- Reaction score
- 2,853
I personally don't see any value in using the MCB max permitted Zs values when there is an RCD protecting the circuit. Following 411.4.204, table 41.5, and 643.7.1 (a) and (b) means that I don't have to provide a Zs value, either measured or calculated, to prove ADS, assuming I have confirmed continuity of CPC. It frees me up to focus on other parts of the testing.Well that’s the dilemma & some disagreement here… To be fair I’ve seen both measurements recorded on Certs… personally I prefer the Zs for the MCB, with the 1666 only for the MCB
While I agree that a Zs test might show a problem with a loose connection in the circuit, I find the results to be inaccurate when compared to a continuity test (particularly no trip tests and/or TT earthing). IMO, better to take an R1+R2 reading, which should give a more accurate picture of the circuit's health.
EDIT: it also cuts down on the amount of live testing