In a residential distribution board, the bell transformer is often the last thing anyone thinks about — until the doorbell stops working. The 4AC3214-0 is a 14 VA unit from the SENTRON 4AC3 series that occupies just two modules on a DIN rail and delivers three selectable secondary voltages: 8 V for older mechanical chimes, 12 V for electronic gongs, and 24 V for door‑opener circuits. The key difference from a generic bell transformer is the integrated PTC thermistor. When a short‑circuit occurs — a chime wire pinched in a door frame, for example — the PTC heats up and limits the current, then resets itself once the fault is cleared. No fuse to replace, no call‑back for the electrician. At 64 mm high and 90 mm long, it fits comfortably into a populated board, and the screw terminals accept wires up to 2.5 mm².