RCD trip help

[sirocco]

Just been called out investigate RCD tripping on downstairs ring at my parents it just went in the early hours with no history. Have unplugged all appliances from the 10 sockets on this ring and switched all sockets off. There are no other appliances fed from this ring other than those plugged in via sockets. There are 3 other circuits protected by the same RCD in the CU ie Shower, Cooker and upstairs ring, these are all functioning normally and don't trip the RCD. I have substituted the downstairs ring MCB but the circuit still trips the RCD immediately when the MCB is switched on with nothing plugged into the sockets. My next step is to disconnect the ring, split the dead ring at the midpoint and test each half, but before doing this I removed the 2 CPCs for the ring at the CU from the earth bar and the circuit now stays on and doesn't trip. Before I plough on , disconnect the phase and neutrals and do dead circuit testing is there anyway that I can identify why the disconnection of the CPCs allows the ring to operate? Graham

 

[sirocco]

Well I split the ring between living space and kitchen, and before disturbing the CU wiring too much decided to identify which phase supplied which ring, so far so good. Then traced round each half of the ring to check resistance between the socket where I split the ring and the others on the each half. joined phase and neutral at the split and measured across phase and neutral at each socket. Obtained nice set of readings between 0.37 and .49 for each socket except 1 which was 0.8 checked the connections in the back this one and found neutral needed tightening, this socket then read 0.38. I then livened up the living space radial , no trip. Disconnected and livened up kitchen radial ,no trip! Reconnected the ring where I had split it and livened up the whole ring, No Trip! Performed Z1 using Fluke and reading was 0.51 ohm and 431 amps. So have not carried out the Ir yet and am awaiting the next trip , if it happens.

 

[monkeyelectric]

Well I split the ring between living space and kitchen, and before disturbing the CU wiring too much decided to identify which phase supplied which ring, so far so good. Then traced round each half of the ring to check resistance between the socket where I split the ring and the others on the each half. joined phase and neutral at the split and measured across phase and neutral at each socket. Obtained nice set of readings between 0.37 and .49 for each socket except 1 which was 0.8 checked the connections in the back this one and found neutral needed tightening, this socket then read 0.38. I then livened up the living space radial , no trip. Disconnected and livened up kitchen radial ,no trip! Reconnected the ring where I had split it and livened up the whole ring, No Trip! Performed Z1 using Fluke and reading was 0.51 ohm and 431 amps. So have not carried out the Ir yet and am awaiting the next trip , if it happens.

Jesus christ!!

 

[tony mc]

Well I split the ring between living space and kitchen, and before disturbing the CU wiring too much decided to identify which phase supplied which ring, so far so good. Then traced round each half of the ring to check resistance between the socket where I split the ring and the others on the each half. joined phase and neutral at the split and measured across phase and neutral at each socket. Obtained nice set of readings between 0.37 and .49 for each socket except 1 which was 0.8 checked the connections in the back this one and found neutral needed tightening, this socket then read 0.38. I then livened up the living space radial , no trip. Disconnected and livened up kitchen radial ,no trip! Reconnected the ring where I had split it and livened up the whole ring, No Trip! Performed Z1 using Fluke and reading was 0.51 ohm and 431 amps. So have not carried out the Ir yet and am awaiting the next trip , if it happens.

I think you are missing the point the RCD tripping is telling you that there is a Line CPC fault ,whats the point in doing the above.

You now have your test equipment out so use it and do the job correctly !


Whats a Z1 test ?

 

[guest119]

It looks like we have been trying to help a Electrical Trainee?
Original post looked like he knew what he was talking about/doing but it all went downhill from there.
Im glad Im not his gaffer and paying him to carry out the wrong tests.
How many times was IR and L-E mentioned as advice?
On the up side, a potentially slack N-N fixed.

Boydy

 

[guest119]

Whats a Z1 test ?


Something from Top Gear?

 

[sirocco]

Thanks for all the encouraging and supportive remarks!! The point of my post was that I wanted to fully trace the circuit to identify what was on the ring and that there were no bridges etc. and in the course of doing this the tripping fault is no more.If it repeats I will move on to full Ir testing. But if if was that slack neutral then there will be no repeat. Interesting of course that people have been insisting that it must be a LE fault!

 

[tony mc]

If it was a slack neutral it would of still tripped with the MCB off as the RCD coil would still see a imbalance.

IMO you need to fully test the circuit or you may be getting further calls re tripping if your original information was correst.

Good luck !

 

[GLENNSPARK]

Thanks for all the encouraging and supportive remarks!! The point of my post was that I wanted to fully trace the circuit to identify what was on the ring and that there were no bridges etc. and in the course of doing this the tripping fault is no more.If it repeats I will move on to full Ir testing. But if if was that slack neutral then there will be no repeat. Interesting of course that people have been insisting that it must be a LE fault!

right then...RCDs letting go:

1)identify any plugged in/connected loads and isolate...then check if the problem persists..

2) if problem persists ramp the device off load .....anything below 15mA should be replaced...

3) if the RCD is good but problem persists then check all terminations on the RCD in the board...then move on to continuity of final....

4)if the problem persists then IR between phase-earth and neutral-earth.....you dont need to IR between live conductors (very important when time is of the issue)

 

[telectrix]

If it was a slack neutral it would of still tripped with the MCB off as the RCD coil would still see a imbalance.

IMO you need to fully test the circuit or you may be getting further calls re tripping if your original information was correst.

Good luck !

disagree. if MCB is off there is no current flow in L. there will also be no current flow in N, slack or not, unless there is a leakage N-E.

 

[tony mc]

Thats what I was getting at Tel as the signs are a N/E leakage when the breakers off!

edit L/E fault

It is sunday

 

[spark 68]

disagree. if MCB is off there is no current flow in L. there will also be no current flow in N, slack or not, unless there is a leakage N-E.

How can that be the case here Tel ?

The OP said it was tripping as soon as the MCB was on with no loads connected, he also (dangerously) disconnected the CPC re-energised and it stopped tripping.

All of this points to a L-E fault.

Something is not adding up here.

Ps. agreed a slack Neutral can cause tripping, but not the way the Op described this situation.

 

[guest119]

0.8 is hardly slack!

 

[monkeyelectric]

0.8 is hardly slack!

I just done an eicr and the rn value is 900 ohms whilst the r1 is 0.9, now thats slack!

 

[SimpleSimon]

Coming back 24 hours later and nothing is tripping out on the RCD? Possible dampness in the back of a box that's dried out?

 

[sirocco]

Not so Simple Simon has probably hit the nail on the head. The original scenario I described was accurate and everything points to a LE fault. I just did a bit of tracing in an unconventional style and tidied up a slackish neutral in a socket on the ring. 24hr hours later all has been reconnected, circuit does not trip with or without loading, Loop impedance shows 0.51 ohms 431 amps. So what could have caused original LE fault.? Water/condensation in kitchen area which has now dried out- quite likely. A rodent chewing and bridging LE before keeling over - less likely Conductors overheating and expanding to bridge LE via a nail or other foreign object- most unlikely as fault occurred with no load and Loop Impedance reading shows circuit has plenty of surplus capacity. I vote for water which has now dried out and will look for that problem if any reoccurrence. Thanks again for everyones help and interest. Graham