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ABB M-EFS.2S Voltage Monitoring Relay 

1. Key Parameters

• Product Model: M-EFS.2S
• Product Type: Voltage monitoring relay (overvoltage/undervoltage/voltage imbalance protection)
• Core Function: Monitors AC voltage for anomalies; triggers protective actions (load disconnection, alarm) when voltage exceeds/falls below preset thresholds or imbalance exceeds limits
• Electrical Specifications:
  • Input Voltage Range:
    • Single-phase: 100V AC~240V AC (50/60Hz)
    • Three-phase: 380V AC~480V AC (50/60Hz)
  • Protection Modes:
    • Overvoltage (U>): Adjustable threshold (105%~130% of rated voltage)
    • Undervoltage (U<): Adjustable threshold (70%~95% of rated voltage)
    • Voltage Imbalance (ΔU): Adjustable threshold (2%~15% of average phase voltage; three-phase only)
  • Response Time: ≤200ms (for overvoltage/undervoltage); ≤500ms (for voltage imbalance)
  • Hysteresis: Adjustable (2%~10% of set threshold; prevents frequent switching from minor voltage fluctuations)
  • Output Configuration: 1× SPDT (Single Pole Double Throw) relay contact
    • Rated Output Current: 10A (resistive load, 230V AC); 5A (inductive load, 230V AC)
    • Maximum Switching Voltage: 250V AC / 30V DC
  • Power Supply: Derived from monitored input voltage (no external power required)
  • Power Consumption: ≤3VA (at rated voltage)
• Mechanical Specifications:
  • Housing Type: DIN rail-mounted (standard 35mm DIN rail per EN 60715)
  • Dimensions (W×H×D): 22.5mm × 85mm × 65mm (1-module width; saves space in control cabinets)
  • Terminal Type: Screw terminals (accepts 0.5mm²~2.5mm² copper conductors)
  • Weight: Approximately 120g
  • LED Indicators:
    • Power (PWR): Green (relay energized/monitoring active)
    • Overvoltage (U>): Red (overvoltage detected)
    • Undervoltage (U<): Red (undervoltage detected)
    • Imbalance (ΔU): Red (voltage imbalance detected; three-phase only)
• Environmental Ratings:
  • Operating Temperature Range: -25℃~+70℃ (-13℉~158℉)
  • Storage Temperature Range: -40℃~+85℃ (-40℉~185℉)
  • Humidity Tolerance: ≤95% RH (non-condensing, 40℃)
  • Vibration Resistance: 10~500Hz, 2g acceleration (IEC 60068-2-6; no false triggering)
  • Shock Resistance: 30g acceleration (11ms duration, IEC 60068-2-27; maintains calibration)
• Compliance Standards: IEC 61812-1 (voltage monitoring relays), EN 60947-5-1 (control circuit devices), UL 508 (industrial control safety), CE (EU safety & EMC directives)

2. Key Features

• Multi-Function Voltage Protection: Integrates overvoltage, undervoltage, and voltage imbalance protection in one compact unit—eliminating the need for separate relays and reducing cabinet space and installation costs.
• Dual-Phase Compatibility: Works with both single-phase (100V~240V AC) and three-phase (380V~480V AC) networks, making it versatile for residential, commercial, and industrial applications (e.g., single-phase HVAC, three-phase motor control).
• Adjustable Thresholds & Hysteresis: Customizable overvoltage/undervoltage limits (105%~130% Ue / 70%~95% Ue) and imbalance thresholds (2%~15%) allow tailoring to specific equipment requirements (e.g., sensitive electronics vs. heavy motors). Hysteresis prevents "chattering" from minor voltage fluctuations.
• Fast Response Time: ≤200ms reaction to over/undervoltage and ≤500ms to imbalance ensures rapid load disconnection—critical for protecting sensitive equipment (e.g., PLCs, variable-speed drives) that cannot withstand prolonged voltage anomalies.
• Self-Powered Design: Derives power directly from the monitored voltage, eliminating the need for an external power supply. Simplifies wiring and ensures the relay remains active even if auxiliary power fails.
• Intuitive Status Monitoring: LED indicators for power, overvoltage, undervoltage, and imbalance provide clear visual feedback on circuit conditions—enabling quick troubleshooting during faults (e.g., identifying whether a trip was caused by overvoltage or imbalance).
• Industrial-Grade Durability: Flame-retardant thermoplastic housing (UL94 V-0) and robust internal components withstand extreme temperatures (-25℃~+70℃), vibration, and humidity—reliable for harsh environments like manufacturing plants, mining sites, and outdoor substations.

3. Application Fields

• Motor Protection: Installed in three-phase motor control circuits (e.g., pumps, fans, conveyors) to disconnect power during voltage imbalance (a leading cause of motor overheating and winding damage) or over/undervoltage (which reduces motor efficiency and lifespan).
• HVAC Systems: Protects single-phase (residential AC units) and three-phase (commercial chiller systems) HVAC equipment from voltage fluctuations—preventing compressor burnout and ensuring consistent temperature control.
• Industrial Automation: Monitors voltage for PLCs, variable-speed drives (VSDs), and instrumentation circuits—safeguarding sensitive automation components from voltage spikes (e.g., from nearby motor startups) or dips (e.g., grid load surges).
• Commercial Building Electrical Systems: Used in panelboards for offices, retail stores, and hotels to protect lighting, elevators, and office equipment—avoiding costly downtime from voltage-related equipment failures.
• Renewable Energy Inverters: Monitors grid voltage for residential/commercial solar inverters—disconnecting the inverter from the grid during overvoltage (to comply with grid codes) or undervoltage (to protect inverter electronics).
• Medical Facilities (Non-Critical Areas): Protects non-patient-care equipment (e.g., office computers, laundry machines) in hospitals and clinics—ensuring basic facility operations remain uninterrupted during minor voltage anomalies.
• Agricultural Equipment: Installed in three-phase irrigation pumps and farm machinery—withstanding dust and temperature variations while protecting equipment from rural grid voltage instability.

4. Precautions

• Input Voltage Compatibility: Ensure the relay’s input voltage range matches the monitored circuit (single-phase 100V~240V AC or three-phase 380V~480V AC). Connecting to an incompatible voltage (e.g., 480V AC to a single-phase-configured relay) will destroy internal components.
• Threshold Calibration: Set overvoltage/undervoltage/imbalance thresholds per the connected equipment’s specifications (refer to the equipment’s manual for safe voltage ranges). Overly sensitive settings cause nuisance tripping; overly lenient settings compromise protection.
• Wiring Safety:
  • For three-phase applications, connect all three phases to the relay (do not omit a phase)—missing a phase causes incorrect imbalance detection.
  • Use copper conductors (0.5mm²~2.5mm²) and tighten terminal screws to 0.6~0.8N·m to avoid loose connections (which cause voltage measurement errors).
  • Separate relay wiring from high-power cables (≥20cm spacing) to minimize EMI interference with voltage sensing.
• Output Load Compatibility: Do not exceed the relay’s maximum output current (10A resistive / 5A inductive). For higher-load applications (e.g., large motors), use the relay to control a contactor (instead of directly switching the load) to prevent relay contact damage.
• Environmental Protection:
  • Install in enclosed control cabinets to shield from dust, moisture, and direct sunlight. Avoid exposure to corrosive gases (e.g., sulfur dioxide in industrial zones) or temperatures beyond -25℃~+70℃.
  • In outdoor applications (e.g., solar inverters), use weatherproof enclosures with proper ventilation to prevent overheating.
• Maintenance Checks: Inspect quarterly:
  • Verify LED status (GREEN = normal monitoring; no red LEDs illuminated).
  • Test protection functions by simulating voltage anomalies (use a variable voltage source) to confirm the relay triggers the output signal.
  • Clean terminals with a dry cloth to remove dust or corrosion—accumulated debris can cause poor voltage sensing.
• Fault Troubleshooting: If the relay trips unexpectedly:
  • Check the grid voltage (use a multimeter) to confirm if the anomaly was real (e.g., grid overvoltage) or a relay error.
  • If no voltage anomaly exists, recalibrate the thresholds or test the relay with a known good voltage source—replace the relay if it fails calibration
• 

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