bizarre fault

[siroccomanuk]

Hi, come across a fault this evening. Split load board, lights on non rcd, sockets rcd side. If anything gets plugged in to the sockets circuits and switched on (3 seperate rings) the voltage drops to 120 across all circuits. Also seem to be a bit of back volts down the earth. Have not had time to have a good look, so left them safe with lights only until the morning,

Any advice / help / clues as to where to look would be great.

Dave

 

[flameport]

Tails loose or hanging out most likely. Either in the CU or cutout.

 

[siroccomanuk]

Nope - that was my first check they are tight. Undid them and re tightened to maked sure.

 

[Spark123]

With the fault present, what are the phase - neutral, phase - earth and neutral - earth voltages?
What supply type?
Im thinking there may be a bad connection upstream of the consumer unit on the neutral side, hence the possibility of the neutral being raised to 120v above earth as opposed to the earth becoming live.

 

[Lectrician]

High resistance neutral in the supply to the property sounds the likely cause.

 

[siroccomanuk]

With the fault present, what are the phase - neutral, phase - earth and neutral - earth voltages?
What supply type?
Im thinking there may be a bad connection upstream of the consumer unit on the neutral side, hence the possibility of the neutral being raised to 120v above earth as opposed to the earth becoming live.

phase 205
neutral 205
earth 50
tncs

fault just suddenly occured while occupier was out

 

[securespark]

Have you got any neutrals connected to the earth terminal?

See this thread: http://www.diynot.com/forums/viewtopic.php?t=156922&postdays=0&postorder=asc&start=0

 

[securespark]

Also, what is the Ze?

 

[flameport]

What type of supply is it?

If TT, perhaps one of the neighbours has done a DIY conversion to TNCS and got it wrong.

 

[siroccomanuk]

doesnt seem to be any neutrals misplaced.

ze: 0.32

 

[securespark]

If everything is tight in the CU, then it could well be a suspect neutral connection prior to the CU, as others have suggested.

Have you asked the DNO to inspect?

 

[siroccomanuk]

Well, yes DNO was asked to investigate, and got the standard response, nothing wrong with our supply sir. Going back tomorrow to have a look in daylight.
Really thrown me this one 26 years of being a sparx and totally baffled

 

[securespark]

What did they actually do?

Did they open up the cut-out and meter to inspect their connections?

If not, then I would have them back to inspect their side as they need to eliminate it from the equation. Explain you have examined your side of the installation and all apears well, but the symptoms you're getting point to a high-resistance neutral that, under load, drops shed-loads of voltage.

As for voltage, is the supply voltage L-N 205V when the installation is not under load and 120V when under load?

If so, the supply voltage is out of tolerance and that needs looking at. Insist the DNO return when you're there & explain all to the engineer. Butter him up a bit with T & bix if necessary!

 

[siroccomanuk]

sorry, should have read 225 NOT 205 when nothing on

120 when anything on

 

[ColJack]

phase 205
neutral 205
earth 50
tncs

fault just suddenly occured while occupier was out

I'm confused..

Phase to what is 205
Neutral to what is 205
and more to the point, Earth to what is 50v?

that looks like a dodgy earth if those are "to earth" voltages..

that's 255V to true earth with the installation earth at 50V above true earth?


205 to earth indicates it's not a TN system..

the 120 under load also sounds like a center tapped transformer with a dodgy side to it.. leaving you with 120ish to earth on one side..