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

 

[monkeyelectric]

Ir test

 

[babylonsBurning]

It indicates that you have a live to earth fault. Insulation resistance test would show this. Then split the ring half way, test again and continue this procedure.

 

[ALD]

Double check that there isnt a faulty imersion wired on the ring. Ive had this before.

 

[guest119]

Looks like an all insulated ring with no parallel paths and earth from the cpcs only.
Then leakage through maybe dampness. Underfloor joint box, painters been using a steam stripper and water running into the sockets, dampness by other route to sockets on external wall etc etc.
As already stated, IR wins.

Boydy

 

[GLENNSPARK]

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

so Graham....after removing the 2 CPCs then energising the circuit (a no no for a start)...did you expect the device to still let go?

 

[Jabbajaws]

This could be something as small a hole in a conductor sheath, with the bare wire touching a metallic backbox. Ive had this happen before. Check for recently hung pictures and nails which may have been inserted, into a wall perhaps, somewhere on the cable run.

If you have an RCD activating and there is no load, there has to be an earth fault in a place where you would least expect to find it...

And like GLENNSPARK says. If you disconnect the CPCs on the ring. The RCD that protects it, will not operate as it wont detect the earth fault...

 

[sirocco]

The RCD is protecting the other three circuits and is operating under load. I was trying to understand why Babylons Burning suggests that it points to EL fault rather than say EN fault. At 8am tomorrow I will be back on the case with my trusty Fluke, split the ring and crack on. I have a feeling it will turn out to be in the kitchen, where steam abounds! There is also some evidence of mice in the kitchen and I wonder if they have been chewing on a wire. As always any other helpful suggestions welcome.

 

[Cnobby]

It could be either a LE fault or NE fault. I would definitely do an IR test and then identify which cable is giving you the problem. If it is a cable and difficult to replace, i would split the ring and have two radials if you have the room in the CU.

 

[spark 68]

It could be either a LE fault or NE fault. I would definitely do an IR test and then identify which cable is giving you the problem. If it is a cable and difficult to replace, i would split the ring and have two radials if you have the room in the CU.

It will be a L-E fault, as the RCD trips only when the MCB (single pole) is on.

Glenn is correct, the CPC's should never be removed to fault find live, as this is a hazard.

 

[Sintra]

If it was a N-E fault the RCD would not hold at all. What the OP has described would appear to be a L-E problem.

 

[Ducksy]

Awwwww man this would be a perfect opportunity to use my new earth leakage clamp meter........some people get all the fun

 

[GLENNSPARK]

Awwwww man this would be a perfect opportunity to use my new earth leakage clamp meter........some people get all the fun

there`l be plenty of time for that....
knowing some of the DIY crap & dodgy appliances going about now...

 

[tony mc]

Awwwww man this would be a perfect opportunity to use my new earth leakage clamp meter........some people get all the fun

I can't see a clamp meter being any good if the RCD will not hold !

Disconnect the circuit split the ring if it is a ring and start your IR testing.

 

[telectrix]

could bypass the RCD, strictly for clamping the leakage, of course.

 

[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

 

[GLENNSPARK]

Whats a Z1 test ?


Something from Top Gear?

yes....its called `see how fast you can get round the circuit`....

 

[electric will]

Whats a Z1 test ?


Something from Top Gear?

maybe something to do with the new BMW.

 

[power ranger]

If the OP is using a fluke mft and doing dead tests then he would be setting his tester to "Rlo" for a low ohm continuity test and not Z1 as this is for loop tests.

Im thinking that it could have been a "pinched" Line conductor on one of his steel k/o boxes, and he has just been lucky that when screwing the socket outlets back after testing the orientation of the conductor has been altered and now not causing a L-E fault.

Just as a note to the OP. If you do go back and carry out IR tests, then leave the CPCs in the earth bar when testing!

 

[GLENNSPARK]

If the OP is using a fluke mft and doing dead tests then he would be setting his tester to "Rlo" for a low ohm continuity test and not Z1 as this is for loop tests.

Im thinking that it could have been a "pinched" Line conductor on one of his steel k/o boxes, and he has just been lucky that when screwing the socket outlets back after testing the orientation of the conductor has been altered and now not causing a L-E fault.

Just as a note to the OP. If you do go back and carry out IR tests, then leave the CPCs in the earth bar when testing!

aye and if it goes to fault while he `tests` this circuit with CPCs disconnected he could end up pinching one off n all (involunatry)

 

[Deleted member 9648]

Cant believe some of the ceerap posted on here....the OP has a tripping RCD and he STILL hasnt IR tested???.....thats the first effin' thing to do for $%*&'s sake!

 

[sirocco]

If the OP is using a fluke mft and doing dead tests then he would be setting his tester to "Rlo" for a low ohm continuity test and not Z1 as this is for loop tests.

Im thinking that it could have been a "pinched" Line conductor on one of his steel k/o boxes, and he has just been lucky that when screwing the socket outlets back after testing the orientation of the conductor has been altered and now not causing a L-E fault.

Just as a note to the OP. If you do go back and carry out IR tests, then leave the CPCs in the earth bar when testing!

Obviously used the low resistance setting for the resistance tests and did the loop impedance at a socket using Zl no trip setting once circuit was all reconnected and live. Is leaving the CPCs in the earth bar best practice? I thought that to test the insulation resistance of a particular circuit that each element to be tested LE and NE needed the 2 conductors and CPC to be fully isolated to be sure that readings related to that length of cable only. ?

 

[power ranger]

Sorry got to be quick, but if you removed cpc,s from met, tested IR, then how would you know if there was a fault from a live conductor to any extraneous metal in that installation?
Therefore by keeping the cpc's in the met and putting your test lead on that and your other lead on the circuits L or N, then you will be verifying that all earth parallel paths are isolated from live conductors.

 

[bertt]

Hi,

The RCD-30mA if it is for a few circuits in your Consumer Unit , actually will make a vect.sum(a result) of all your possible leakings about circuits on L&N(3,4...circuits).
I don't know the history of your problem linked with particular event or not during the day,night. Please ask your parents when they observed the missing of power.. what they did then? Could be helpful.
About your (new, with RCDs) Consumer unit:
please double check inside the CU wrong tightening of wires It could make overheating and or false connections.

So,
I.
- One by one the modules MCBs and next RCDs 'OFF' about Consumer Unit.
- Then Main Switch OFF
- open the CU box
- Visual proper inspection of all modules as integrity(colour, shape) and IN/OUTs contacts and tightening. Use the electrician light torch(head one) ,screwdrivers....
- search any clues of overheating area IN, OUTs, MCBs, RCD.
if ok all above follow next steps...

- remove the circuit as wires(phase & neutral)you suspect as cause of RCD tripping. From OUT MCB circuit.

II.
- reconnect the Main Switch(ON)
-Then in order the RCD where is comming your circuit through MCB.
and after the MCB itself .Your circuit still away from OUT MCB who belongs.

A- Now, if the RCD is tripping after MCB circuit swiched 'ON' it is something inside the Consumer unit the problem not the circuit.
if not ..
B- add all the others circuits(switch 'ON')from same RCD group.If same, RCD it is not tripping the cause it is somewhere on circuit but I bet on Consumer unit connections problem.
(Don't forget after to reconnect the circuites.
Main switch 'off ' reconnect the wires proprely L,N to MCB,.
Switch ON Main switch and one by one RCDs and after MCBs. Double check and Test IN OUTs and TEST RCD .Close the Consumer Unit BOX.
Thank you.

All the best.

bertt.imp:

 

[KAS1]

can someone translate the above please lol

 

[Engineer54]

can someone translate the above please lol

You and me Both!! ..lol!!