3 phase problem after spark did 5 year safety inspection

[jimthegent]

L2 in that three phase board loo from the electrical

No, definitely not.


The fault you show is of the top (input) of a single phase consumer unit. A 3phased balance load would not have any bearing on the fault IMHO.
The damaged cable is a 'red herring', I believe as the clamp being insulating material there would nothing to make a circuit and cause a 'short'.
I would think the DP Isolator has failed and there has been a L-N 'short' within the isolator, or maybe a stray strand!

The clamp is mild steel

 

[plugsandsparks]

Only going to know for sure with photos of the back of the clamp and back plate, if there are no marks i would agree and internal failure of the isolator comes into play, then was it caused by a loose connection or an internal failure of the DP Isolator. I saw the split in the tail on L2 supply and blamed the clamp (until proven otherwise) - it possible the heat generated by a loose connection compromised the tail insulation, hence you would need to see the components to work out what went first.
However i think we all agree unless the CB in the TP board is welded shut, then ADS should have saved it from this mess if it was indeed overload. (assuming the SP board is fed from the TP board) - i cannot tell from pic

 

[jimthegent]

L2 in that three phase board looks like its got hot too?

Could that have come from the electrical fire in the box we had it was cleaned up but initially there was a load of soot and detritus all over the box

 

[plugsandsparks]

I cannot see a SP breaker in the TP board to feed the SP board, so do the tails go to the Henleys and then straight to the incoming fuse? - If so i assume (again) this is either a 80A or 100A TP supply?

 

[jimthegent]

Only going to know for sure with photos of the back of the clamp and back plate, if there are no marks i would agree and internal failure of the isolator comes into play, then was it caused by a loose connection or an internal failure of the DP Isolator. I saw the split in the tail on L2 supply and blamed the clamp (until proven otherwise) - it possible the heat generated by a loose connection compromised the tail insulation, hence you would need to see the components to work out what went first.
However i think we all agree unless the CB in the TP board is welded shut, then ADS should have saved it from this mess if it was indeed overload. (assuming the SP board is fed from the TP board) - i cannot tell from pic

Only going to know for sure with photos of the back of the clamp and back plate, if there are no marks i would agree and internal failure of the isolator comes into play, then was it caused by a loose connection or an internal failure of the DP Isolator. I saw the split in the tail on L2 supply and blamed the clamp (until proven otherwise) - it possible the heat generated by a loose connection compromised the tail insulation, hence you would need to see the components to work out what went first.
However i think we all agree unless the CB in the TP board is welded shut, then ADS should have saved it from this mess if it was indeed overload. (assuming the SP board is fed from the TP board) - i cannot tell from pic

We are never going to know that the contractor returned the next day replaced the breaker replaced the burnt out tail and clean the crime scene up they also removed the items which technically still belong to us

 

[plugsandsparks]

OK, but your loads presumably have not changed prior to now, so just measure the load now.
A pic of the SP board breakers may give a clue to whether overloading the board is even possible.

It was rather naughty to not leave the isolator with you, however you still have the board and clamp. ;-)

 

[jimthegent]

OK, but your loads presumably have not changed prior to now, so just measure the load now.
A pic of the SP board breakers may give a clue to whether overloading the board is even possible.

It was rather naughty to not leave the isolator with you, however you still have the board and clamp. ;-)

They probably

 

[MJPD29]

Yes the cover of the board was blown off and there's a lot of black soot all over the switches so clearly a lot of heat was generated

The cover was blown off? Really?

 

[MFS Electrical]

Yes 100% he took them out and put them back in again

Certainly not a standard thing to do on an inspection.

When you do the 2391 (inspection and testing) you are told to disturb as little connections as possible to ensure you don’t create faults.

It’s highly unlikely that the electrician would have removed the tails and reterminated them on an EICR (inspection)

Also, the picture you’ve posted looks like a single phase main switch?

 

[MFS Electrical]

An overloaded board but it's run fine for 5 years and it just happend to blow a few hours after they wiggled the wires plus each phase is perfectly balanced with 9 feeds

So he didn’t remove the tails? But wiggled them?
Sounds more likely that there’s been a problem hiding there for a while either from a loose connection causing the cable to overheat and eventually melt into the clamp or the wiggle has exacerbated a defect already there and with a little load on the cable the cable moves and boom.

Also re the overload; It is certainly possible that an overload has occurred even if it has been running fine for years. An overload of a small magnitude can be enough to heat the cable past its operating temperature and cause it to significantly expand, then upon cooling and contracting loosen the connection. Rinse and repeat for 5 years and you certainly could have a situation like this.

I see it all the time where a shower installed on a 6mm cable ran through insulation in a wall and then under loft insulation is used to power a 9.5kW shower and due to the overloading of the cable (which should have been derated due to the insulation) burns out at the terminations of the switch or the MCB or the shower.
Genuinely, funnily enough it usually takes around 5 or so years of normal use for the problem to come to light by which time the spark that put it in is long gone.