The Siemens 3RV1938-1A is a SIRIUS disconnector module designed for Size S2 motor circuit breakers. It provides a visible isolating distance and can be locked in the disengaged position, giving a positive mechanical disconnect for safe maintenance access.
The 3RV1938-1A is a phased-out product. The official Siemens successor is the SIRIUS 3RV2 series, with the preferred replacement order code 3RV2938-1A.
The visible isolating distance means the module creates a physical air gap you can see when disengaged — a requirement for lockout/tagout on motor circuits. The lockable disengaged position lets you secure the disconnect with a padlock, meeting OSHA-style isolation needs. Size S2 tells you it mates with S2-frame Siemens breakers like the 3RV20 series; the 55 mm width matches the standard S2 module pitch, so it drops into the same DIN-rail slot as the breaker it serves.
Deployment Context
Use it upstream of the breaker as a service disconnect — the visible gap confirms the circuit is dead before you open the panel. The lockable handle accepts standard padlock hasps for group lockout procedures.