Arc me up........................

B

Bobster

• Aug 20, 2014

• #2

I wouldn't have said condensation alone would cause an arc like that. Especially in an LV board.

 

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a1guvner

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• Aug 20, 2014

• #3

RoB2 said:

I wouldn't have said condensation alone would cause an arc like that. Especially in an LV board.

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It was a very strange one to try and prove, at fist i thought maybe the caretaker having a fiddle with something he shouldnt but the flash marks are in the inside of the door proving it happened whilst closed,

 

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B

Bobster

• Aug 20, 2014

• #4

I would have maybe said something loose inside the panel, finally moved due to vibration or similar. You'll struggle to melt copper like that without a direct short.

 

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G

Guest112

• Aug 20, 2014

• #5

shame as the install as a whole looks a good quality lol

 

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a1guvner

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• Aug 20, 2014

• #6

RoB2 said:

I would have maybe said something loose inside the panel, finally moved due to vibration or similar. You'll struggle to melt copper like that without a direct short.

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i thought that at first, when you look at the Mcb those prongs have a plastic cover over them and these were still in place apart from the centre cover had come loose after the fault along with the fact it being the second way down makes it even stranger.

 

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RogertheBodger

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• Aug 20, 2014

• #7

Had a fault like that once, perplexing. Turned out to a split shroud on a SWA supplying an A/C unit outside on the roof, the water was getting in and making it's way down through the armoring and core gaps into the panel, Took some finding luckily I was called back to it when it was raining, worth a look. Good luck.

 

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Tiny Spark

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• Aug 20, 2014

• #8

As all the burning appears to be down the middle was there anything that could of shorted between the front and the terminals?

 

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a1guvner

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• Aug 20, 2014

• #9

Tiny Spark said:

As all the burning appears to be down the middle was there anything that could of shorted between the front and the terminals?

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Hi, there was nothing that could of shorted at all, clipped in nice and tight, only one of the covers had come loose and the others were still intact and secure, the busbars on the gear tray were still nice and clean

 

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A

ayjay

• Aug 20, 2014

• #10

looks an expensive repair and once done it might just do it again
there is some rust showing on the cabinet

 

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a1guvner

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• Aug 20, 2014

• #11

ayjay said:

looks an expensive repair and once done it might just do it again
there is some rust showing on the cabinet

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Yes it is in a hot plant room, there is some passive ventilation system which i dont really know much about, when we changed the DB we advised the client to check with the installer of the ventilation system, there is a large slatted grill in the plant room wall opposite this DB but about 4 metres away

 

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D

Darkwood

• Aug 20, 2014

• #12

What temp' is normal running ... does the room drop temp' fast when work shift has finished.... this is strong evidence of cold air condensation on the the warm mcb ... I get this often in old panels that run all day and at night the temp' drops like a stone, all the contactors etc get soaked in droplets ... once the arcing starts it creates a runaway reaction as it burns and changes to carbon the plastics etc which is a conductor ...which in turn allows more current ..etc etc etc ..


If your are adamant nothing has leaked down the back of the board through the busbar lines from an external source then condensation is your culprit.

Where is the air coming from that is venting through the room ...is it dried or straight from outside... if the later then a redesign of your ventilation as well as preventative measures for condensation need installing.

Ive had this issue many times under totally differing set up from a DC motor been cooled with external air which condensed in the steel venting and filled the motor up with water, to as mentioned before panels and DB's.

Ive seen paxolin shields and separators become conductors because of this effect Ill dig the pic up if I can.

 

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D

Darkwood

• Aug 20, 2014

• #13

RoB2 said:

I would have maybe said something loose inside the panel, finally moved due to vibration or similar. You'll struggle to melt copper like that without a direct short.

Click to expand...

Condensation can do this easily it carbonises the materials it tracks over and even deposits vapourised copper layer (check his pick of the rear of the cover).. once this happens the current increases and like mentioned in my previous post - it becomes a runaway effect until bang!!!!

This is from water ingress ..a drip in this case onto the busbar that ran across the paxolin to another busbar..the 2 bolts in pic 2 were bolted to adjacent phases hence the tracking from one to the other.



Note the repair was a temp' fix the whole lot has been upgraded since.

 

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Lucien Nunes

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• Aug 20, 2014

• #14

Agreeing with all the above, it could well have started with moisture although the room doesn't look like it suffers from rampant condensation so I quite like the water-seeping-through-armoured theory. But something strikes me as odd, if it was caused by moisture. As in DW's pic, the insulation tracks and chars, self-heats and eventually starts a flashover, but by that time it's usually already black and crispy.

In your board, where the power arcing has occurred at the outer end of the busbar clips, the MCB case material is still very much intact. Most of the black deposits seem to be a result of the splash rather than charring of the plastic itself, i.e. there doesn't seem like enough damaged plastic to trigger a full-scale arc. I have to wonder whether there wasn't a wire trimming or something trapped behind the MCBs? Of course the arc might have started in the busbar pack and blown itself towards the outer ends of the clips but it still doesn't feel like the full story.

 

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D

Darkwood

• Aug 20, 2014

• #15

His second set of pics clearly show water has dripped down and caused rust, this is a newish clean install, if the air is been vented in from outside during the colder nights after a moist warm day you will be surprised how much condenses, like you say unless we are not privvy to some crucial info then I'll edge my bets its mostly occurred in spring with warm days and cold nights and again over the last week as night time temp's can be 10-15 degrees down on the day time and it drop very quick.

Where is this job is it in the sticks where air temps are getting close to frost over last week?
Any further info on the venting system too?

As for the SWA theory Nunes - they all come up-hill the conduit in the top is the only possible culprit but would be evident on the cables in it.

 

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