What it is and where it goes
The Siemens SENTRON 3VA9387-0TB50 is a 24 V module designed as an accessory for 3VA2 molded-case circuit breakers in the 400 A, 630 A, and 1000 A frame sizes. It mounts in the right switch pocket of the breaker and provides four slots for communication and measurement functions. The module draws a maximum of 0.1 A from the 24 V supply and dissipates 2.4 W. It powers the electronic trip unit and communicates with the breaker's internal systems, but it does not handle motor-drive, function-module, or residual-current communication, nor does it detect switch position (On/Off/Tripped).
Fit and environment
Physical footprint is 33 mm deep, 29 mm wide, and 63 mm tall. The module is rated IP20 per IEC 60529, meaning it is protected against solid objects larger than 12 mm but not against moisture — suitable for dry indoor panel environments. It carries pollution degree 3 (conductive pollution or dry non-conductive pollution that becomes conductive due to condensation) and overvoltage category I. Operating temperature range spans -40 °C to 80 °C, which covers most industrial enclosures. Supply voltage tolerance is ±20 %.