Insulation testing earth fault... strange one

[Bez]

The strange one is that its showing 240v between L and N but check L - E and get nothing.

Correct me if i'm wrong, but the readings you are getting would suggest that the phase conductor is at zero potential, given that the L-N potential differance is 240v this would seem unlikely.

Unless of course you have reverse polarity on the DNO side, which would account for zero potential between L-E.

Ok so the problems solved:coat

 

[steptoe]

Correct me if i'm wrong, but the readings you are getting would suggest that the phase conductor is at zero potential, given that the L-N potential differance is 240v this would seem unlikely. Unless of course you have reverse polarity on the DNO side, which would account for zero potential between L-E.

well spotted,

although much more common on TT, where in all honesty it is not so much an issue as safety is concerned.

though still potentially lethal.

 

[Andy™]

although much more common on TT, where in all honesty it is not so much an issue as safety is concerned.

though still potentially lethal.

how can something not be much of a safety issue, but still deadly

 

[rstephen34]

hi

i would agree with lurch you have two circuits screwed or nailed say lights to sockets via earth to phase,screws or nails can pass through the centre t+e and not touch the phase conductors or damage the cpc and short to another cables phase,you will have to find the other circuit that is causing the problem with the sockets and test from there.

 

[steptoe]

[quote name='Andy

 

[Andy™]

because reverse polarity on PME can mean everything that is earthed may go to phase potential even though no other fault is present.and as you have NO overcurrent protection on the neutral (SP RCBOs) then ..........

TT must be protected by DP devices.

i know what you mean on the PME part - but remember that many TT systems only have SP MCB's, so if one does trip, then the circuit is still live. exactly the same as cross polarity in TN systems

 

[steptoe]

[quote name='Andy

 

[steptoe]

ok, sorry, I missed MCB for RCBO,

you still must have a DP RCD in a TT install

 

[steptoe]

ok, sorry, I missed MCB for RCBO,

you still must have a DP RCD in a TT install

 

[Apache]

ok, sorry, I missed MCB for RCBO,you still must have a DP RCD in a TT install

You said that an hour ago..............

 

[steptoe]

your PC must be slower than mine patch.!

 

[ianmacd]

Yea Patch, it was only 50 Mins .

 

[Andy™]

ok, sorry, I missed MCB for RCBO,you still must have a DP RCD in a TT install

yes, the RCD must be DP (which is why RCBO's generally are not used with them being SP)

but the fact still remins that with cross polarity, even if isolated by MCB, the circuit is still live (in the exactly same way as TN).

 

[batty]

You only need dp isolation on certain tt installs caravan parks jetties etc. As long as your main switch is dp you can use sp Rcbo's on tt.

 

[steptoe]

You only need dp isolation on certain tt installs caravan parks jetties etc. As long as your main switch is dp you can use sp Rcbo's on tt.

really........

new one on me, honestly didnt know that.

I understood that TT had to have all live conductors protected.

I stand corrected.

Im going to stop answering questions on stuff like this.

 

[steptoe]

[quote name='Andy

 

[Andy™]

which a DP RCD, (or even a DP rcbo) would pick up on and disconnect.

after youve had a shock. it shouldnt get to that stage.

preventing a shock in the first place is better than something to disconnect once your part of the circuit

 

[steptoe]

[quote name='Andy

 

[Lurch]

so you get a shock because you havent earthed properly in the first place.

Not really. I could whip a socket off and stick my finger on the live terminal, nothing to do with the lack of an earth.

 

[a1]

we really need to get reading up on the purposes of proper earthing on this forum.

You Volunteering then Steps?

:|