rcd trip on ring main

[meady]

I carried out a cu change today and came across a problem I couldent solve

The sockets are all on 1 ring main throughout the house 2.5mm t&e on a 32a mcb. its a tncs, Ze 0.21 pfc 709

I carried out the dead tests which came out as R1=0.21 Rn=0.22 and R2=0.71Insulation was >500 on live live and >500 on live earth (happy days)

I went live and attempted the zs test, as soon as I pressed the test button the rcd triped. I reset the rcd and tried again with the same out come. I once again reset the rcd and pluged the kettle in the socket. after about 2 seconds it tripped. It seemed to trip every time a load was put onto the circuit. Out of curiosity I wired the ring on the non rcd side and tested the zs. I got a reading of 0.71. Im confused by now.

The last resort was changing the rcd but it had the same outcome. Can anyone suggest the best methods of tracking down the problem as Im very confused on this one, all tests seem fine and it only trips when there is a load added to it.

 

[a1]

Is it a split load? Neutral connected on wrong side?

 

[Andy™]

your R2 is very high - should be about 0.36.

how many other circuits are on the RCD?

 

[meady]

Is it a split load? Neutral connected on wrong side?

its a wylex 10 way dual rcd board but only 5 circuits in it at the moment. I installed the ring and up lights on one rcd and 3 circuits on the other. I thought about neutral connected wrong side but the ring is the only 2.5 mm cable in it and the r1, rn and r2 were really good, both neutrals in same bar. im stumpted big time:C

 

[a1]

[quote name='Andy

 

[meady]

[quote name='Andy

 

[Andy™]

what was IR on other circuit? if that has low IR, then current will flow from socket circuit, through other and cause RCD to trip

 

[meady]

[quote name='Andy

 

[Andy™]

400 ohms for IR? no wonder RCD is tripping. 400 ohm at 230v is 570mA

 

[PC Electrics]

It won't be 400ohm surely? Most meters won't read that low on IR (it would be 0.0004 on the Mohm scale). I think he just left out the 'M' and it's 400Mohm.

When you say "Live to earth" do you mean "line to earth" or "L & N to earth"?

 

[meady]

It won't be 400ohm surely? Most meters won't read that low on IR (it would be 0.0004 on the Mohm scale). I think he just left out the 'M' and it's 400Mohm.When you say "Live to earth" do you mean "line to earth" or "L & N to earth"?

Lol, yeah sorry dudes I left out the m, my heads not with it tonight (think it something to do with the half bottle of wine that been consumed) . I test between line and neutral, line and earth

 

[Andy™]

Lol, yeah sorry dudes I left out the m, my heads not with it tonight (think it something to do with the half bottle of wine that been consumed) . I test between line and neutral, line and earth

what happened to N-E? this is just as important. N-E fault will cause an RCD to trip

 

[batty]

Could be a faulty RCD not a Wylex by any chance, why not disconnect all the other circuits that way it will illiminate crossed neutral.

 

[meady]

Could be a faulty RCD not a Wylex by any chance, why not disconnect all the other circuits that way it will illiminate crossed neutral.

Yep it's a wylex alright. When I'm round next I'll disconnect all other circuits and just leave the ring in place then hopefully I know exactly where to start looking. Thanks for the useful advice.

 

[batty]

Yep it's a wylex alright. When I'm round next I'll disconnect all other circuits and just leave the ring in place then hopefully I know exactly where to start looking. Thanks for the useful advice.

I would change RCD first.

 

[Andy™]

i would check N-E IR first...

 

[meady]

I would change RCD first.

I did try another one but it was a used wylex i found in the van. I'll probably swap the circuit from the rcd to the other and see if it has the same outcome.

 

[meady]

[quote name='Andy

 

[batty]

Will do

Could deffinately be n-e fault missed that bit.

 

[PC Electrics]

Will do

N - E faults are a very common problem on CU changes, mainly because they do not cause a fuse to 'blow' so go undetected for years until you come along and add an RCD. So always test IR N-E.