Hello people 1st post. I am a apprentice and I would like to clear up something. RCDs do they need cpc to operate ? As if there is no earth faulth path for the imbalance to flow down then an imbalance cant be detected ? The reason I ask this is because I went to a job with the person I worked with and there was a fault on a lighting circuit, established what circuit it was. Now when he energised that circuit after about ten seconds the rcd would trip. There was about 12 fittings on that circuit all cat II. What he done was disconnect the cpc at the board and then energise the circuit, and then the rcd did not trip, whilst it was like this he found the fitting which had a ballist inside sizzling. my question is why did the rcd not trip if it runs on an imbalance fault between line and neutral, because the cpc was disconnected. Are Rcds pointless without a good earth path for the current to flow down so the imbalance is detected. All your thoughts and views will be appreciated. Thank u in advance.
RCD
- Thread starter young5
- Start date
Sponsored Links
RCDs do not require an earth connection to work. If current flows anywhere other than via the line and neutral, the RCD will trip.
This could be via the CPC, or just as easily via a damp wall or through a person.
Operating a circuit with the CPC disconnected is dangerous and completely unnecessary. In this instance it is likely that the CPC and anything connected to it could have been live, just waiting to kill whoever came into contact with it.
This could be via the CPC, or just as easily via a damp wall or through a person.
In that case the fault was between line and the CPC or neutral and the CPC.
Operating a circuit with the CPC disconnected is dangerous and completely unnecessary. In this instance it is likely that the CPC and anything connected to it could have been live, just waiting to kill whoever came into contact with it.
Thank u flameport for clearing that up for me. So because of the fault between line and earth or neutral and earth the rcd is picking this up and then is tripping out because of the imbalance. This has cleard things up for me alot. However with the cpc disconnected and if anybody had come in contact with the circuit the rcd should trip under 200ms or 300 ms so it is giving the addional protection??
T
tonyelectric
Hi Young 5, welcome and firstly congratulations on choosing a most rewarding and interesting career.
An RCD has a torroidal transformer inside with three windings, think of a ring of iron with the live wrapping around one side the neutral the other and a third coil with many more turns at the top.
If current flows conventionally in the circuit then the two side coils cancel each other out and nothing occours in the top coil, now suppose there is a break down to earth somewhere in the circuit, this causes an inbalance between the two coils resulting in an induced current in the third, this current then trips the device.
Another way to think of this effect is like a steering wheel, with both hands exerting equal pressure either side (L & N) nothing happens, but if either exerts more pressure the car moves, or in an RCD the trip operates.
In the beginning RCDs were often made out of an MCB and a separate transformer assembly, you are bound to find one of these eventually.
So as flameport says the earth wire is not a requirement, just a passage to earth - also second the motion that operating a circuit with no earth is madness.
An RCD has a torroidal transformer inside with three windings, think of a ring of iron with the live wrapping around one side the neutral the other and a third coil with many more turns at the top.
If current flows conventionally in the circuit then the two side coils cancel each other out and nothing occours in the top coil, now suppose there is a break down to earth somewhere in the circuit, this causes an inbalance between the two coils resulting in an induced current in the third, this current then trips the device.
Another way to think of this effect is like a steering wheel, with both hands exerting equal pressure either side (L & N) nothing happens, but if either exerts more pressure the car moves, or in an RCD the trip operates.
In the beginning RCDs were often made out of an MCB and a separate transformer assembly, you are bound to find one of these eventually.
So as flameport says the earth wire is not a requirement, just a passage to earth - also second the motion that operating a circuit with no earth is madness.
Sponsored Links
T
tonyelectric
So as flameport says the earth wire is not a requirement, just a passage to earth - also second the motion that operating a circuit with no earth is madness.[/quote]
Just to clarify that the earth wire is not a requirement for the RCD to operate, it is of course a technical and safety requirement
Just to clarify that the earth wire is not a requirement for the RCD to operate, it is of course a technical and safety requirement
H
holmslaw
..
H
holmslaw
..
Check applied load is compliant with OPD, condition of load /appiance/ or current using device , and any switching device in cicuit Continuity, IR, of ALL concuctors I know a lot of guys link L & N for the IR test if there is a connected load/neon etc but I always remove loads even if it means de-lamping an entire circuit.
DM
PS marks out of 10 ?
DM
PS marks out of 10 ?
H
holmslaw
..
Hmm I wonder any hoo matters not a jot,
I would advise young5 to get a copy of guidance note 3, inspection & Testing published by the IEE and wilst it is not a troubleshooting or fault finding guide it will if followed be just as good if not better, and once these tests and procedures are learned they will become your standard points of reference for most fault tracing
DM
I would advise young5 to get a copy of guidance note 3, inspection & Testing published by the IEE and wilst it is not a troubleshooting or fault finding guide it will if followed be just as good if not better, and once these tests and procedures are learned they will become your standard points of reference for most fault tracing
DM
Spark123 they are as holmslaw has described them.
Holmslaw - As this was actually a line - earth or neutral - earth fault the rcd was detecting the inbalance. is it correct to think this ?
Maguire - For an insulation resistance test if done on this circuit at 250v with everything connected would that be ok, as in it will not damage the ballasts? I know on a circuit if 230 v then it should be 500v and the minimum acceptance value is 1Mohm and anything under 2 should be investigated further. Just to see what value you would get at 250v?
Also I would like to ask you if you did carry out this test at 500v with the fittings connected, and the line and neutral connected together and tested to earth would you damage the ballasts and the other equipment inside the fitting?
Also as the fault lied with the ballast, How would you have determined this fault? As the cables supplying the fittings would have been in good working order ? insulation resistance value would have been fine ?
Thank u all in advance, and Maguire thank u for recommending Gn3, I will be getting that asap.
Holmslaw - As this was actually a line - earth or neutral - earth fault the rcd was detecting the inbalance. is it correct to think this ?
Maguire - For an insulation resistance test if done on this circuit at 250v with everything connected would that be ok, as in it will not damage the ballasts? I know on a circuit if 230 v then it should be 500v and the minimum acceptance value is 1Mohm and anything under 2 should be investigated further. Just to see what value you would get at 250v?
Also I would like to ask you if you did carry out this test at 500v with the fittings connected, and the line and neutral connected together and tested to earth would you damage the ballasts and the other equipment inside the fitting?
Also as the fault lied with the ballast, How would you have determined this fault? As the cables supplying the fittings would have been in good working order ? insulation resistance value would have been fine ?
Thank u all in advance, and Maguire thank u for recommending Gn3, I will be getting that asap.
Thank u tonyelectric for the detailed explanation and the warm welcome
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
