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

[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.

 

[westward10]

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.

You don't get the hoo-ha because you don't have knowledge base.

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.

You are either a troll or not the sharpest tack in the box.

 

[oscar21]

You don't get the hoo-ha because you don't have knowledge base.

You are either a troll or not the sharpest tack in the box.

you cant just call someone names, come up with a reason for what I did was dangerous to others, TimHoward came up with a good reason regarding the bonding but it was an empty house, the only thing connected was a 2 way mains unit and a twin socket, no ,metalwork anywhere that was bonded, no gas meter, no taps, no nothing so that was never a danger.

There must be some danger if everyone is so angry with me.

 

[lozarus]

you cant just call someone names, come up with a reason for what I did was dangerous to others, TimHoward came up with a good reason regarding the bonding but it was an empty house, the only thing connected was a 2 way mains unit and a twin socket, no ,metalwork anywhere that was bonded, no gas meter, no taps, no nothing so that was never a danger.

There must be some danger if everyone is so angry with me.

Call someone names? You literally just said that all the good electricians are self employed and only the cr*p ones are on the books.

Myself and many others here are employees. And well respected and qualified in our trade but prefer PAYE employment.

Your employment type is irrelevant.

I suppose you think this 'testing' is a load of hogwash too and its much bettter to just power everything on and see if anything goes bang?

 

[HappyHippyDad]

you cant just call someone names, come up with a reason for what I did was dangerous to others, TimHoward came up with a good reason regarding the bonding but it was an empty house, the only thing connected was a 2 way mains unit and a twin socket, no ,metalwork anywhere that was bonded, no gas meter, no taps, no nothing so that was never a danger.

There must be some danger if everyone is so angry with me.

Correct , and well done for calming down and having a proper think. Stay cool man

 

[Rockingit]

... 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?

Glasgow ABC - largest mirrorball in Europe at 4m! It is true that you get a lot of bang for buck with a simple mirrorball, I think it's all the white that's so surprising, especially if you're talking about EDM gigs.

I realise you've only a small space to work in and limited funds but I think I'd be tempted to look at adding a mid truss to get extra depth and separation above stage. Move everything that's currently on the US truss to the new MS truss except for some PARS and then stick your Sharpies in a 3-4-3 pattern on the US - that way you can do some ACL looks if your style is old skool

 

[Mark42]

I think it's all the white that's so surprising

Ha ha! You mean the stage dressing? It took ages for the committee to let me paint the front of the stage and the side panels grey for a start. They were gloss white Dulux, threw every bit of stray light back into your face, and looked ridiculous. Next is to paint the rear exposed walls dark grey as well.

I realise you've only a small space to work in and limited funds but I think I'd be tempted to look at adding a mid truss to get extra depth and separation above stage.

You're right - this is a rural village hall (!) and it's only happened at all because I paid for everything out of my own pocket, with the hall then paying me back as they see the benefit of having this kit, and them making money from gigs that could not have been done before. Without my JFDI attitude nothing would ever have happened. This is all a bit of a hobby for me, and something I've wanted to do since helping with lighting at school in the 70's, and it's fun. Compared with PAR cans and cinemoid, modern RGBW moving lights are amazing!

I'm not keen on putting a lot more structure in, as I can't face any more arguments with the committee about it! But your idea of the mid truss is great. I wish I'd known about that before.

I could put two or three single ali tubes running US-DS, just clamped on top of the existing trusses.

Or maybe one length of single ladder truss L-R hung off the existing US-DS rails, but it wouldn't take much weight.

Those five 350W MLs (which are beam-spot-wide zoom fittings, not sharpies) on the US truss are heavy, so they probably have to stay where they are as that's the only truss that can take the load.

Move everything that's currently on the US truss to the new MS truss except for some PARS and then stick your Sharpies in a 3-4-3 pattern on the US - that way you can do some ACL looks if your style is old skool

What does 3-4-3 mean? Three on the stage R vertical, four on the horizontal truss, then three on the stage L vertical? Or all on the horizontal? Any of that could be done as-is, I could rig the sharpies on top of the existing US truss.

Although there are two lasers to go on top of the verticals first, to do the liquid sky thing. Yup: old skool is the way

What I really need is a Avolites guru to advise on the rig and set up some looks and chases in venue mode, while I learn Titan myself (I'm doing the online course now). This is all new to me . Any Avolites dudes in South Norfolk who fancy a day's consultancy work?

 

[littlespark]

You got an expert involved now with @Rockingit contributing.

When we had the caravan park, our club/bar was built from portacabins with low ceilings.
I managed to source a half-glitterball, did the job.

 

[Rockingit]

You got an expert involved now with @Rockingit contributing.

When we had the caravan park, our club/bar was built from portacabins with low ceilings.
I managed to source a half-glitterball, did the job.

Was that flattery mate? Because you know I'm a sucker for a flirt....

 

[Rockingit]

Ha ha! You mean the stage dressing? It took ages for the committee to let me paint the front of the stage and the side panels grey for a start. They were gloss white Dulux, threw every bit of stray light back into your face, and looked ridiculous. Next is to paint the rear exposed walls dark grey as well.

You're right - this is a rural village hall (!) and it's only happened at all because I paid for everything out of my own pocket, with the hall then paying me back as they see the benefit of having this kit, and them making money from gigs that could not have been done before. Without my JFDI attitude nothing would ever have happened. This is all a bit of a hobby for me, and something I've wanted to do since helping with lighting at school in the 70's, and it's fun. Compared with PAR cans and cinemoid, modern RGBW moving lights are amazing!

I'm not keen on putting a lot more structure in, as I can't face any more arguments with the committee about it! But your idea of the mid truss is great. I wish I'd known about that before.

I could put two or three single ali tubes running US-DS, just clamped on top of the existing trusses.

Or maybe one length of single ladder truss L-R hung off the existing US-DS rails, but it wouldn't take much weight.

Those five 350W MLs (which are beam-spot-wide zoom fittings, not sharpies) on the US truss are heavy, so they probably have to stay where they are as that's the only truss that can take the load.

What does 3-4-3 mean? Three on the stage R vertical, four on the horizontal truss, then three on the stage L vertical? Or all on the horizontal? Any of that could be done as-is, I could rig the sharpies on top of the existing US truss.

Although there are two lasers to go on top of the verticals first, to do the liquid sky thing. Yup: old skool is the way

What I really need is a Avolites guru to advise on the rig and set up some looks and chases in venue mode, while I learn Titan myself (I'm doing the online course now). This is all new to me . Any Avolites dudes in South Norfolk who fancy a day's consultancy work?

View attachment 109998

Some cheap 2-300mm tri truss overslung between the two US / DS trusses will give you enough structure to rig an under-slung additional L<>R truss, also gives flexibility to move the whole lot around. What I meant by 3-4-3 was in the horizontal line in three groups, so 3 - space - 4 - space - 3. As for control, I abandoned Avo many years ago and have owned Chamsys ever since but there's many groups to be found on FB - lot's of kids out there with all the button pushing knowledge (and not much else.....) you can glean off. Sherbert dip and a bottle of fizz and they'll be all over that......

 

[Avo Mk8]

I abandoned Avo many years ago and have owned Chamsys ever since

You heartless man! Did I not measure up?

 

[OnlQQker]

Video mapping can work wonders, and all that's needed is a projector, socket and after effects. Takes a while to do the mapping, but if you map parts of the building that never alter then you can use this forever.

I used the ceiling at my daughters prom in a nightclub once, all the kids faces were projected onto the ceiling and morphed into each others with a universe background, I'd then change position and throw the projection over to different walls whilst leaving the universe playing out on the ceiling with shooting stars etc. It caused the same reaction as video below. The projectors are a lot cheaper if you approach the manufactures directly, you'll need a large venue projector, the small one's give you less coverage. If you suspend something clear from the ceiling, say a clear piece of perspex that is see through, you can start messing around with 3d mapping. Unless you've seen it live youtube video doesn't really capture it very well!

 

[DPG]

Video mapping can work wonders, and all that's needed is a projector, socket and after effects. Takes a while to do the mapping, but if you map parts of the building that never alter then you can use this forever.

I used the ceiling at my daughters prom in a nightclub once, all the kids faces were projected onto the ceiling and morphed into each others with a universe background, I'd then change position and throw the projection over to different walls whilst leaving the universe playing out on the ceiling with shooting stars etc. It caused the same reaction as video below. The projectors are a lot cheaper if you approach the manufactures directly, you'll need a large venue projector, the small one's give you less coverage. If you suspend something clear from the ceiling, say a clear piece of perspex that is see through, you can start messing around with 3d mapping. Unless you've seen it live youtube video doesn't really capture it very well!

I like that - very impressive.

 

[davesparks]

As for control, I abandoned Avo many years ago and have owned Chamsys ever since

I've heard from a few people that Avo ain't what they used to be these days, I guess they must have struggled a bit with the shift to LED and not be shifting any where near as many ART racks!

I've got an early tiger touch somewhere that still gets a bit of use, and of course the obligatory rollacue pearl with wooden sides I want to build in to a coffee table.

Not that I've operated any LX desk in years, I'm very much settled in the 'I'll build it, someone else can operate it' camp these days.

 

[Simon47]

And to think, the last lighting desk I used was a 12 channel manual Furse - and we thought it was the bee's knees having two sets of faders with a master each making crossfades easy ! Still a big step up from rheostats.
But the thyrister units didn't keep your coffee warm.

 

[Gavin John Hyde]

I blew a DNO fuse yesterday as it happens, fitting a change over switch and the little copper busbars at teh bottom were slightly out of alignment, powered up and heard faint thud/pop.. meter was blank and found fuse blown. called SSEN who were there in half hour to replace. it blew instantly.

 

[Rockingit]

And to think, the last lighting desk I used was a 12 channel manual Furse - and we thought it was the bee's knees having two sets of faders with a master each making crossfades easy ! Still a big step up from rheostats.
But the thyrister units didn't keep your coffee warm.

My first outing at lighting involved an 11yr old me who very literally knew enough to be dangerous very nearly setting the school hall on fire by over-loading the plug and play green ginger sliders and leaving them at various stages of extra-hot and buzzing for three hours........

 

[Simon47]

I do recall one time there was a group of students who'd formed a band, and they had a gig in the hall. They'd asked to use the stage lighting, and reluctantly had been given permission on the condition that there was to be no flashing of the lights - the English teachers who were in charge of Drama were terrified of blowing a bulb, we'd just bought a couple of spares at something like £20 each in early 80s money. Anyway, I got nominated as the responsible person to operate the lighting for them.
The next morning was April 1st. As I went into a physics lesson (our physics teacher was in charge of technical matters relating to the hall), I casually mentioned that we'd blown one of those expensive bulbs - and of course, he fell for it. But it backfired on me, because at break time, he went and did the same to one of the drama teachers - only he told her we'd blown two bulbs. I got a small telling off for raising her blood pressure.

Ah, the things we could get away with back then. Our control booth was at the back of the ranked seating, and the only way in and out was through the audience. But we realised that if we left a window open on an upstairs corridor, and used the fire door right next to the door into our booth, we could walk across the flat roof - typically in the dark, and with no rail at the side where it was a nice drop onto solid paving.

Back to the question, I blew a main fuse once - through a moment's inattention. I normally attach a spare MCB to the busbar with a bit of wire to the earth bar for R1+R2 tests, but following a house move I didn't have it with me when I was doing an EICR. Having done live tests (Zs, Ze), something must have distracted me, and I went to apply a L-E lead so I could go round doing R1+R2 tests ... with the power still on. I was actually surprised how little of a flash and bang it made, and how little it took out of the crock clip.
What was more irritating was the attitude of the DNO when I called them. The person at the other end flat out refused to take my number, insisting on me giving the one that matched their records - of the tenant who was at work. The engineer then proceeded to go to the wrong street (not uncommon as the postcode isn't too accurate and the address is confusing). And as the tenant had their phone off due to the nature of their work, they couldn't get hold of me.
So after no-one has turned up for a while, I rang them back, to be told he'd been, there was no-one in, and he'd gone - and perhaps they'd be able to get someone back tomorrow. At which point I used "quite persuasive" language until they agreed to call the engineer and get him to return. The tenant had now got the message they'd left, and between us we managed to work out where the engineer was, walk down, and redirect him.
For good measure, he couldn't find any seals to reseal the cutout.

 

[nicebutdim]

I do recall one time there was a group of students who'd formed a band, and they had a gig in the hall. They'd asked to use the stage lighting, and reluctantly had been given permission on the condition that there was to be no flashing of the lights - the English teachers who were in charge of Drama were terrified of blowing a bulb, we'd just bought a couple of spares at something like £20 each in early 80s money. Anyway, I got nominated as the responsible person to operate the lighting for them.
The next morning was April 1st. As I went into a physics lesson (our physics teacher was in charge of technical matters relating to the hall), I casually mentioned that we'd blown one of those expensive bulbs - and of course, he fell for it. But it backfired on me, because at break time, he went and did the same to one of the drama teachers - only he told her we'd blown two bulbs. I got a small telling off for raising her blood pressure.

Ah, the things we could get away with back then. Our control booth was at the back of the ranked seating, and the only way in and out was through the audience. But we realised that if we left a window open on an upstairs corridor, and used the fire door right next to the door into our booth, we could walk across the flat roof - typically in the dark, and with no rail at the side where it was a nice drop onto solid paving.

Back to the question, I blew a main fuse once - through a moment's inattention. I normally attach a spare MCB to the busbar with a bit of wire to the earth bar for R1+R2 tests, but following a house move I didn't have it with me when I was doing an EICR. Having done live tests (Zs, Ze), something must have distracted me, and I went to apply a L-E lead so I could go round doing R1+R2 tests ... with the power still on. I was actually surprised how little of a flash and bang it made, and how little it took out of the crock clip.
What was more irritating was the attitude of the DNO when I called them. The person at the other end flat out refused to take my number, insisting on me giving the one that matched their records - of the tenant who was at work. The engineer then proceeded to go to the wrong street (not uncommon as the postcode isn't too accurate and the address is confusing). And as the tenant had their phone off due to the nature of their work, they couldn't get hold of me.
So after no-one has turned up for a while, I rang them back, to be told he'd been, there was no-one in, and he'd gone - and perhaps they'd be able to get someone back tomorrow. At which point I used "quite persuasive" language until they agreed to call the engineer and get him to return. The tenant had now got the message they'd left, and between us we managed to work out where the engineer was, walk down, and redirect him.
For good measure, he couldn't find any seals to reseal the cutout.

I know nothing about stage lighting, but my old school had an ampitheatre for an assembly hall, which was obviously used extensively for performances of all sorts. Control booth was above one side of the stage, looking out over the 'theatre' and stage. Not much more than a crawl space with all manner of equipment and accessed by ladder, but very cool for a school nonetheless.

 

[nicebutdim]