am i on the right track with this

[tom1]

a while back did cu change and installed rod.

it about an hour away so the guy called some one local when his shower or tumble dryer are on the rcd trips. the local guy has no test equipment with him and says the rcd is too sensertive and advises replacement.

so he rings me to come out as i fitted the cu so its under warrenty.

got there and ramp tested with loads connected on a socket, >51ma

flicked to loop test and go about 0.4 ohms

the rod i put in had an ra of about 50 ohms, tested the rod, 42 ohms.

tested the rcd in isolation triped at 25ma, tested at board with neutrals connected >51ma.

so i ir the shower and ring final, E N short on the ring. he said he has had no work done to that circuit and has not been hammering nails in around the sockets. so i narrowed it down between 2 sockets and above one was 2 pics hanning on nails pulled nail out and the fault cleared. pulled new cable through and all working.

so when ramp testing with neutrels connected the current was drawn throught the meter throught the earth bar through the ring cpc N E short then back through the rcd with no imbalance so did not trip?

the low zs on the ring again the current passes through cpc to neutral, so return path is the neutral?

think that explains it?

what do you guys think thanks

 

[Larnacaman]

Trying to work out what your saying here, but any neutral earth fault on the load side of an RCD device will trip the RCD .... that is part of it's function in life.

So what was the fault on the shower unit then??

 

[tom1]

i am on about the ramp test not tripping due to the N E fault

 

[NozSpark]

Trying to work out what your saying here, but any neutral earth fault on the load side of an RCD device will trip the RCD .... that is part of it's function in life.

Not necessarily with a TT installation...

N-E faults can go undetected

 

[tom1]

it only tripped with a big load like the shower or dryer on the faulty circuit, on a different circuit same rcd the dryer worked

 

[Larnacaman]

It's late here, so maybe i'm missing something or misinterpreting what you have written. but you are saying ''N-E Short'' ....what short are you talking about??

Edit....

Ah, ....forgetting about the TT earthing...lol!!

I would have thought with a 42ohm earth it would have still tripped .... but i can see that it may well not.

 

[Apache]

Tom - I think you need an earth leakage meter as recently discussed!

 

[sellers]

a N-E fault wont trip an RCD if no load is applied on that particular circuit, If I am thinking right in my noggin.

 

[tom1]

i need lots of things mate, do you know were i can buy a winning lottery ticket, prefrebly euro millions. the ones i get are duds

 

[Apache]

i need lots of things mate, do you know were i can buy a winning lottery ticket, prefrebly euro millions. the ones i get are duds

I bought one on a whim tonight. If I'm a millionaire I'll buy you one!

 

[spinlondon]

It could be that the neutral to earth fault caused by the nail was only allowing a small fault current to leak and that when the other two were on their leakage took the total high enough for the RCD to trip. It could be that the neutral to earth leakage increased on damp or rainy days.

Who knows?

 

[Apache]

a N-E fault wont trip an RCD if no load is applied on that particular circuit, If I am thinking right in my noggin.

Cut a cable [shorting either N-E or L-E] with the MCB off and see what happens to the RCD. :Salute

 

[spinlondon]

a N-E fault wont trip an RCD if no load is applied on that particular circuit, If I am thinking right in my noggin.

It would allow the current from other circuits to leak to earth as the neutrals on all the circuits are connected.

 

[tom1]

I bought one on a whim tonight. If I'm a millionaire I'll buy you one!

fingers crossed:good luck:

 

[NozSpark]

It could be that the neutral to earth fault caused by the nail was only allowing a small fault current to leak and that when the other two were on their leakage took the total high enough for the RCD to trip. It could be that the neutral to earth leakage increased on damp or rainy days.Who knows?

Thats exactly it... remember the L-E loop could be 200ohms (on a TT) where as the L-N loop is more than likely to be <0.8ohms