The circuit breaker incoming/outgoing panel is the feeder type in which protection is performed at the panel itself. The arrangement runs from the disconnector on the busbar side, through the circuit breaker and the current transformer, to the earthing switch on the cable side.
The circuit breaker is the only device with the capacity to interrupt short circuit current, and it trips automatically on command from the protection relay. The current transformer supplies the measurement signal to that relay and is connected in series with the main circuit.
The duty of the busbar side disconnector is to isolate the circuit breaker from busbar voltage for maintenance. A disconnector cannot be opened on load; the sequence is always to open the circuit breaker first, then isolate with the disconnector, and only then earth.
Typical use: high power feeders, motor and transformer outgoing circuits, and distribution points requiring discriminative protection.
