything possible! I'm a sole trader and rarely do site work.

So far my best wild guess is that things got marginally disturbed when the temporary supply was hooked up, and some kind of significant vibration occurred causing a further minor shift in either the terminal or the tails and BANG.

The bottom line is that a closing on a dead short or even a moderate load load holding an 80A fuse in your hand to complete the circuit is just damned dangerous, and the extent you are arguing against this basic fact leads me to believe you have no intention of ever taking it on board. I don't have anything further to add so won't be debating this any further.

With the greatest respect I won't be taking it onboard, I just dont see how you can guard against this, it was one of those "---- happens" moments and will more than likely never happen again in my lifetime.