- Prior to 1998 all breakers were D curve.
- Since 1998 all single pole breakers have been changed to C curve.
- From 1998 to 2009 all double pole breakers were still D curve.
- Since 2009, all CE breakers (Single Pole, ND, RCD) have been C curve.
- C & D Curves are defined by a European Standard. A is the fastest curve, D is the slowest.
The curve letter describes the trip time/current for overcurrent tripping. It is an important parameter for installers.