ST420B3 Microprocessor-Based Circuit Protection Device

This is a high-precision multifunctional device integrating electrical measurement and comprehensive protection functions for industrial power distribution systems. It features wide-range voltage and current monitoring, strong overload withstand capability, fast signal response, and reliable environmental adaptability. With standard industrial communication and excellent EMC performance, it ensures stable power system operation and accurate data acquisition for industrial power monitoring and fault protection scenarios.

Key Applications

Industrial Power Distribution Cabinets: Real-time monitoring of three-phase voltage, current, power, energy and harmonic parameters, with reliable overcurrent and overvoltage protection for power distribution equipment. Leakage and Earth Fault Protection: Supports zero-sequence leakage current detection and protection to avoid insulation failure and earth faults in power circuits. Automatic Industrial Control: Adopts optical-isolated digital input and high-speed relay digital output for on-site signal acquisition and interlock control; 4~20mA analog output transmits measured values to remote control systems. Remote Power Monitoring Platform: Equipped with Modbus-RTU communication to realize stable data upload for industrial SCADA and power management systems.

Technical Specifications

Operating Temperature -10℃ ~ +55℃ Storage Temperature -25℃ ~ +70℃ Protection Class IP20 Auxiliary Power 85~264VAC / 90~300VDC Rated Frequency 50/60Hz Rated Voltage 380V Current Range Built-in ranges up to 400A; external CT expandable up to 820A Digital Output Contact Rating 7A 250VAC / 30VDC resistive load Analog Output 4~20mA, Max load resistance ＜600Ω Measurement Accuracy Current/Voltage/Leakage Current ±1%; Power/Energy ±2%; Analog output ±0.5% Protection Setting Error ±3% Communication Interface RS-485, Modbus-RTU, baud rate 9600/19200bps

Product Highlights

Wide operating temperature range, stable operation at altitude up to 3000m, no condensation or icing inside the unit Strong overload withstand capacity for current and voltage loops with continuous and short-time overload capability High-precision measurement covering electrical parameters, leakage current and voltage/current harmonics Optically isolated digital input and fast response relay output for reliable signal control Superior insulation performance and mechanical resistance against vibration, shock and bump Full EMC compliance with high anti-interference performance for industrial electromagnetic environments

Standards Compliance

GB/T 11287 — Environmental testing for vibration GB/T 14537 — Environmental testing for shock and bump GB/T 14598.26 — Electromagnetic compatibility for measuring relays and protection equipment