Live earth conductor

[JD Hogg]

Yesterday I was installing some downlighters in a bathroom, I isolated the supply tested L-N and it was dead, grabbed hold of the choc block which was used for the existing light, stuck my screwdriver in and got an electric shock. That was weird so tested again and it was still dead so I thought it must be some lighting control gear holding a charge, so carried on and got another electric shock so got my voltmeter and measured 240v L-E and N-E. I tested various circuits and the earth was live on all of them (as you would expect), all pipework was live and even the shower cubicle was live.

The house is in the country with TT earthing and recently installed PV system which I know nothing about.

I immediately suspected the PV system and switch off the AC isolator to it which removed the voltage from the earth.

A while later I went to try to find the cause of the problem and switched the isolator back on, checked the PV was generating but no voltage on the earth.

Tested the Ze which was 65 ohms which is OK.

Does anyone have any ideas as to what could have been the cause of the live earth and why nothing tripped out?

And yes in future I will test L-E and N-E as well.

 

[steveberry11]

What did you use for your first two tests prior to getting the volt meter out.

 

[londonlec]

Incorrect polarity issue at the PV somewhere?

- - - Updated - - -

Was there an RCD somewhere? (and does it trip at correct times?)

 

[JD Hogg]

The house wiring is unnecessarily complex, 6 distribution boards, tons of X10 home automation, all circuits are protected by RCBO's but none of them have tripped.

 

[Moses]

The house wiring is unnecessarily complex, 6 distribution boards, tons of X10 home automation, all circuits are protected by RCBO's but none of them have tripped.

You need to start from the start!

Are there and PIR/EIC ?

If not, you need to do an EICR.

Check all circuits for, R1+R2, IR tests

Test all RCBO trip times,

 

[Darkwood]

L/N test only ..... not supprised you got a shock, always do a full test with correct tester... L/N, L/E and N/E.

A wiring issue or fault may be missed if you dont!!

But i see you already noted that but this occasion you were lucky it wasn't anything more serious than a shock.

If you did this in an exam condition you would have failed for good reason......

But preaching aside --- i under the impression all us well established sparks will have received a shock because we got lets say relaxed and complacent with testing protocol :O/

 

[Swicade]

Personaly i'd be more than alittle concerned i'd left the house switched on (presumeing that is the situation at present) knowing there had been alot of live pipework etc before and i hadn;t found the cure for the fault yet.

Being the last Electrician on site if it happens again and someone does fall foul of the fault i'd be the scapegoat if you get my drift.

 

[Moses]

Yesterday I was installing some downlighters in a bathroom, I isolated the supply tested L-N and it was dead, grabbed hold of the choc block which was used for the existing light, stuck my screwdriver in and got an electric shock. That was weird so tested again and it was still dead so I thought it must be some lighting control gear holding a charge, so carried on and got another electric shock so got my voltmeter and measured 240v L-E and N-E. I tested various circuits and the earth was live on all of them (as you would expect), all pipework was live and even the shower cubicle was live.

The house is in the country with TT earthing and recently installed PV system which I know nothing about.

I immediately suspected the PV system and switch off the AC isolator to it which removed the voltage from the earth.

A while later I went to try to find the cause of the problem and switched the isolator back on, checked the PV was generating but no voltage on the earth.

Tested the Ze which was 65 ohms which is OK.

Does anyone have any ideas as to what could have been the cause of the live earth and why nothing tripped out?

And yes in future I will test L-E and N-E as well.

If the pipework is copper, and no PVC is installed, and all bonding is installed

Then if the pipework was live, the only explanation can be that,

the live bus bar is shorted to the earth bar, through some wire or other.

 

[vernam616]

Possible borrowed neutral

backfeeding from another circuit, when you test between earth you will get 240v, same with the pipework, with recent PV works id expect the install to meet 17th, so gas/water bonded to earth, hence why you will get 240v between(borrowed) neutral and pipework

i cant see it being connected directly from the busbar

Should be easy enough to identify

 

[Moses]

Possible borrowed neutral

backfeeding from another circuit, when you test between earth you will get 240v, same with the pipework, with recent PV works id expect the install to meet 17th, so gas/water bonded to earth, hence why you will get 240v between(borrowed) neutral and pipework

i cant see it being connected directly from the busbar

Should be easy enough to identify

If its a borrowed N, RCBOs should trip, none have?

If its a earth fault, and if all RCBOs are functioning properly, and none have tripped

Then the fault is before the RCBOs

i.e. at the busbar.

 

[vernam616]

Should have read the full thread, i never noticed the post about RCBO's


Surely the main fuse is going to go if the busbar is linked to earth

I dont think we are getting the full story and i dont beleve the OP has scoped out the job fully, simply from the lack of testing for dead

 

[Richard]

What tests have you performed apart from what was stated? You said that you tested Ra and got 60 odd ohms, but was this present at the fittings (Zs)? It's really very difficult to say as there are so many variables.

Out of interst, in what state have you left the installation knowing that theres a serious fault?

 

[Philpot]

I agree with Moses that you must check out the RCBO and exactly where the PV connects to the whole system. I have had little experience of PV's but it looks as though the PV is feeding back onto the bussbar. If you hadn't said otherwise I would have thought that the TT earth was not connected and the earth was floating. Do the RCBO's have their functional earth's connected?
Let us know exactly what you do find. Only sorry I can't be more help.
Philpot

 

[AndyL]

Reading the OP I see this is a TT system, so should surely have main RCD, not sure why this is not tripping. Think you need to do full test, cant see how all pipework can be live if you have earth connected and RCD and RCBOs