The Siemens SENTRON 3VA9187-0TB50 is a 24 V module designed as an accessory for the 3VA2 molded case circuit breaker family, specifically the 100, 160, and 250 A frame sizes. It occupies the right switch pocket of the breaker, adding communication and measurement functions via its four slots. This is the part that brings remote monitoring and control capability to a 3VA2 installation — without it, the breaker is a standalone overcurrent device.
Mounting is straightforward: the module snaps into the right-side pocket of the 3VA2 breaker. No DIN rail or additional bracket is needed — the breaker itself is the mounting surface. The module draws a maximum of 0.1 A from the control supply and dissipates 2.4 W, so it adds negligible thermal load to the enclosure. Power is delivered via screw-type terminals at the inputs for supply voltage, with a 20% symmetrical tolerance on the control feed voltage — meaning a nominal 24 VDC supply can sag to 19.2 V or rise to 28.8 V without dropping the module.
Overvoltage category I means it is intended for circuits connected to the mains via a transformer or similar isolation — not for direct connection to the utility supply. Operating resource protection class III per IEC 61558 means the module is supplied from a safety extra-low voltage (SELV) source — the 24 V supply must come from a transformer or power supply that provides SELV output. The module also provides power to the electronic trip unit of the 3VA2 breaker, which is its primary function: it keeps the trip unit alive for communication and metering even when the main breaker contacts are open.