In have just tried to perform a RCD test on a split load domestic board, the meter didn't trip the RCD on with of the RCD's, at either a point in the property or at the board, the Ze is good, the meter display showed the voltage in large on the bottom reading, then in the small display above that normally shows the frequency had the letters LPE I have tried the meter on another RCD and all was fine, can anyone shed any light on this please?