Siemens 3RV2042-4FB10 SIRIUS 3RV2 motor starter protectors. Siemens 3RV2042-4FB10 is the exact printed commercial reference for a motor protection circuit breaker in the SIRIUS 3RV Motor Protection range. Siemens' official product description is: Circuit breaker size S3 for motor protection, Class 20 A-release 28...40 A N-release 520 A screw terminal Increased switching capacity 100 kA.