RCD tripping

[markadams]

Hi,

Got called to a jobs due to the RCD tripping on the downstairs ring, as soon as the MCB for the ring is turned on the RCD trips.

I didn't have long but I did some quick tests, R1+R2 was fine on all sockets so I split the ring about half way and did an IR test on each side of the ring and got 0.01 ohm on both sides.

I had to go to another job but I am back tomorrow.

Any suggestions for what may cause this? or testing

 

[telectrix]

swap you my fault for yours. :28:. 2 of us been on it 5 hours so far. found one - still another under the main bedroom floor,

seriously. you need to diss both the Ls and the Ns from CU before testing. if it's PME then diss the cpc's also. if your dissed circuit is then clear, it could be a fault on another circuit.

 

[markadams]

I did disconnected the L,N and cpc so this was not the problem.

Mark

 

[bigspark17]

Why are you doing an r1-r2 test when called out to an instantaneous rcd fault which is already isolated to that mcb by customer.? And why have you left there if you haven't found it.?

 

[HandySparks]

...so I split the ring about half way and did an IR test on each side of the ring and got 0.01 ohm on both sides.

Between which two conductors?

if it's PME then diss the cpc's also.

Why so?

 

[assegayer]

Why would you go there and just do r1 and r2 tests and leave, just apply some common sense,

1.) split the ring, does it still trip?
2.) split again so there is only one socket on the mcb connected, does it still trip?
3.) keep splitting till it doesnt trip then you have found the area of cable where theres an issue.

 

[bigspark17]

Im assuming all appliances have been disconnected/isolated,?

 

[telectrix]

and look for any pretty pictures or shelves fixed above sockets.

 

[Octopus]

So the ring has been split and you have identical IR readings on both halves - this sounds very odd to start with

 

[markadams]

assegayer, did you read my post? I didn't just do an r1+r2 test then leave, I split the ring and did an IR test on each side. The customer called 4 other electricians and no one else turned up, I was very busy and needed to get to another job but said I would pop in and have a quick look and come back when I had a bit more time tomorrow.

I did an r1+r2 on one side of the rings so I could work out the middle of the ring so I could split it.

 

[markadams]

Murdoch,

I agree that it sounds very odd which is why I wanted to get some views on here, I have done a fair bit of fault finding but never had this scenario.

 

[assegayer]

assegayer, did you read my post? I didn't just do an r1+r2 test then leave, I split the ring and did an IR test on each side. The customer called 4 other electricians and no one else turned up, I was very busy and needed to get to another job but said I would pop in and have a quick look and come back when I had a bit more time tomorrow.

I did an r1+r2 on one side of the rings so I could work out the middle of the ring so I could split it.

Yeah I read it all im suggesting is that you remove all appliances then see if it still trips....then disconnected all other sockets expect for the first one on the ring see if it trips. then keep doing that I.e. 2 sockets then check then 3 sockets then check

 

[markadams]

I would add that I am told that the house was majorly flooded and has been empty for 10 years until recently when I different spark installed a new CU (the customer called him and he never replied to the calls/messages). The power has been working for the last 2 months then suddenly stopped.

All other circuits are working fine.

 

[assegayer]

Have you asked the customer if any shelves or any sort of drilling or hammering into walls has happened. if not then just do the procedure i an other mentioned will definetly find your fault..

 

[SJD]

assegayer, did you read my post? I didn't just do an r1+r2 test then leave, I split the ring and did an IR test on each side. The customer called 4 other electricians and no one else turned up, I was very busy and needed to get to another job but said I would pop in and have a quick look and come back when I had a bit more time tomorrow.

I did an r1+r2 on one side of the rings so I could work out the middle of the ring so I could split it.

While not impossible, I'd say it was a bit unlikely you have 2 faults both measuring 0.01 M Ohm (I assume that is what you meant to say). Are you sure the two sections of the ring are isolated from each other - L, N and E - and you don't have some interconnection somewhere, e.g. it is wired as a figure of 8?

EDIT: just seen your post about all being damp for 10 years, perhaps there is leakage in lots of places, which adds up to about the 10 kOhm you are seeing, given that an MFT is not that accurate right at the bottom of the scale - one reading could be 6 kOhm (all the RFC) and one 14 kOhm (each half of the RFC), both rounded to 10 kOhm when displayed on the MFT. For example, damp dirt in socket boxes or junction boxes.

 

[Octopus]

Murdoch,

I agree that it sounds very odd which is why I wanted to get some views on here, I have done a fair bit of fault finding but never had this scenario.

When you had split the ring, with both halves disconnected at the cu, did you check for continuity between them as it sounds like there is an interconnection

 

[markadams]

Everything is unplugged.

Assegayer, that was my next thought also, I just cant understand how it has a fault on both sides

 

[markadams]

Not yet Murdoch, will try tomorrow.

 

[Octopus]

Not yet Murdoch, will try tomorrow.

has to be your next test, but after rechecking the IR between the 3 cores

 

[happysteve]

Either two faults, or, there is another interconnection in the ring (ie wired up like an "8", not a "0").

Edit: oops, too slow!