The passenger compartment is the largest consumer of auxiliary energy in a vehicle. Heating and air conditioning operate at 3×400 V from a converter or the train busbar, passenger sockets at 230 V 50 Hz, and lighting, passenger information systems and chargers at 24 V or 110 V DC. The train busbar specified by UIC 552 carries 800 A at 1000 V 16⅔/50 Hz, 1500 V AC/DC or 3000 V DC, and coach converters must withstand overloads and short circuits on the load side.
Heating and air-conditioning circuits combine high power with frequent switching cycles - a natural application for solid-state relays with load monitoring. Passenger circuits are the only circuits in the vehicle directly accessible to the public: sockets, buttons, chargers and emergency-brake handles must withstand vandalism and misuse. In a modern vehicle, the emergency brake does not directly vent the main brake pipe - it sends a signal to the cab. Away from a platform, the system introduces a delay of 10 ± 1 s; during this time the driver can inhibit automatic braking and move the train out of a tunnel instead of stopping it in the worst possible location. Non-metallic materials in the passenger area are subject to EN 45545-2 with an HL level determined by the vehicle category and the tunnels on its route.
Equipment used in this area includes: solid-state relays and contactors for heating, ventilation and air conditioning, protection for 3×400 V and 230 V circuits, information pushbuttons and indicators, assistance-call buttons, USB and inductive chargers, seat-reservation systems, onboard printers, connectors and enclosures for onboard electronics.
Selection criteria for this area:
From the train bus supplied by the locomotive (according to UIC 552: 1000 V at 16⅔/22/50 Hz, 1500 V 50 Hz, 1500 V DC or 3000 V DC, up to 800 A) through the coach's own converter to 3×400 V, or in electric multiple units directly from the vehicle's static converters. The converter must withstand overloads and short circuits on the load side.
Heaters switch frequently and carry high current; a solid-state relay has no mechanical contacts to wear out, can switch at zero crossing and enables proportional control. In return, it requires cooling and a blocking-voltage rating with sufficient margin for onboard-network overvoltages.
In a conventional coach, a valve vents the main brake pipe and the train brakes immediately. In a modern vehicle, the handle may send only a signal to the cab. At a platform or during departure, braking occurs without delay. Away from the platform, the system waits 10 ± 1 s - during this time the driver may inhibit automatic braking to avoid stopping the train inside a tunnel.
A vehicle is approved for tunnel category A (up to 5 km) or B (over 5 km). Category B requires an active fire-suppression system and stricter material requirements under EN 45545-2; this affects the selection of enclosures, covers and pushbuttons in passenger areas.