The Siemens 5SY6404-7 is a Circuit Breaker with 230/400VAC, 4A current, 4 poles, a DIN rail mount, and a C Characteristic curves at 6kA. It is designed to break or make an electrical circuit, preventing excess current to flow back into the circuit, protecting it from damage or overload. It also provides overload protection, short circuit protection, and interruption of the load current.