Bit of a mystery to me, any ideas? Fault on three phase Merlin Gerin

[Vortigern]

Outage of main three phase primary switch box for one of three buildings on commercial site. The building houses around 30 commercial units. Switched back on the main switch, power restored. Except for one unit. All units supplied through the secondary sub switch box. Large MCCB MEM type.

Three phase and single phase off to units. The unit that did not switch back on was a three phase unit, sub main, Merlin Gerin TP+N. All single MCBs to ring circuits and lighting. Nothing unusual power wise just an office been there since 1992. Took off cover of DB and found the central spine the MCBs attach to showed signs of a short or major blow out.

I enclose pictures of the interior of that spine/bus bars with the top removed to examine the short. Only problem is there was not a short. You can see the carbonisation. The MCBs were not damaged at all. There were no foreign objects or loose parts yet there must have been an arc over or something. People in office said they heard a bang. They were doing nothing out of the ordinary. There were no vaporised metal parts.

The upstream supply at the MEM MCCB had popped off. I put it on and put the spine/bus bar together and switched on Merlin DB without load. Progressively switched on each circuit, waited an hour or so, nothing, everything worked fine. Zs at all sockets as the epi center of the carbonisation was on the 32a MCB. Zs was fine for all circuits. 3 rings radial/3 lights/other 7 in all.

Any thoughts? a million to one chance of a massive surge at that box across phases???? Never seen this before and I have dealt with a lot of Merlin Gerin. Sorry about the picture quality but at least it gives an idea of what I am talking about. Gonna change the box but just curious as to the why.

 

[Vortigern]

The third picture is of the sliders you get with Merlin Gerin bus bars to disconnect the power from the live tang. Could be an arc from one of these, but still, why.

 

[Lucien Nunes]

Pretty certain there was something in there that shouldn't have been there. Whether debris from installation that happened to move, or something that walked in there by itself. Probably something non-metallic if there's no localised splash anywhere on the bars. Unlikely to be surge-related on a submain, if nothing else in the installation is even slightly damaged.

 

[Vortigern]

I took it apart on a table that was clear and examined carefully each component. There was nothing floating around or stuck on any component of it. No vapourisation of any of the metal parts at all. All compartments were intact i.e. the plastic separating the the bus bars for each phase. I guess the distance between the phase bars must be at least 10mm. However I take some comfort that you @Lucien Nunes do not immediately see what the problem might be.

 

[UNG]

I think I would be passing it to Schneider for comment, there is clearly an issue to cause the failure and the question that has to be asked is this an isolated incident or are there other boards in service that could suffer a similar failure

 

[Vortigern]

I think I would be passing it to Schneider

That is a very good idea, will action that ASAP. Just emailed uk support.

 

[Vortigern]

I thought, well that post sunk like a stone. However a couple of you have rallied and come up with some pointers, always appreciated. Also good to bounce it off others to make sure I am not missing something blindingly obvious.

 

[Vortigern]

Here is a picture of the three phase bus bar chamber before taking apart that shows the carbonisation. My expectation was to find melted metal parts, but none were found. I might buy the idea that a foreign object such as fauna was abroad in the chamber and got vapourised.

 

[Rockingit]

Spider?? Not as daft as it sounds

 

[James]

Spider?? Not as daft as it sounds

I thought spider possibly built a web as well

 

[Vortigern]

Anyway, sent pics today and spoke to Schneider tech. They are as stumped as me/us? But even so they are willing to take a look. When I put the new Hager Invicta board in I will send the actual bus bar chamber to them. But the tech guy said it is impossible, never heard of it there is nothing could go wrong and the first time he has ever heard of this, me too. Bit of a mystery then, maybe we will never know.

 

[Wilko]

Hi - sorry to hear of your troubles V !
I had a look at the pics and my 20p is something was vaporised in there, I can almost see it’s shadow, ha ha.

 

[ipf]

Pretty certain there was something in there that shouldn't have been there. Whether debris from installation that happened to move, or something that walked in there by itself. Probably something non-metallic if there's no localised splash anywhere on the bars. Unlikely to be surge-related on a submain, if nothing else in the installation is even slightly damaged.

Once had a 3ph board supply shorted by a slug. Holding onto a live bar connection and stretching out to reach the DB casing... we deduced.... it was splattered all over.

 

[Vortigern]

You might be on to something there. When I put in the invicta board I will relook at that @Wilko

 

[ipf]

Once had a 3ph board supply shorted by a slug. Holding onto a live bar connection and stretching out to reach the DB casing... we deduced.... it was splattered all over.

Found these.

 

[Vortigern]

Yukky!