The Siemens SENTRON 3VM9908-0BB15 is an undervoltage release accessory designed for 3VM molded-case circuit breakers up to 630 A. It operates on a 220-230 V DC control supply and trips the breaker when control voltage drops below the dropout threshold — standard practice for preventing motor restart after a power loss, or for emergency-stop circuits that need a fail-safe open on loss of control power.
What the ratings mean for fit
The release is rated for a rated insulation voltage Ui of 690 V, meaning the internal clearances and creepage distances are certified for 690 V line-to-line — matching the insulation level of the 3VM breaker itself. Overvoltage category III and pollution degree 3 place it in the industrial fixed-installation class (per IEC 60947-1), suitable for distribution panels where transient overvoltages and conductive dust are expected. The 4 kV surge voltage resistance confirms it will withstand the 4 kV impulse test required for category III equipment at 230/400 V mains. Power consumption max 2.5 W DC — the control transformer or power supply feeding this release must be sized to cover that continuous draw. Wire stripping length 10 mm (0.4 in) for the control terminals; standard ferrule or solid copper, no special crimp tool needed.