3-Phase Voltage Monitor Relay 190-480V Littelfuse 201A Phase Loss 8-Pin

The Littelfuse 201A is a three-phase, auto-ranging, dual-range voltage monitor relay that protects 190–480VAC, 50/60 Hz motors of any size. It provides a user-selectable nominal voltage setpoint and automatically selects between the 200V and 400V ranges, saving setup time. This microcontroller-based voltage and phase-sensing unit constantly monitors three-phase voltages to detect harmful power line conditions — when a fault is detected, the output relay deactivates after a set trip delay, then reactivates once conditions return to acceptable levels after a restart delay. Advanced single-LED diagnostics use color and light patterns to distinguish faults from normal operation.
 
Key Specifications
Type: 3-Phase Voltage / Phase Monitor Relay
Voltage Range: 190–480VAC (auto-ranging, dual-range)
Frequency: 50/60 Hz
Voltage Setpoint: User-selectable nominal
Protection: Phase loss/single-phasing, phase reversal, voltage unbalance, low voltage (high voltage optional)
Diagnostics: Single-LED (normal, restart delay, reverse-phase trip, unbalance/single-phase trip, high/low voltage trip)
Configuration: 8-Pin
Mounting: DIN Rail or Surface Mount
Circuitry: Proprietary microcontroller-based
 
Ideal for protecting fan motors, air conditioners, compressors, heat/well/sump pumps, and small conveyor motors against costly damage from phase loss, voltage imbalance, and abnormal power line conditions.