Active and passive relates to whether the RCD drops out when power is lost. All RCDs in domestic consumer units are passive (latching) so they remain latched in the ON position regardless of a power failure. An active (Non-latching) RCD on the other hand unlatch to OFF on the loss of power and require resetting to ON when the supply is restored after the power cut; similar to a Direct On Line (DOL) motor starter. The active RCD is usually used for extension leads or outdoor equipment such as lawnmowers where unexpected restarting of electrical machinery or equipment could present a danger to the user after a power cut.
Most RCDs have electromagnetic mechanisms of some sort. Fully solid-state RCD designs do exist, however, they contravene BS7671:2008+A1:2011, 537.2.2.1 and therefore rarely seen or used in the UK.
