The Siemens 3VA9987-0TA20 is a SENTRON COM100 breaker data server — the communication gateway for a single 3VA molded-case circuit breaker. It sits in the fixed switchboard inside enclosed rooms (IP20 per IEC 60529) and occupies 5 modular width units on the DIN rail. The 90 x 90 x 33.5 mm footprint fits the standard panel cutout for 3VA accessories.
Fieldbus and data exchange
Three protocol stacks on one module: PROFIBUS DP, PROFINET IO, and Modbus RTU. The Fast Ethernet interface (100 Mbit/s, RJ45) supports auto-MDI(X) and a serial gateway for legacy slaves. Up to 5 active Ethernet connections can be open simultaneously. The Modbus RTU interface uses screw-type terminals for the supply voltage input. Data exchange with the electronic trip unit is bidirectional — the COM100 reads switch position (On, Off, Tripped) and can pull metering values from the breaker's trip unit. The total daisy-chain length for the circuit breaker communication system is 20 m, with 2 bus termination connectors supplied.
Power budget and mounting
Draws 1.1 A maximum from the 24 VDC supply (SELV / PELV, operating resource protection class III per IEC 61558). Power dissipation is 5 W at rated load — factor that into the enclosure thermal budget. Mounting position is any orientation; the removable/pluggable screw-type terminals simplify pre-wiring before the module is snapped onto the DIN rail. The module connects directly to one 3VA breaker via a dedicated interface. An expansion interface is available for additional communication modules. The electronic trip unit power supply is fed through the same connection.