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

[Mark42]

I've been volunteering at my local village hall, installing audio and light systems. Converting what was originally an underused sports hall into a venue for bands and theatrical events.

As with most of my projects, it has got out of hand and I've now reached a load schedule of 56A for my lighting rig alone, nearly all of which is LED.

Of course there's diversity: never will all fixtures be at 100% intensity together, but adding the legacy overhead of about 50A (hand driers, kitchen kit, kettles, portable heaters) I worry that I may potentially be stressing the supply. It's only a mickey-mouse domestic single phase cutout, probably containing an 80A fuse.

In others' experience, how likely is LED inrush to blow the cutout? It would be unfortunate if a widespread strobe or flash lighting cue closed everything down by killing the building's power!

Of course careful programming can keep the load down, but it may not always be me on the Avolites desk. If we have some old-skool techno operator who goes bananas, there may be a problem.

I have wired everything on a new three-phase submain DB (with L1+L2+L3 temporarily commoned), and asked the committee to upgrade to 3 x 100A, but it will take years to get agreement, if ever.

 

[James]

I would start with a logging clamp meter and do some testing

 

[Avo Mk8]

The fusing characteristics of the main fuse means a huge surge is needed for it to blow instantaneously, and a higher sustained current than the rating of the fuse to blow it later. You'll get 100A forever from a 80A fused supply (well, until something else gives up or catches fire!). And just to take a figure at random from the graph, 300A for not more that 10 seconds.
Not that I'm recommending that!
But hopefully the equipment you have, and that brought by artists, will average out to the extent of not being a problem. As has been said, logging what's happening would probably give some peace of mind. Even a cheap clamp ammeter from Screwfix has a peak current display feature (except the instrument switches itself off after a while!), so you could keep an eye on what's happening, if you aren't already!

 

[Rockingit]

You'll only see a surge when you lamp on (old terminology!) and experience tells me that your LX load won't be anywhere near your calculation in practice. Easy way to check (as suggested above) is just to use a clamp meter - set all the movers to white and on a pan/tilt move chase and see what you're drawing. Assuming that the moles and strobes are also LED then you'll be fine.

However - personally I'd be more concerned about how much earth leakage all those cheap fixture are dropping and how you've managed that cascade over the correct A type RCD's.

ps.... Who's that rig been designed for? A resident Abba tribute??!

 

[oscar21]

I managed to blow a DNO fuse the other month, well it was my fuse but same thing. Some of the places we work in are fire damaged or flood damaged so half the time there isn't any power on when we get there, obviously people need to charge batteries, boil the kettle etc so I usually temp something on.

In this case someone had removed the cutout fuse and put the holder back into the carrier. I got a fuse out of the van, wired my temp supply and energised everything and it all worked absolutely fine all day. Came back in the next day and there wasn't any power on. Upon checking the main fuse (80A I think) had blown, no black marks anywhere, even the RCD and MCB was still on and it only supplied a couple of twin sockets anyway so couldn't have overloaded and whatever happened happened after we all left anyway.

So, I got another fuse out of the van, plugged it in and there was an almighty bang, sparks hit the ceiling and it felt like an eternity before the fuse blew, very strange, don't understand what went wrong, I thought maybe the meter had failed so disconnected that, put a very thin piece of wire across the fuse, one strand of copper flex cable I think, tried again and there was still a big bang again but not as violent.

Investigating further and the outgoing live from the cutout was shorted straight to the chassis of it, don't know how that could happen with no-one around at night but it did.

 

[littlespark]

Did you not test anything before energising?

 

[oscar21]

Did you not test anything before energising?

Would it have mattered? there wasn't anything to test really, does anyone check the cutout terminals to earth before they whack the main fuse in. Putting the main fuse back in is always an exciting moment at the best of times.

 

[westward10]

I wouldn't have even admitted to any of that.

 

[oscar21]

I wouldn't have even admitted to any of that.

For legal reasons or stupidity reasons? some people are under the impression that there are an electric police that go round lifting people that cut the seals. Some say that smart meters monitor when the power goes off and call the SAS the moment it happens, yes there is a micro switch under the cover but I had a smart meter sat on the floor for most of the day the other week whilst I rearranged everything inside the cupboard, no-one turned up, not even a traffic warden.

I've been in a couple of situations similar over the years, one all the meters were credit meters and I needed to do EICR's on several flats I had fuses/meters bridged out all over the show and someone turned up to read the meters, he said cheers mate and went on his way after I showed him where they was,, nothing ever came of it but I did find my mate hiding in the back of the van 10 minutes later.

Another example was a building contractor who bought a derelict building that had had the power cut off to it for lack of payment presumably. The meters were in the cellar which he wanted to convert, he knew an iffy DNO guy who he got to move the meters to the outside wall of the property so got it done on a Saturday morning. I went in the afternoon to fit the isolators and submains etc. I was sat there with my legs dangling into the (jointing) hole doing the isoaltors when a couple of guys from the metering company turned up to see how they could get the power back on after the builder had contacted them about re-energising the supply.

I said oh, I think it just needs the main fuses putting back into the cutouts and its ready to go, he said is all this new, I just shrugged my shoulders and said I dunno mate, I'm just here to connect the submains. And that was that, we had power again.

In situations like this I think the DNO and metering companies are well aware of "its not what you know but what you can prove" if they ever went to great expense to bring a prosecution, so unless they were to catch you red handed stealing electricity I don't think there is much they can do.

 

[westward10]

For legal reasons or stupidity reasons? some people are under the impression that there are an electric police that go round lifting people that cut the seals. Some say that smart meters monitor when the power goes off and call the SAS the moment it happens, yes there is a micro switch under the cover but I had a smart meter sat on the floor for most of the day the other week whilst I rearranged everything inside the cupboard, no-one turned up, not even a traffic warden.

I've been in a couple of situations similar over the years, one all the meters were credit meters and I needed to do EICR's on several flats I had fuses/meters bridged out all over the show and someone turned up to read the meters, he said cheers mate and went on his way after I showed him where they was,, nothing ever came of it but I did find my mate hiding in the back of the van 10 minutes later.

Another example was a building contractor who bought a derelict building that had had the power cut off to it for lack of payment presumably. The meters were in the cellar which he wanted to convert, he knew an iffy DNO guy who he got to move the meters to the outside wall of the property so got it done on a Saturday morning. I went in the afternoon to fit the isolators and submains etc. I was sat there with my legs dangling into the (jointing) hole doing the isoaltors when a couple of guys from the metering company turned up to see how they could get the power back on after the builder had contacted them about re-energising the supply.

I said oh, I think it just needs the main fuses putting back into the cutouts and its ready to go, he said is all this new, I just shrugged my shoulders and said I dunno mate, I'm just here to connect the submains. And that was that, we had power again.

In situations like this I think the DNO and metering companies are well aware of "its not what you know but what you can prove" if they ever went to great expense to bring a prosecution, so unless they were to catch you red handed stealing electricity I don't think there is much they can do.

For sheer stupidity.

 

[bill01803]

I always put a Drummond acroos the mains cut out before putting the fuse back in

 

[oscar21]

For sheer stupidity.

So what would you do? You get to site with half a dozen other lads who all have mortgages to pay and the job is due to be signed off it 4 weeks do you say hey tough luck lads, its the DNO that replaces that fuse not me but they should be along in a few weeks if you are all ok with that. or do you get some power on by hook or by crook so everyone still has a job?

The last two jobs I've turned up at they have had to get an extension lead from next door and pay the neighbour £20 a week.

 

[oscar21]

I always put a Drummond acroos the mains cut out before putting the fuse back in

Whats a drummond and would it have helped me?

 

[timhoward]

or do you get some power on by hook or by crook so everyone still has a job?

I'm going to give you a line from my old gaffer. He's dead now (from old age) and had a lifetime of electrical experience.
"Many people turn on and hope it won't go bang. We are electricians and we only energise if we know it won't go bang. It's less exciting but we live longer"

Whats a drummond and would it have helped me?

A test light. A 2 pole tester would do the same. In your case there would be a path from supply side through the tester to consumer side to earth. It would have lit up showing you were about to connect a dead short. You would go 'hang on a minute' (hopefully).

 

[littlespark]

It’s all “exciting” and “ gung ho” when things go bang…. But accidents do happen…

Why do the real DNO guys wear rubber gloves, safety goggles and a fully paid up life insurance policy.

Are you the same king of cretin that flies up the motorway at 100mph, just for the thrill?


This thread is in the public area of the forum, and you’re not painting a very professional picture of yourself at the moment.

 

[DPG]

I think more care should have been taken bearing in mind it was known the fuse had already blown once. And we all hopefully know how much current must have flowed for that to happen.

 

[oscar21]

It’s all “exciting” and “ gung ho” when things go bang…. But accidents do happen…

Why do the real DNO guys wear rubber gloves, safety goggles and a fully paid up life insurance policy.

Are you the same king of cretin that flies up the motorway at 100mph, just for the thrill?


This thread is in the public area of the forum, and you’re not painting a very professional picture of yourself at the moment.

Firstly I don't need to paint a professional picture of myself, I'm just an anonymous smuck on here, I won't lose any work over it. Secondly whats with the virtue signalling, preaching that anyone who does 100 mph is a cretin yet you more than likely do 30 past a school at kicking out time without a care in the world which is far more dangerous than 100 on a motorway.

I put a fuse in, it went bang, so what.

 

[oscar21]

I'm going to give you a line from my old gaffer. He's dead now (from old age) and had a lifetime of electrical experience.
"Many people turn on and hope it won't go bang. We are electricians and we only energise if we know it won't go bang. It's less exciting but we live longer"

A test light. A 2 pole tester would do the same. In your case there would be a path from supply side through the tester to consumer side to earth. It would have lit up showing you were about to connect a dead short. You would go 'hang on a minute' (hopefully).

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.

 

[westward10]

So what would you do? You get to site with half a dozen other lads who all have mortgages to pay and the job is due to be signed off it 4 weeks do you say hey tough luck lads, its the DNO that replaces that fuse not me but they should be along in a few weeks if you are all ok with that. or do you get some power on by hook or by crook so everyone still has a job?

The last two jobs I've turned up at they have had to get an extension lead from next door and pay the neighbour £20 a week.

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.

 

[littlespark]

Instead of 100mph, i should have said "cretins, deliberately breaking the speed limit" just for the thrill of it.... and where on earth can you do 30mph past a school at chucking out time?
Not round here.... not with all the double parked Landrovers.

 

[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.

 

[Mark42]

Blimey this thread has developed a life of its own! I only wanted some advice about a theatre installation

Arc flash? Pah! THIS is proper flash, my day job: video of me posted by a student last month. I had no idea that what I do routinely looks so stupid!

!!! I give up ... Can't get link or embed video to work !!!

 

[plugsandsparks]

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.

.

 

[Mark42]

The fusing characteristics of the main fuse means a huge surge is needed for it to blow instantaneously, ...

Thanks for the info. I'd forgotten all that as I haven't messed with cartridge fuses for a long time, and had also forgotten where to look it all up!

I now think there's no need for me to worry, I was just checking in case I'd missed something. There won't be continuous overload, and any initial surges would be very short-lived.

 

[lozarus]

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.

You ever actually done it though? Colleague of mine inadvertantly did and it blew a hole in his CKs.

I used to be like you and hate on the hi-viz brigade. Now im one of them. Funnily enough we've never slowed a job down, sent workers home or distrupted anyones salary. They've all been completed to schedule - there's just been a lot less big bangs.

Not sure why you talk about guys having to pay mortgages. Is the job is slowed down due to H&S concerns (which literally almost never happens) the guys still get paid. Obviously.

Its all irrelevant anyway as this has wind up written all over it.

 

[Mark42]

You'll only see a surge when you lamp on (old terminology!) and experience tells me that your LX load won't be anywhere near your calculation in practice. Easy way to check (as suggested above) is just to use a clamp meter - set all the movers to white and on a pan/tilt move chase and see what you're drawing. Assuming that the moles and strobes are also LED then you'll be fine. ...

Yup, everything is LED. No halogen or discharge lamps at all. Filling the truss with Rank Strand 1000W luminaires off EBay really would be the way to blow the cutout off the wall.

The picture I had to hand is old. Here's the rig as it is today; I'm still adding stuff. This is all new to me so any advice from a theatre/rock gig chap would be appreciated!

However - personally I'd be more concerned about how much earth leakage all those cheap fixture are dropping and how you've managed that cascade over the correct A type RCD's. ...

Good point. The loads are split across five circuits, each with its own RCBO.

There are three keyswitches for lighting and one each for audio and the projector, so parts of the rig can be rented to users separately, at different costs.

The keyswitches operate via cascaded 12V relays and mains contactors (that was all I had in my shed - this was a voluntary job for a charity and I donated many parts. That hurt!) No doubt I'll be told cascading those relays is bad practice. Which is probably right.

... Who's that rig been designed for? A resident Abba tribute??!

Ha Ha! Yes, probably. I LIKE mirror balls: they remind me of my youth . In heavy haze they look pretty cool actually.

I've ordered ten LED 2.5 degree sharpys which will be fun for the rock and EDM gigs we'll be doing ourselves. Where would a pro rig them?

There are a couple of other trusses at the other end of the the hall. Not sure what more to put on them yet. Any ideas?

 

[littlespark]

That really is some set up for a basketball court.

Getting a proper 3 phase supply won’t do any harm apart from the halls budget.

 

[oscar21]

You ever actually done it though? Colleague of mine inadvertantly did and it blew a hole in his CKs.

I used to be like you and hate on the hi-viz brigade. Now im one of them. Funnily enough we've never slowed a job down, sent workers home or distrupted anyones salary. They've all been completed to schedule - there's just been a lot less big bangs.

Not sure why you talk about guys having to pay mortgages. Is the job is slowed down due to H&S concerns (which literally almost never happens) the guys still get paid. Obviously.

Its all irrelevant anyway as this has wind up written all over it.

Of course I've snipped a live cable, a few times over the years, don't you keep a pair of old snips in your bag for this purpose when you aren't 100% sure its dead, we call the snips chancers.

As for people losing out on money, I was on about if the spark that turned up with the lads said he wouldn't get power on then no-one can do any work. Nearly all tradesmen are self employed, only the crap ones are cards in nowadays so if you don't work you don't get paid. Not only that if the job isn't competed on time then the contractor probably won't get any more work of the main contractor/insurance company or whatever and that can be worth hundreds of thousands of pounds.

So to say "not my problem" about energising a supply will do you no favours whatsoever. I have my limits about what I will do - like crawling in rat ---- - but being scared of the electric police isn't one of them.

As for my opinion on the H&S brigade, when I've worked on bigger sites in the past I've found they run best when the site manager has cleared off for the day, everyone is just able to get on with things away from the constant interference, they don't add anything of worth to a job. Hasn't a contractor just been killed on the Everton stadium? The H&S must be off the scale on that job but it still happens, a hi-viz didn't do much to help him.

 

[DPG]

Of course I've snipped a live cable, a few times over the years, don't you keep a pair of old snips in your bag for this purpose when you aren't 100% sure its dead, we call the snips chancers.

As for people losing out on money, I was on about if the spark that turned up with the lads said he wouldn't get power on then no-one can do any work. Nearly all tradesmen are self employed, only the crap ones are cards in nowadays so if you don't work you don't get paid. Not only that if the job isn't competed on time then the contractor probably won't get any more work of the main contractor/insurance company or whatever and that can be worth hundreds of thousands of pounds.

So to say "not my problem" about energising a supply will do you no favours whatsoever. I have my limits about what I will do - like crawling in rat ---- - but being scared of the electric police isn't one of them.

As for my opinion on the H&S brigade, when I've worked on bigger sites in the past I've found they run best when the site manager has cleared off for the day, everyone is just able to get on with things away from the constant interference, they don't add anything of worth to a job. Hasn't a contractor just been killed on the Everton stadium? The H&S must be off the scale on that job but it still happens, a hi-viz didn't do much to help him.

Nothing to do with being scared of the 'electric police' as you well know. The issue being discussed is safety.

And the Everton stadium event - nobody knows any facts about it yet so there's no point even speculating. I find your comment about 'hi viz not doing much to help him' quite disgusting to be honest.

 

[oscar21]

Nothing to do with being scared of the 'electric police' as you well know. The issue being discussed is safety.

And the Everton stadium event - nobody knows any facts about it yet so there's no point even speculating. I find your comment about 'hi viz not doing much to help him' quite disgusting to be honest.

But its true though, no matter how much you sympathise, the only time a hi-viz has any worth is if its pitch black and something like a forklift truck is operating which you step out in front of, yet everyone on site has to wear one, even working alone in a room, they are useless and just a hindrance, the amount of times mine has got caught round door handles is crazy.

As for the safety aspect, no-one yet has said why its dangerous to other people when I put the fuse back in, I don't count as it would be self inflicted and that's down to me.

 

[timhoward]

As for the safety aspect, no-one yet has said why its dangerous to other people when I put the fuse back in, I don't count as it would be self inflicted and that's down to me.

There was a fault to earth. It happened to be low enough resistance to blow the main fuse. You said yourself it seemed to take a while to go. During this time every bonded piece of metalwork was at mains potential.
A slightly higher resistance value fault could have left the main fuse intact for many minutes.