Product: Automatic Transfer Switch S3125C/4P and S3125D/4P Cable compatibility: 125A C type cable Models and difference: S3125C/4P: without RS485 communication interface S3125D/4P: with RS485 communication interface, supports ModbusRTU Why this product solves power continuity problems Ensures uninterrupted power by transferring loads between two power sources automatically. Integrates with generator controls and firefighting systems to protect critical loads and allow safe shutdowns. Flexible configuration for local control or remote monitoring and control when RS485 is required. Key features and functions Rated working current range: 16 A to 630 A, suitable for small to large power distribution systems. Three switch positions: Main, Standby, and Doubleoff for normal operation, backup connection, and emergency disconnection. Controller functions include overvoltage and undervoltage monitoring, overfrequency and underfrequency monitoring, and status LED indication. Firefighting linkage: passive input that forces the switch to Doubleoff when activated; passive feedback output provides confirmation to external fire systems. Generator control: dry relay contacts for generator start and stop with configurable start and stop delays; requires auxiliary DC24 V for generator delay functions. Communication (S3125D/4P only): RS485 port with ModbusRTU for remote signaling, remote measurement, remote control, and remote parameter adjustment. Signal outputs: active power indication outputs AC230 V, 0.5 A for external indicators. Auxiliary power input: accepts DC12 V or DC24 V for control logic and generator delay features. Signal interfaces are passive where specified, suitable for connecting to external relays and monitoring systems. Control terminal overview Power supply signal outputs: terminals 101 to 103 for source I indication and closing signals; terminals 201 to 203 for source II indication and closing signals. Note: terminals 101 N1 and 201 N2 are controlled neutral lines for 3P products. Auxiliary power input: terminals 301 to 302, DC12 V or DC24 V. Firefighting linkage: terminals 401 and 402 passive input for normally open contacts; terminals 403 and 404 passive output for feedback signal when switched to Doubleoff. Generator signal output: terminals 501 to 503 passive contacts for generator start/stop control. Operating and storage conditions Ambient operating temperature: 5 C to +40 C; 24 hour average should not exceed +35 C. Relative humidity: up to 50 percent at +40 C; higher relative humidity allowed at lower temperatures, for example up to 90 percent at +25 C. Take measures for occasional condensation. Installation altitude: up to 2000 m. Pollution degree: level 3. Transportation and storage temperature: 25 C to +55 C, shortterm up to +70 C within 24 hours. Protect the product from rain and snow during transport. Typical applications Hospital power backup systems where uninterrupted supply is critical for life support and emergency equipment. Commercial facilities such as shopping malls and banks that need reliable automatic transfer between utility and generator power. Industrial sites and rise buildings integrating diesel generators and firefighting systems for coordinated emergency response. What makes it stand out Wide current range for flexible deployment across many electrical systems. Clear firefighting and generator control interfaces for safe, coordinated operation. Optional RS485 communication for remote monitoring and control when integration with building management or generator control systems is required. Note: If installation environment differs from the stated operating conditions, provide details to the system designer or installer.