METHOD FOR DETERMINING TRACE BETWEEN ACCESSIBLE CLAMP OR PLACE OF EARTH FAULT AND SUPPLY CLAMP RESPECTIVELY KNOWN CLAMP OF A POWER LINE UNDER VOLTAGE AND/OR DETERMINING PHASE OF THE GIVEN WIRE ON WANTED PLACE OF THE WIRE SECTOR BETWEEN ACCESSIBLE CLAMP AND SUPPLY CLAMP, AS WELL AS APPARATUS AND TWO-TERMINAL NETWORK OF PERIODICALLY VARIABLE IMPEDANCE TO THE PURPOSE FOR IMPLEMENTING SAID METHOD