●are characterised by identical tripping and resetting points.

●The displacement speed of the moving contacts is equal, or proportional, to the speed of the operator (which must not be less than 1 m/s = 6 m/minute).

●The opening distance is also dependent on the distance travelled by the operator.

Example: N/C + N/O break before make
A - Maximum travel of the operator in millimetres or degrees.
B - Tripping and resetting travel of contact 21-22.
C - Tripping and resetting travel of contact 13-14.
P - Point from which positive opening is assured