RCD Problems

[N1G3L]

We installed a new split load consumer unit in a large country house about 2 years ago. No Leakage protection existed before and there were a few faults that had to be sorted. A Neutral/Earth short in one socket and very rat chewed cables replaced. The system worked fine until recently. The RCD trips for no apparent reason. Another (MK) unit was substituted but the fault remains. Trouble is no particular circuit seems responsible for the tripping. All MCBs have to be turned off before the RCD will reset. Whilst turning on the circuits one by one even in different order any one with an apreciable load attached will cause RCD to trip.
This fault is very strange and has got me completely stumped. I do not have a megger tester but do have a very good quality DVM.

1. What is the correct way to test all these circuits?

2. Should Neutral be tied to Earth inside supply termination box, ie. before the main company fuse?

 

[equipotential]

I've got a strange problem: replaced an old fuse box with a Consumer Unit before Christmas. Now a couple of lights (non-RCD) trip the RCD when switched off!? I've checked for cross neutrals, meggered all the cables. The only oddity I can find is that some of the cables appear to have a floating ac voltage (around 20V) even if disconnected at both ends? Weird! Any ideas/suggestions?!

hi grsebs

could you just clarify for me

am i correct in understanding that the lighting circuit in question is NOT protected by the 30ma rcd?
and that the db is a split load consumer unit?

is the circuit in reference a 2way lighting circuit?

if it is then how is it wired

a 3-core and earth between switches with a twin (live /switch wire) to the light from one of the switches

or is it wired in singles with a live feed at one switch and a switch wire at the other switch?

are there any intermediate switches between the 2-way system?

are the light fittings class 1 or class 2? and how many


equi

apologies folks posted on wrong thread please ignore

 

[RF Lighting]

1. What is the correct way to test all these circuits?

With an insulation resistance tester.
A "very good quality DVM" can not output 500V DC, so is not good enough.

2. Should Neutral be tied to Earth inside supply termination box, ie. before the main company fuse?

Depends on the supply type. It is certainly not something you should be interfering with though.

 

[ericmark]

1. What is the correct way to test all these circuits?
There are books to tell you this but next question gives a clue without doing this.
The idea of the C&G 2391 course and exam is to show electricians how to inspect and test this takes typically 30 hours spread over 12 weeks and has a high failure rate even when electricians take the course and to explain in a forum is not really going to happen.
2. Should Neutral be tied to Earth inside supply termination box, ie. before the main company fuse?
No with main incoming isolator off there is no connection between earth and neutral. Some sockets with voltage spike protection may give a small leakage around 0.3ma and where fitted a 250 volt rather than 500 volt test is done. But 230/0.0003 may give 750Kohm in theory but because the insulation tester is DC and the 0.3ma refers to AC leakage it does not work that way.

Eric