Supposed Fault On Merlin Gerin Dis Board

[R G]

Hi All,
Here's a new one , has anybody heard of a Merlin Gerin 3 phase dis board self destructing , the story goes that the Electrician working on it had a phase to phase short within the central enclosure ie between the bus bars , this is the story I was told about , I must admit I and many others find hard to believe , the consequences are that 2 x supply fuses were taken out and caused an allmighty explosion when the front cover was re fitted

 

[pete555]

Hi All,
Here's a new one , has anybody heard of a Merlin Gerin 3 phase dis board self destructing , the story goes that the Electrician working on it had a phase to phase short within the central enclosure ie between the bus bars , this is the story I was told about , I must admit I and many others find hard to believe , the consequences are that 2 x supply fuses were taken out and caused an allmighty explosion when the front cover was re fitted

there must be more info for this i work alot on merlin boards so would be interesting to know all details

 

[Jonny66]

Hi All,
Here's a new one , has anybody heard of a Merlin Gerin 3 phase dis board self destructing , the story goes that the Electrician working on it had a phase to phase short within the central enclosure ie between the bus bars , this is the story I was told about , I must admit I and many others find hard to believe , the consequences are that 2 x supply fuses were taken out and caused an allmighty explosion when the front cover was re fitted

You've got to be kidding, a self destructing DB, what would be the point? unless the spark wasnt qualified...I beleive Merlin Gerin DBs will explode if they detect an NVQ3.....

 

[R G]

More info
I was also told that the dis board is the type with with the MCB lock off switches and that the fault was suposedly within the switch mechanism , I have never known it ,but there we are , apparently it took the shop out off trading for the next day

 

[pete555]

More info
I was also told that the dis board is the type with with the MCB lock off switches and that the fault was suposedly within the switch mechanism , I have never known it ,but there we are , apparently it took the shop out off trading for the next day

it appears to be a dead short some how but i would have thought that that amount of damage would have been caused by all three phases shorting but did you say 2 phases had there fuses pulled

 

[R G]

The info I got was that 2 HRC fuses had blown that supply the board

 

[pete555]

The info I got was that 2 HRC fuses had blown that supply the board

need to think about this one

 

[Jonny66]

If you had a "close up' fault/short between phases you would be talking about alot of fault current .....and if greater than short circuit capacity of MCB then I would imagine there could be a bit of an explosion...but with the fuses you would have some form of back up protection and it would be down to let through energy of these fuses.....but if it was a direct short at the MCB I dont think you would of got to the stage of closing the DB door......

 

[diditrain]

I think that you need to know what the Electrician was there to do in the first place. This may give some clues as to what went wrong.

 

[KAS1]

How long ago did this happen and did the electrician get hurt?

 

[R G]

I would like to have seen the Dis Board myself , and made my own judgement, but there you go , when I spoke to him he was shook up about it but was not injured , so thats something I suppose

 

[ufkir]

installed only when you know youve got a non paying customer

 

[guest119]

Only probs I have heard of (twice) was when an extension section was added for an mccb instead of the 125a isolator.
125a isolator will only take up to and inc 50mm. cable.
A long run from incomer may set the supply cable at 70mm etc so an mccb or larger isolator and extension would be req.
There are 5mm allen head screws holding the bus bar replacement stubs and if overtightened they will break............later, causing havoc with a decent load. IE catering etc.

Boydy

 

[R G]

Thanks for All replies lads,
It makes me more skeptical as to what really happened , the work being carried out is a simple alteration to an existing circuit , no alterations to the MCBs already in the board

 

[shocking_eg]

probably a load of swarf inside the busbar chambers... been disturbed when pushing covers on etc...

been there done that !

it happens quite easily !

 

[mark ju]

Did it involve perhaps the use of a holesaw on the top plate of the DB? Only ask as i know someone who killed a board in a hospital by letting the piece from inside the holesaw drop down inside. Careless!
Obviously he had not isolated the board.
Story also goes that he actually s##t himself!

 

[guest119]

That is why I have Q Max cutters in my kit.
20mm, 25mm, 32mm, 40mm, 51mm, very cheap on E Blag.


Boydy

 

[JD6400]

Did it involve perhaps the use of a holesaw on the top plate of the DB? Only ask as i know someone who killed a board in a hospital by letting the piece from inside the holesaw drop down inside. Careless!
Obviously he had not isolated the board.
Story also goes that he actually s##t himself!

I just love that last line !:willy_nilly:

 

[Darkwood]

The early generation of merlin D-boards were similar to modern but with a big flaw the busbar link from the main switch to the main central busbar rise were exposed on the rear but not on the front... now if you passed a exposed copper wire across the space behind the busbar riser(a unsleeved earth wire) you could short out the incoming links and if it had a standard main switch as oppose to a mccb and the front end was the DNO fuses then it can set the main switch into a firework display and take out the incoming....

I see so many comments saying it a load of bull but try not to give a focused opinion if your experience in the industry isn't long try sit back and learn from the more established members ....we dont know everything but we can enlighten you to things you never realised.

 

[R G]

Hi All
Thanks all for the response , as I said I would like to have seen the dis board and quite possibly come up with the same conclusions , but it seems it would be great for all of us to be aware of this situation , just in case we come across it .
Many Thanks All Ray Galea

 

[Robotstar5]

and today I was telling my new boss how good MG isobar boards were!, will I have to retract the statement tomorrow?

 

[Darkwood]

It only effects the older generation boards as they quickly realised the dangers that exist with the unseen exposed busbars modern boards are fully insulated or inaccessable even at the space behind the switch and busbar system.... remember most sparkies were passing wires down the back when adding new circuits and those who are unaware might put their hand behind or push a bare earth across as i believe has happened in the OP mates case.