- Reaction score
- 2,833
Why? Because that is the maximum Zs for the circuit. The RCD doesn't know or care whether the earthing arrangement is TN or TT, or if you prefer the values for MCB, it's going to trip anyway, and that is its max Zs.Agree so why would anyone wanna put 1666 in the column regarding TN Systems
Especially when the actual measured Zs is going to be a low Ohm reading
Also: Because where a circuit is protected by an RCD, there is no need to provide a Zs reading, either measured or calculated. Once you have proved that the RCD works, and that the CPC is continuous by either R2 or R1+R2, then you have met disconnection times.