RCD Tripping

[bloxy]

JI don't really understand this, because even if the switch is ON or OFF, without an Oven connected how would the RCD know there was a fault? Does current flow and is it detected when the switch is ON even if nothing is connected?

Normally no, but since it trips when the switch is on and there is nothing connected at the other end there must be some leakage between the conductors in this cable which produces the fault condition that is detected by the RCD. For example, there could be nail or something through the cable causing an intermittent fault between live conductor and cpc earth (that's why it doesn't occur immediately) a small current flows through the live and returns via the cpc earth and there is no current on the neutral, voilà the RCD trips .