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.

 

[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?