I don't know what you are measuring but when I worked on high voltage switchgear the systems relied on an earth connection for fault detection, so even if your local earth is disconnected there will be enough of a path to earth to still detect faults. The connection may be via the armour of the supply cable or simply the neutral being earthed by multiple neighbors. Actually, what are you referring to as an "Earthing cable", I'm assuming the one that connects the neutral to earth via a ground spike, you?
Mike.