11-12 volts reading across line and earth

[Sting Ray]

trying to trace an earth fault in a friends home today after the RCD in the single ring main suddenly and persistently started tripping
why might I see 11 to 12 volts across line and earth on some sockets?
are there any tips regarding finding the earth fault? have broken the ring and disconnected all sockets and i am working my way along the ring reconnecting one socket at a time until the fault reappears

 

[Sting Ray]

Okay the way I read this is you're actually worrying about two different faults here. Firstly there's the low insulation that was causing the RCD to trip. Secondly there's a mysterious 11-12 volts appearing at some sockets between the L and E.

Just ignore the 11-12 volts between the L&E, chances are it's a meaningless reading because you're using a tester with an extremely high input impedance which is over sensitive. Concentrate on finding the extremely low insulation problem between N and E.

Just to close this one, fault traced to part of ring next to boiler, cables buried in wall and also in inaccessible ceiling void. Broke ring at nearest reasonable point and remade ring with those lovely Wago connectors, like taking out a bit of bowel. All good except boiler now needs new permanent supply rather than the extension lead from a nearby socket. Also found many sockets with green goo, I know what that is now but the client doesn't want to consider a rewire just yet. Ring is a ring, insulation >999MOhms, happy days. Thanks

 

[Octopus]

Where has this trend for measuring voltage to do fault finding come from ?

I have noticed quite a lot of fault finding questions being posted, real,induced and phantom voltages are noted, then used to try and trace insulation and continuity problems
Does the training reflect this method these days or is it just the "in" thing to do this

No idea, but switching off other circuits normally clears it!

 

[guest119]

socket. Also found many sockets with green goo, I

Yellow 77 gone septic?? :yesnod: (Google it)


Boydy

 

[Marvo]

Just to close this one, ........ insulation >999MOhms, happy days. Thanks

Glad to hear you got it sorted out.

Where has this trend for measuring voltage to do fault finding come from ?

I was also thinking the same thing a few days ago. It's a poor way to localise a fault and it causes a lot of confusion with the digital testers nowadays which are way over-sensitive. I hope to hell they're not teaching this method on the courses.

 

[Silly Sausage]

Where has this trend for measuring voltage to do fault finding come from ?

I reckon that it's just people checking a circuit is de-energised, then getting confused by 'false' readings.
Henceforth, Lo-Z voltmeters to be issued as standard.

 

[Marvo]

I'm surprised how few sparkies carry an analogue voltmeter nowadays, I'd say it's as much an essential piece of kit as it ever was. Digital testers are great for some things but the fact they're way over sensitive for many general applications coupled with the lack of understanding of how attributes such as their input impedance and burden affects the results you see and regularly causes chaos.

 

[Dizzy_Maskell]

Something's gotta be the new fad might as well be this

 

[Sting Ray]

socket. Also found many sockets with green goo, I

Yellow 77 gone septic?? :yesnod: (Google it)


Boydy

no, try di-octyl phthalate, the substance is coming from inside the outer sheath, those nice people some 50 years ago have created a job for electricians today and tomorrow

 

[spynage]

Whats this yellow 77 gone septic. I googled and got septic tanks..

 

[Des 56]

https://www.google.co.uk/#q=yellow+77&tbm=shop&spd=7464261282142941541