Neutral to earth fault maybe?

[TedMosby]

Hey guys, I have a weird fault here with a kitchen circuit and could use some help with it.

Okay so I had a call out with someone saying there power was off in kitchen and first place I checked was the board(3 phase) and the obvious was a broke. RCBO and a loose burning neutral.

Before I changed the trip I checked round to see what was off and upon checking a socket with plug tester (socket switch & trip was off) plug tester came on and upon switching socket on it popped and tripped another RCBO off, switched back on and then carried on checking with that socket noted and came to the cooker, switched the electric hob on and the lights & socket (which were both switched off) had come on with the cooker hob. Even when the lights were switched on once u turned the hob on the lights would flicker like there double fed.

There was also a PIR sensor for the lights which had blown and cables in the fitting itself had melted( switching 28 50w GU10's & was 2KW rated) so anyone got any ideas? Lol I don't apart from neutral to earth fault which I'll be checking for in morning.

 

[sparkytim]

3 phase LOSS OF NUETRAL perhaps

What voltage are you getting? If 400 Volts at some outlets then this would go with a loss of Nuetral, and expalin damage.

 

[TedMosby]

Thanks for the reply, won't be able to check anything till tomorrow but I'll let ya know how it's going lol thanks again

 

[ProDave]

+1 to possible loss of neutral. Check each phase to neutral with a volt meter.

Otherwise, isolate ALL connections, L, N and E of each affected circuit and test each circuit thoroughly.

 

[sb_89]

Loss of neutral does Sound about right from what your saying, but if

Your getting 400v at one circuit it would be every circuit , as that would require the incoming neutral to be missing. It's not tncs is it ....lol

 

[sparkytim]

Not every circuit would receive 400 Volts just those on TWO of the phases.

 

[steptoe]

They Will, even those on single phase will have 400v possible backfeed on the N

 

[ProDave]

Sorry steps, I agree with tim on this one.

If the neutral is floating, then any rise on one phase MUST be accompanied by a drop in voltage on another phase. They can't ALL rise to 400V

 

[steptoe]

The phase wont rise Dave, the neutral will be the reference, no one phase can be 400v, it has to be referenced to something other than earth, ie another phase or neutral.

---------- Post Auto-Merged at 08:51 ---------- Previous post was made at 08:50 ----------

Like losing the neutral on single phase will rise it to 230

 

[sb_89]

+1

 

[TedMosby]

Thanks for the replies, just got to the job now gunna check for a lose/missing neutral now, and yeah it is tncs lol I'll keep you guys updated with some new questions on this which I'm sure I will have some soon lol thanks again

---------- Post Auto-Merged at 11:48 ---------- Previous post was made at 09:49 ----------

Hmm everything actually seems to be checking out fine now lol not getting 400v on anything Zi are giving around 0.50ish maybe it was just the loose neutral at the board was the cause? Checked over the appliances thy had blown and the fuses inside are all intact the boards are blown themselves so.., lol

 

[Evans Electric]

What exactly does lol mean ?

 

[Theorysparky]

laugh out loud text speak

or

lots of love ???? which some people think it is !!

 

[Andy™]

They Will, even those on single phase will have 400v possible backfeed on the N

i made this while back for a lost N on PME supply, but the basics are the same

 

[ProDave]

The phase wont rise Dave, the neutral will be the reference, no one phase can be 400v, it has to be referenced to something other than earth, ie another phase or neutral.---------- Post Auto-Merged at 08:51 ---------- Previous post was made at 08:50 ----------

Like losing the neutral on single phase will rise it to 230

Lets not split hairs, you know what i meant.

Yes the PHASES will remain correct, they won't go anywhere.

But the neutral, if it loses it's connection, will float and find it's own level depending on the phase balance. So it WILL rise towards the phase with the lowest impedance load on at any given time.

So in a single phase distribution system, the apparent phase to neutral voltage may go up or down, and it's perfectly possible to get 400V phase to neutral, and a lot of stuff going pop.

 

[sparkytim]

In my experiance on loss of Nuetral of a 3 PHASE supply 400 Volts is found present on circuits due to the coMmon nuetral connection at the DB effectively becoming a common point that puts TWO of the phases in series with each other hence 400 VOLTS between one phase at 230 v + at the same time as one of the other phases at 230 v -. The third phase is at 0 at that moment.

The result of this on one mobile home park when the supply Nuetral on A 3 PHASE distribution circuit feeding 9 Homes, 3 on each phase, went open circuit resulted in 6 Homes having damage, Boiler PCBs, Microwaves, TVs etc but 3 others with NO damage.

 

[steptoe]

Dave , I wasnt trying to split hairs, but I have come across this a few times where the N is at a scary potential,

in fact I was on a job a few years back on the IoM where we were changing a DB in a bank one Saturday night/Sunday morning and one of the sparks that was covering on the Sunday didnt realise all the N were disconnected and when asked by one of the temp staff to power up he did,

BANG!!!!!

23 PCs went pop,!

we measured almost 400v on that circuit N,

and no fuse to protect that sort of situation.