RCD sensitivity

[electrics]

"Since RCDs complying with IEC and many national standards may operate under,
the limitation of permanent leakage current to 0.25 IΔn, by sub-division of circuits
will, in practice, eliminate any unwanted tripping" what does it mean? i couldnt understand it. Technical uses sometime confuses me, for example" operate" here means tripping or just "go on installation " ? what is this 0,25 ? some explanation pls...As far as I know many rcd İs manufactured as unadjustable am i right?

 

[winnie]

RCD means 'residual current detector'. It is a device that measures the net current flowing on all of the intentional conductors of a circuit.

For a correctly functioning circuit, _all_ of the current going 'out' on one conductor must be matched by the current flowing 'in' on the other conductors, thus the net current should be zero. Any measured net current means current flowing via an unintentional path, eg. a fault to ground or to another circuit.

The I delta n notation means the current level at which the device will open the connected circuit. Different RCD devices will have different ratings, eg. 0.006A for life safety or 0.250A for fire protection.

If you have multiple separate circuits fed from a common source, they could all be protected by a single RCD at the source. However this shared RCD would detect the _total_ leakage to ground of all of the circuits, which could lead to 'nuisance tripping' if the leakage on any individual circuit were low enough to be acceptably safe. Additionally such a shared RCD would not detect circuit to circuit faults. Using multiple separate RCDs on each of the individual circuits, or even breaking circuits up and protecting the portions with their own RCDs ("sub-division of circuits") localizes the sensitivity of the RCD to individual circuit locations.

-Jon

 

[electrics]

what i cant understand is 0,25 Ires. what does it mean here with this operating under phrase....

 

[ELA]

It always helps to [post the context in which you are asking from. As in here:
http://www.electrical-installation.schneider-electric.com/ei-guide/pdf_files/EIG-F-protection-electrical-shocks.pdf (page 38)

I interpret this to mean that there is normal leakage current in all circuits and so they are suggesting limiting this by sub division of circuits.
Keeping the "normal" leakage current in a circuit to less than 25% of the rated trip current.

What they are saying is that if an RCD, or GFCI for that matter, is protecting a circuit that "normally" has a leakage current that is too close to its trip point then it will be more susceptible to nuisanace tripping.

 

[electrics]

yes u are right indeed but i had it as a file downloaded not from webpage, thank u it is now very clear to me.also can u say anything about the formula at the last page?
it says In = kcxku (In1+In2+In3+In4) and it is not saying what is kc and ku can u say ?

 

[electrics]

ı couldnt find what they mean, pls check the document out, the final page....

 

[ELA]

yes u are right indeed but i had it as a file downloaded not from webpage, thank u it is now very clear to me.also can u say anything about the formula at the last page?
it says In = kcxku (In1+In2+In3+In4) and it is not saying what is kc and ku can u say ?

The only thing I can say about that equation is that it appears to have some unknown "konstants" applied.

Are you doing a design that requires such a calculation or asking just because? Sorry but I do not know what the constants may be.