best procedure for finding fault

[panny300]

mate has a small unit and main rcd (not the mcb) trips when lights switched on.only two light and ring fuses in consumer
there are four fluorescents (2 are no longer used but were still connected) and two spots on the circuit(a second light circuit is ok).i have disconnected all the lights from the circuit,the rcd still trips when switched on.
at the consumer with the live/neutr/earth disconnected and using a meter there is no short between live and neutral of the circuit, but when i tried between live/neutral and earth i got a warning beep, it seems there is 14v on the earth and also the earths still connected in the consumer. (there are other fluorescents on the other light circuit could this be the reason for the 14v?)
the circuit is all singles run in metal tubing. so can anybody advise on the best procedure to test. or just rewire it?

 

[Spark123]

Has any work been done recently? What are your Insulation Resistance reasings for L-E on the lighting circuits? Are there any outside lights/cables/junction boxes?

 

[panny300]

only the four fluorescents and two spots on the circuit,
did,nt do ins resistance due to the 14v on the earth,and could'nt turn off supply to the consumer to as the other circuits were in use,having another go tomorrow night.so what would be the best way to proceed

 

[pdcelec]

only the four fluorescents and two spots on the circuit,
did,nt do a loop impedance due to the 14v on the earth,and could'nt turn off supply to the consumer to as the other circuits were in use,having another go tomorrow night.

Note the highlighted word. No such problem unless there is a life support machine connected to it

 

[RF Lighting]

only the four fluorescents and two spots on the circuit,
did,nt do a loop impedance due to the 14v on the earth,and could'nt turn off supply to the consumer to as the other circuits were in use,having another go tomorrow night.

Note the highlighted word. No such problem unless there is a life support machine connected to it

That would really upset the IT geeks in one of the offices we work in.
They treat their beloved server cabinet as a life support machine

 

[panny300]

i switched the mcb to the circuit off before disconnecting, and was confident with what i was doing. i can even cross roads without waiting for a beeping sound telling me it,s safe to cross.god i hope the regulation police are'nt reading this.
anyway can anyone tell me the best way to proceed.thanks

 

[pdcelec]

use the correct test equipment and follow the correct test procedures and you will find the fault. There are no short cuts, no alternatives to correct test equipment and no substitute for experience. Either you to find the problem or you dont, it is up to you

 

[panny300]

i have test equipment,have you read my previous posts?,i have been asking for the correct procedure.thanks

 

[Spark123]

Turn off the supply and do a L-E and N-E IR test (disconnect any vulnerable equipment 1st). This should tell you if you are looking for an earth fault. Its basically a case of starting at one end and working your way through. If it is an earth fault and you can disconnect at a point mid way through the circuit, see which way the fault is from and narrow it down from that. This is called the half-split method.
Things on the list that can cause RCDs to nuisance operate include; borrowed neutrals, miswired fittings, water ingress, mechanical damage, wrong neutral bar in a split load cu.

 

[panny300]

thanks spark ,thats the sort or info i was hoping for