Beckwith M‑0389 Voltage Verifier

The Beckwith M‑0389 is a solid‑state voltage verifier relay designed to provide under‑voltage and over‑voltage detection for single‑phase or three‑phase AC power systems. It continuously monitors the voltage and operates when the measured value falls outside the programmed voltage window. The relay is used to alarm, trip, or initiate control actions in response to abnormal voltage conditions, protecting equipment from undervoltage (brownouts, loss of source) and overvoltage (regulator failure, load rejection).

Operation and Settings

The M‑0389 features independent adjustable setpoints for undervoltage and overvoltage, each with its own time delay. The undervoltage pickup is typically adjustable from 0.5 to 120 VAC, and the overvoltage pickup from 1 to 300 VAC. Time delays are adjustable from 0.1 to 30 seconds, allowing coordination with other protection devices. The relay includes a built‑in window comparator with hysteresis to prevent chattering near the setpoint. A front‑panel potentiometer enables easy adjustment of setpoints and delays.

Key Features

Independent undervoltage and overvoltage elements. Adjustable pickup and time delay for each element. LED indicators for voltage status and trip conditions. Output contacts: 2 Form C (one for undervoltage, one for overvoltage), rated 5 A at 250 VAC. The relay is housed in a rugged metal enclosure suitable for panel mounting. It operates from a wide range of DC or AC control voltages.

Technical Specifications

Voltage input: 1‑300 VAC, 50/60 Hz. Pickup accuracy: ±2% of setting. Time delay accuracy: ±3% or 50 ms. Output contacts: 2 Form C, 5 A at 250 VAC. Power supply: 24‑250 VDC or 120‑240 VAC. Burden:<5 VA. Operating temperature: –20°C to +65°C. Meets IEEE C37.90 surge withstand.

Applications

The M‑0389 is used in generator control panels, automatic transfer switches, motor control centers, and transformer monitoring systems. It provides voltage verification for automatic transfer schemes and alarms for maintenance personnel.

Installation and Commissioning

Mount the relay in a panel cutout. Connect voltage sensing leads and control power. Commissioning involves setting the undervoltage and overvoltage pickup values and time delays, then testing with a variable AC source.

Reliability and Quality

Beckwith’s M‑0389 is built with solid‑state technology and conformal coating for environmental resilience.

Conclusion

The Beckwith M‑0389 voltage verifier provides reliable under/over voltage detection for power system protection and control applications.