What is a rotating field control test plug?

Three-phase sockets must be connected in such a way that there is a clockwise rotating field. The rotating field control test plug differs from normal plugs due to its transparent housing. By means of two control lamps inside the housing, this plug indicates whether the field is rotating in a clockwise or anticlockwise direction and checks that all 3 phases are present. This shows the direction of the rotating field. If the rotating field is correct, the green lamp lights up; if the rotating field is incorrect, the red lamp lights up and if a phase is missing, both lamps light up. More information