How should you choose between the K2CA-DO Over-Current Relay and K2CA-DO3 Over-Current Relay?

Select the model according to the Breaker's trip method.
K2CA-DO-[]: Current transformer secondary current tripping
K2CA-DO3-[]: Voltage, no-voltage, DC tripping

Note: The box "[]" in the model number is for the case code. The following three types are available.

D2: Square embedded pull-out type
F4: Compact square embedded type
R2: Compact round embedded type