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If you meet ADS by OCPD then you meet thermal constraints. If you meet ADS by relying on an RCD then you may well not meet thermal constraints for L-N by the OCPD which is still covering that.
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Correct, which is why I said earlier on that all aspects of the regs still need to be adhered to.If you meet ADS by OCPD then you meet thermal constraints. If you meetr ADS by relying on an RCD then you may well not meet thermal constraints for L-N by the OCPD which is still covering that.
Correct, which is why I said earlier on that all aspects of the regs still need to be adhered to.
I grant you that some people may not check various aspects of the regs, usually because "it's always been OK in the past" but I think that happens all the time, I come across so much work where the person installing hasn't thought about it one bit - basically it's never designed, just installed.
Not always. With MCBs, the let through energy tends to increase with increasing fault current. So the most onerous part of the circuit for thermal constraint is close to the origin, where ADS is assuredIf you meet ADS by OCPD then you meet thermal constraints.
Not always. With MCBs, the let through energy tends to increase with increasing fault current. So the most onerous part of the circuit for thermal constraint is close to the origin, where ADS is assured
I don't think there any additional considerations for using manufacturer's data, it just replaces the I2t in the equation AFAIK.Generally it does work out with MCB's if you are operating with pfc's withing the breaking capacity of the device. At least it always has in the real world scenarios I have applied it. There is also the other variable of manufacturers data where you can go with faster times than the 0.1s in the regs which I believe has additional considerations attached that I can't remember what they are?
I think the adiabatic appears only to be related to protective conductors in the regs as it's included in that section and the CPC is usually the smallest (or at least the same size).I don't think there any additional considerations for using manufacturer's data, it just replaces the I2t in the equation AFAIK.
Using, for example, data for a 32A Hager B curve, and using a 1mm2 CPC, it is possible to fall foul for fault currents of ~3kA or greater, and for higher fault currents for lower rated MCBs. So potentially a problem for old ring finals wired with 1mm CPCs, or other such circuits.
Interesting to note that the adiabatic equation only seems concerned with protective conductors, as far as the regs are concerned, as far as I can tell anyway
Thanks JulieYes, time delayed rcd on distribution circuits, standard rcd on final circuits - rcds as fault protection.
No need to convert to TT
leave it as TN-C-S and you can still use 0.4s / 5s but add rcd as fault protection where required.
So if the cable from the meter location to cu fails to operate in 5s due to fault, add a time delayed rcd.
If any final circuit fails to operate in 0.4s due to fault add a standard rcd.
If a circuit will operate within these times, then a rcd is not required for fault protection, but may be required for additional protection.
It was on the IET forum about why we should not use adiabatic for fault currents operating devices <0.1S or >5S. I couldn't remember but just found it again on there.I don't think there any additional considerations for using manufacturer's data, it just replaces the I2t in the equation AFAIK.
Using, for example, data for a 32A Hager B curve, and using a 1mm2 CPC, it is possible to fall foul for fault currents of ~3kA or greater, and for higher fault currents for lower rated MCBs. So potentially a problem for old ring finals wired with 1mm CPCs, or other such circuits.
Interesting to note that the adiabatic equation only seems concerned with protective conductors, as far as the regs are concerned, as far as I can tell anyway
Interesting to note that the adiabatic equation only seems concerned with protective conductors, as far as the regs are concerned, as far as I can tell anyway
My bad, it isn't only concerned with protective conductors:I think the adiabatic appears only to be related to protective conductors in the regs as it's included in that section and the CPC is usually the smallest (or at least the same size).
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