Power surge and fire

[nickblake]

How the hell can you prevent this , got a call from a hair salon saying the lights have flickered and gone off and weve lost the power and there a smell of burning got there 3 RCBO's tripped ,switched off ,whipped off cover of CDU all looked ok so quick Ze 0.71 tad high for TNCS , so quick voltage test 291 volts mmm very high me thinks , so popped round to the garage a few doors away who appeared to be in darkness to find there had been a massive power surge setting fire to the incomming supply , credit to the quick thinking guys with a fire extinguisher who put the fire out within seconds , garage forcourt very lucky

 

[topquark]

Could have been very nasty especially if the forecourt was fuel dispensing. Bring on the SPD's, I assume that would have offered some protection.

 

[bugsy]

Power surge arresters

 

[nickblake]

Just an update found out the cause , a lost neutral ,so scottish power say shop i was in has 14 blown HF ballasts blown phone blown radio all CFL lamps blown tests out ok ... some lost neutral garage opened again at 4 today and pub not opening for a while

 

[telectrix]

Just an update found out the cause , a lost neutral ,so scottish power say shop i was in has 14 blown HF ballasts blown phone blown radio all CFL lamps blown tests out ok ... some lost neutral garage opened again at 4 today and pub not opening for a while

now that could be a disaster if there's not another pub for miles.

 

[nickblake]

From there its a good 15 minuit walk to the next one , 2 1/2 hours back mind

 

[LlandrilloSpark]

Where was it nick I've been in Holyhead all week, anywhere close?

 

[nickblake]

Pentraeth ,very scary stuff if it had happened at night i dread to think of the consiquences , unbelivable how much damage a lost neutral can cause , ive never seen so many scottish power guys and there big wigs there must have been 8 walking round with clip boards and very clean hi vis and hard hats

 

[malcolmsanford]

Nick was this a lost neutral on the PME due to joint/cable failure or someone nicking cable from a sub mate

 

[nickblake]

It was a lost neutral on a PME cable joint underground ,no cables above ground transformer on the pole , ive seen loads of lost neutrals over the years but never one to set Fire and melt meters , the fault current must have been incredible ,i was told it was a neutral fault by scottish power guys , but when i was on site the ze readings were high ish 0.71 PME but the voltage was 291 volts , lost 6 out of 12 hf light fitting the other works but for how long im not sure that sort of voltage must have damaged them ,

 

[Guest123]

Diverted neutral current & petrol stations.......could have been really really bad if things werent quite as they should have been!!!:disguise:

 

[keniff]

What causes the supply's to melt and get a higher voltage reading from a lost neutral? Iv seen loose neutrals on a domestic supply loose and start heating up and melting, I just can't get my head around whats happened here

 

[malcolmsanford]

Keith because the area will be supplied from the sub in 3 phases. In a typical street you will have a 3 phase supply with houses split over the 3 phases. So you next door house may be a different phase to yours.
If you loose the neutral completely you will have a situation of "floating" and could get 2 phase now at your head, so instead of the 230 of LIVE/NEUTRAL you will get 400v PHASE/PHASE and so have what Nick discovered.
With Nick getting 291 votls at the installation it would not have been a total neutral loss but a breakdown/fault.

 

[nickblake]

If you take a lost neutral on a PME system where the earth is connected to neutral at the cut out then neutral then looks for a Path the common connector is the neutral bar so with loads in line these cause a resistance and the lives from the other phases back feed up these lines hence anything upto 400 volts blowing up any sensitive fittings in line on domestic if this happens you can get an increase in current as lenny has said diverted current it can cause incredible damage as has been seen , another scenario on a PME system is if you loose the neutral before the supply enters a premisis it then back feeds down the neutral to the connection for the earth then down the earth connection to every thing thats bonded appling a nice 120 volts on all metal objects , this is part of the reason why TNCS/PME systems are not permitted on caravan parks

 

[Knobhead]

The phase to failed neutral voltage is dependant on the loading across the 3 phases. If all phases are in balance then there will be no shift in voltages. But say the phases are out of balance the phase with the lowest loading gets a higher voltage as the phase vectors shift. It’s not an easy thing to follow.