I think this has been covered once before, but one of the current IET publications shows on the schedule of test results Max Zs as 1666 when protected by RCD (possibly RCBO as well) even when having a TN-C-S connection. I wondered what was the current opinion on this.
Certainly the maximum Zs for a 30mA RCD protected circuit is nominally 1667 Ohms, but it would be unwise to approach this figure, in the same way as TT earth electrode resistances. Really this column is only there to make sure that the Zs has been checked for the circuit, for whatever CPD is fitted. In this case it is an RCD and therefore the "magic" 1667 Ohms is the number to fill in, or some other one if the RCD has a different delta In value.
Certainly the maximum Zs for a 30mA RCD protected circuit is nominally 1667 Ohms, but it would be unwise to approach this figure, in the same way as TT earth electrode resistances. Really this column is only there to make sure that the Zs has been checked for the circuit, for whatever CPD is fitted. In this case it is an RCD and therefore the "magic" 1667 Ohms is the number to fill in, or some other one if the RCD has a different delta In value.
