Sorry if I am missing something, but the title says "Rcd Saves A Fencing Contractors Life"
If the cable is swa, and the armour was earthed, or even if it wasn't he was still using a battery operated saw which was probably plastic coated or plastic handle how did the rcd save his life?
If the armour was earthed, soon as he cut through that into one of the cores yes, the rcd would trip, but if he cut through the live and the armour the mcb would trip (Ok, with a bang but it was on the other side of the fence)