Is this bad?

[Paul.M]

 

[JD6400]

Now correct me if i am wrong but if this is a PME supply and this is the main board if you had lost the neutral your looking at mains potential earth bonds and metal work , especially if someone else had been a little slap happy on earthing arrangement .
And if it was a three phase installation earthing in place or not you would be looking at maybe 5-600 volts down one phase !
I have seen both scenarios and neither is good mojo , not having a go but if in doubt phone a Friend just to confirm your thoughts before you leave next time cause i think you may just have used up one of your life's , get out of jail free tokens.

 

[nickblake]

no because it needs the path from the cutout if you lost the neutral before the neutral / earth link at the cut out then yes you would and on three phase with the neutral missing you then have a potential 400 volts across light fittings etc however as i have stated in my post any neutral to earth shorts then this will back feed down to the earth bar and on to every earthed appliance potentially sticking volts on the earthed appliances , but as the supply is tied to earth where the neutral to earth fault is is where the whole installtion would run off and could possibly cause problems

 

[JD6400]

no because it needs the path from the cutout if you lost the neutral before the neutral / earth link at the cut out then yes you would and on three phase with the neutral missing you then have a potential 400 volts across light fittings etc however as i have stated in my post any neutral to earth shorts then this will back feed down to the earth bar and on to every earthed appliance potentially sticking volts on the earthed appliances , but as the supply is tied to earth where the neutral to earth fault is is where the whole installation would run off and could possibly cause problems

Hi Nick
Like i say i am open to correction , but you will get more than 400v .
We had one last year on a new supply , the meter installer had forgot to tighten the screws on the neutral load side of his meter and it as good as dropped out . We had 3 / 9kw 3ph electric boilers on it and it melted all the controls in them ( i think overall cost of around £ 17,000 ) but we were getting from 50 v to i am pretty sure 580v phase to earth .
I was only talking to a chap from UK Power Networks who installed the monitoring gear on one of our larger solar jobs on Wednesday morn about this and he confirmed this is not uncommon when there is a lost neutral on a three phase , he did explain the theory how but it was a little lost on me .

 

[JD6400]

Sorry Nick i forgot to say that i have reread op and paid little more attention this time and you are right on the PME bit .

 

[baldsparkies]

Saw the results of a loose neutral on a temp genny supply to an office block by the DNO.
Lots of fried single phase equipment.
The DNO operatives told us they have to pay for the damage because its such a common occurence they cant get insurance companies to under wright them !!!

 

[nickblake]

With a lost neutral on three phase that is befor the cut out there is literally no where for it to go so as what happens is you have say L 1 and L2 L3 through the MCB to the circuit and back to the common denominator which is the neutral bar , now due to their being a resistance across loads on the circuits it then back feeds up the phases blowing up any HF ballasts in circuit and due to the designe of switch starts they try and start up hence the flickering lights , also when this happens any earthed or extrainiouse parts that are bonded become live , one of the most common signes for a lost neutral is when you test across live and earth you will get a reading of around 120 volts and if you have a metal clad dist board its out with the gloves lol this problem occoures in TNCS systems hence there are lots of area's where TNCS systems are not permitted IE caravan hook ups so its intresting