Hello people 1st post. I am a apprentice and I would like to clear up something. RCDs do they need cpc to operate ? As if there is no earth faulth path for the imbalance to flow down then an imbalance cant be detected ? The reason I ask this is because I went to a job with the person I worked with and there was a fault on a lighting circuit, established what circuit it was. Now when he energised that circuit after about ten seconds the rcd would trip. There was about 12 fittings on that circuit all cat II. What he done was disconnect the cpc at the board and then energise the circuit, and then the rcd did not trip, whilst it was like this he found the fitting which had a ballist inside sizzling. my question is why did the rcd not trip if it runs on an imbalance fault between line and neutral, because the cpc was disconnected. Are Rcds pointless without a good earth path for the current to flow down so the imbalance is detected. All your thoughts and views will be appreciated. Thank u in advance.