Hi Andy, Yes!!!!! That is EXACTLY What i mean!!
In 7671 they have a table where RCBO's are lumped in with RCD's and it says underneath, something about the table gives the max Zs for the overcurrent part of the RCBO to operate.
Yes, the RCD bit might well operate at very low currents with a much higher Zs, [and so protect from shock to some degree] but there seems to me, that this may well give rise to a large "central" area, where NEITHER "half" of the device will operate within the required times.. Fault current not enough to operate the OCPD in the required time, but enough to cause sufficient volt drop across the supply to stop the RCBO from operating..
I might be completely wrong, but I think i am not.... Why else would they have lumped the RCBO's in with MCB's [same Zs values], in a section devoted to ADS....
john...
Hi Steve, the point i am making is, so far as i can see, an RCBO needs a supply voltage to operate, it is "voltage dependant". When a fault occurs, the supply voltage will drop much quicker than the RCBO can react. By the time this happens, there is not enough voltage to operate its internal electronics, and might as well not even be there.
An "ordinary" RCD, so far as i know, is "voltage independant" and would operate at any level of mains voltage... Rather better...
john...
In 7671 they have a table where RCBO's are lumped in with RCD's and it says underneath, something about the table gives the max Zs for the overcurrent part of the RCBO to operate.
Yes, the RCD bit might well operate at very low currents with a much higher Zs, [and so protect from shock to some degree] but there seems to me, that this may well give rise to a large "central" area, where NEITHER "half" of the device will operate within the required times.. Fault current not enough to operate the OCPD in the required time, but enough to cause sufficient volt drop across the supply to stop the RCBO from operating..
I might be completely wrong, but I think i am not.... Why else would they have lumped the RCBO's in with MCB's [same Zs values], in a section devoted to ADS....
john...
Hi Steve, the point i am making is, so far as i can see, an RCBO needs a supply voltage to operate, it is "voltage dependant". When a fault occurs, the supply voltage will drop much quicker than the RCBO can react. By the time this happens, there is not enough voltage to operate its internal electronics, and might as well not even be there.
An "ordinary" RCD, so far as i know, is "voltage independant" and would operate at any level of mains voltage... Rather better...
john...
