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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.
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.
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