changing single socket to double,used check plug which showed phase /neutral reversal.took bell wire from line wire at ccu to line at socket & continuity verified.did same with neutral wire & continuity OK.decided to reverse wires at socket then check plug showed as open earth.old house with red/black wiring.also cooker hood has been added at some stage on this circuit.no problem with other sockets on the circuit.any kind gent out there for comments/advice