3 phase explosion

[mark82jd]

A weird one but here we go.

I was asked to add a new 3ph circuit into an existing 6 way 3 phase dorma smith D.B. The board had to remain up and running ( not quite meeting the EAWR I know) so with the singles now in all I had to do was slide the 3ph breaker in the spare space 6L1-6L3.... This was where the explosion happened.

Everything was clear of the terminals, the new breaker was, just in case, switched off. As I pushed it onto the bare copper something caused 2 phases to come together resulting in me with temporary blindness, my hand completely black and ending up with me on the floor on the other side of the switch room.

The board and myself were in a bad way but once I was ok I began looking for explanations. The breaker wasn't bridged out which I had expected and nothing obvious stood out in the smoking D.B.
My foreman couldn't explain it either but he had heard of it happening before because of the air in a live board becoming 'ionized' therefore becoming conductive. Any spark caused by the breaker touching the busbar would have been enough to jump through the now conductive ionised air and bridge out to the next phase.

Has anyone else heard or come across this as I'm struggling to find a possible cause

Mark

 

[Geordie Spark]

I'm thinking that had it been me I wouldn't have dared tell anybody - never mind post it on a public forum, but there you go ... each to his own.

 

[malcolmsanford]

Well can't see where this "spark" would have come from without a load on it, and to be honest if there was a build up off anything be it 'ionization' or what, surely the cover would have been open and the air replaced.

No mate a more simpler explanation is that you somehow shorted the phases out. If your absolutely certain you never somehow went across them with a tool or something then for me a dodgy MCB with phases joined internally

 

[stef]

More than likely he pushed the busbars together whilst ' pushing the breaker in ', shame on his black piano fingers, him laying on the floor.

 

[mark82jd]

There is absolutely no chance the busbars pushed together, there was also nothing in my hand other than the breaker.
Are you guys seriously telling me you have never added a new breaker to a live board?? No established electrician around can say they have ever done this.

I have looked up ionisation and this seems plausable, just wanted to hear if this was possible....

 

[DurhamSparky]

again ionization will only happen under load...!!! so you eith had the breaker on with load or your telling porkies!!

the pics below are a true 3 phase explosion!

 

[Geordie Spark]

There is absolutely no chance the busbars pushed together, there was also nothing in my hand other than the breaker.
Are you guys seriously telling me you have never added a new breaker to a live board?? No established electrician around can say they have ever done this.

I have looked up ionisation and this seems plausable, just wanted to hear if this was possible....

Yes !! :yes: :smug: :vanish:

 

[stef]

There is absolutely no chance the busbars pushed together, there was also nothing in my hand other than the breaker.
Are you guys seriously telling me you have never added a new breaker to a live board?? No established electrician around can say they have ever done this.

I have looked up ionisation and this seems plausable, just wanted to hear if this was possible....

Frankly, no, I haven't. There is some sort a code of practise and a certainn H&S standard which I comply to, for the sake of my own and others well being. And no, no established sparky has ever done this. I once saw a training video when I was an apprentice ( decades ago) where a dummy via remote dropped a 17mm spanner into a 400A bus bar, the spanner vopurized in a fraction of a second, melting itself through the dummies visor burnt off the top layer of it's head, the bang it made is something I will never forget. So, no, I definately haven't.

 

[plugsandsparks]

The MG isobar boards are the only ones i would consider adding a breaker to whilst powered up. Some of the cheap stuff on the market is way to scary with all those prongs just sitting there waiting to grab you when you least expect it. No idea why it blew up but highly likely to be something directly across the busbars.
Even Sp Dbs are an accident waiting to happen simply adding a breaker for a shower etc.
Suggest put it down to experience, **** happens with this stuff , doesn't take much current really to make a melt down and we can get a bit blase about 40A ccts, 200Amp cicuits whatever

 

[Knobhead]

Ionised air degrades from O3 to O2 rapidly so it wouldn’t be present before work started. To create O3 either a high voltage corona discharge or a high energy arc is required.
You shorted the bus-bars, no ifs, no buts. Once the arc is struck O3 is generated propagating the growth of the arc.

Sorry to be blunt, you brought this on yourself. “The board had to remain up and running”. I’ll bet they had to manage without it afterwards.

I have looked up ionisation and this seems plausable, just wanted to hear

if this was possible....

Start looking for another excuse.
The HSE are going to have a field day with you, your boss, the company…….

 

[Guest123]

I have come across this before but only where the busbar bar connection prongs are of the fork type rather than one solid stub.

With a TP MCB, it is possible to get one half of the fork of one phase in the same connection terminal as one half of the fork of another phase, consequences are BOOM!


I've only ever known older ABB/wylex/crabtree DB's to have this fork style prong in them, not any other though.

 

[Guest123]

Similar to this.....

 

[Guest123]

Sorry to keep going on but, having had a think about it, Dorman Smith DB's do have this fork style arrangement in them also.

Believe it or not, it is quite easily done. I would be 99% certain this is what happened.

 

[Knobhead]

Qed . . . .

 

[Bobster]

Even in HV situations where I could hear the air ionising (winding ocbs back in). It would take a long time for a dangerous amount of O3 to build up, it turns back to O2 fairly quickly at sea level so I can't see the board being filled with it.

 

[Knobhead]

Why won't this board allow all capitalised words?

 

[DurhamSparky]

beacuse its a sign of shouting and been a hush hush, nancy pancy forum now shouting is banned...!

bit like plastic knives on aeroplanes!

 

[Guest123]

It's a rubbish File but, if you scroll down to "fitting and removal of MCB's" I think you'll catch my drift about the fork issue.

 

[Knobhead]

Well our OP has just looked back in. Didn't seem inclined to reply.

A question to the OP, "did you seriously think we would defend your actions?"

You took the chance!

 

[shagbite]

yep. dorman have twin pronged terminals and this bloke has definitely straddled two phases. i bet his ears are still ringing.

 

[ian.settle1]

A weird one but here we go.

I was asked to add a new 3ph circuit into an existing 6 way 3 phase dorma smith D.B. The board had to remain up and running ( not quite meeting the EAWR I know) so with the singles now in all I had to do was slide the 3ph breaker in the spare space 6L1-6L3.... This was where the explosion happened.

Everything was clear of the terminals, the new breaker was, just in case, switched off. As I pushed it onto the bare copper something caused 2 phases to come together resulting in me with temporary blindness, my hand completely black and ending up with me on the floor on the other side of the switch room.

The board and myself were in a bad way but once I was ok I began looking for explanations. The breaker wasn't bridged out which I had expected and nothing obvious stood out in the smoking D.B.
My foreman couldn't explain it either but he had heard of it happening before because of the air in a live board becoming 'ionized' therefore becoming conductive. Any spark caused by the breaker touching the busbar would have been enough to jump through the now conductive ionised air and bridge out to the next phase.

Has anyone else heard or come across this as I'm struggling to find a possible cause

Mark

Stupidity on your part for doing it live in the first place, if you worked for the company I work for you would have been sacked on the spot.

EAWR 14 comes to mind, if this was reported to the HSE expect to be making a visit to the man/lady with a white wig and black gown.

 

[johnboy6083]

I'm gona stick my neck out here and admit that I regularly terminate new circuits onto live DB's. 99% of the time it's MG/shnieder gear but sometimes it's square D. I would refuse to work on some DB's live, if I thought there was danger.
I know I'm taking a risk when doing this, and it's one that I accept. I'm always careful and I understand the risks. Unfortunately shutdowns in my industry are a nightmare to get, and often have to be at midnight for critical plant, which nearly all of the DB's I work on.
As for EAWR, it uses the term "as far as is reasonably practical". This is down to interpretation, and something that lawyers will argue about.
Im happier doing the above work than I am using old ACBs!

 

[Robotstar5]

All our boards are MG "isobar" and if I have to install an MCB live I still test the prongs even though the sliders are in the "off" position.

 

[Knobhead]

I'm gona stick my neck out here and admit that I regularly terminate new circuits onto live DB's. 99% of the time it's MG/shnieder gear but sometimes it's square D. I would refuse to work on some DB's live, if I thought there was danger.
I know I'm taking a risk when doing this, and it's one that I accept. I'm always careful and I understand the risks. Unfortunately shutdowns in my industry are a nightmare to get, and often have to be at midnight for critical plant, which nearly all of the DB's I work on.
As for EAWR, it uses the term "as far as is reasonably practical". This is down to interpretation, and something that lawyers will argue about.
Im happier doing the above work than I am using old ACBs!

There's a big difference between terminating a circuit and installing a new MCB, John.
I wouldn't dream of killing a board for connecting a cable.
OK they are a thing of the past but I'd happily conect to open frame boards live, but I was shown how to do it safely.

 

[Bobster]

OK they are a thing of the past but I'd happily conect to open frame boards live, but I was shown how to do it safely.

I had a very close call during my apprentiship with one of these boards.I should add, I wasn't working on the board I was cleaning in the sub.

 

[johnboy6083]

I include the fitting of MCBs in what I was describing Tony.
As I've said, I look at the job and make a decision on whether I feel I'm happy to do the job. The MG boards are brilliant bits if kit. I don't like SQ D cos I never feel like they make decent contact and they can arc a little of you knock em.

 

[Knobhead]

At the end of the day John we all know it's up to the electrician doing the job to call the shots. We’re each our own safety officer, never mind what “the management” think.
You’ve been in the game long enough to have influence on and the respect of the idiots that think they’re in charge. I’ll bet you’ve been in the same sticky situations as me where someone has had to put their foot down and say no. It doesn't make you the flavour of the month at the time, but no one can force the issue.
In the space of a week I’ve had a rollicking for working live and one for shutting a plant down. Just accept "you can't win" with them.

 

[Darkwood]

Working live!!! is how i wake up on a monday morning ..... nothing better than a good shock to prep you up for a hard week

 

[sparkdog]

Well I was going to fit a 3P MCB live but gone off the idea now.

 

[londonlec]

Anyone who says they have never fitted a breaker live obviously isn't employed by an agency, and definitely isn't a subby.

 

[Rockingit]

I think the bottom line is that we've all been there, to a greater or lesser extent. We've all exercised our own judgements on a situation, all done a job with one hand in our pocket....but those two comments contain 'judgement' and 'knowledge/experience'. It's not for the boys, just for those of us with a little grey hair. And the Electrical Trainee's can keep walking on past....nothing to see here.

 

[johnboy6083]

Ive got no grey hairs in my head thankyou! But I'm sure I will have at some point!

 

[Knobhead]

Even my beards gone grey! It's beyond the Greesian 2000 stage!

 

[mackers]

sorry to say i installed a tp mcb live on thursday please dont shout at me with big scary CAPITALS i also drilled the DB and made the swa off as well!!!

 

[Knobhead]

So you lived to tell the tale

Your not coming asking us to exonerate you for making a monumental bog up of the job.
As far as I'm concerned, I would be questioning the competence of an electrician not capable of installing a circuit to a board without causing major upheaval.
It's a part of being a competent tradesman.
View attachment 14733

 

[jeffducati]

what a Numty definate short says a lot for Merlin gerain boards i think they call it safe Isolation ???????????????
lucky man told the story many have not!!!!!!!!!!!!!

 

[Engineer54]

what a Numty definate short says a lot for Merlin gerain boards i think they call it safe Isolation ???????????????
lucky man told the story many have not!!!!!!!!!!!!!

Wit the MG isobar boards there is no chance of shorting two bars!! The board the OP was working on was a Dorman Smith board with exposed bars. You can't beat Schneider DB's, some may be equal, but never beaten.

Can you tell, that i like all things Schneider (MG)?? lol!!! That goes for both LV and MV equipment!!!

 

[Brightspark2]

I'm gona stick my neck out here and admit that I regularly terminate new circuits onto live DB's. 99% of the time it's MG/shnieder gear but sometimes it's square D. I would refuse to work on some DB's live, if I thought there was danger.
I know I'm taking a risk when doing this, and it's one that I accept. I'm always careful and I understand the risks. Unfortunately shutdowns in my industry are a nightmare to get, and often have to be at midnight for critical plant, which nearly all of the DB's I work on.
As for EAWR, it uses the term "as far as is reasonably practical". This is down to interpretation, and something that lawyers will argue about.
Im happier doing the above work than I am using old ACBs!

Ill echo this exact post.

That is all.:24: