The functions of 2 and 3 element type are almost same, but since theneutral pole (3/L2, 4/T2) of 3-pole 2-element type is connected inside, itis not possible to use in the delta phase to add the applicable capacity.Moreover, you need to install a disconnecting equipment at power supplyside and disconnect for maintenance all the time, since the load side isalways same potential as the power supply side.