Beckwith M‑0389 Voltage Verifier Relay

The Beckwith M‑0389 is a versatile voltage verifier relay that monitors single‑phase or three‑phase AC voltages and provides both under‑voltage (ANSI 27) and over‑voltage (ANSI 59) protection. It is used to detect abnormal voltage conditions and initiate alarms, breaker trips, or load shedding actions. The relay is widely applied in generator protection, transformer monitoring, and automatic transfer switch systems, offering adjustable setpoints and time delays for flexible coordination.

Measurement and Settings

The relay features independent undervoltage and overvoltage elements. Each element has its own pickup adjustment (undervoltage 0.5‑120 VAC, overvoltage 1‑300 VAC) and time delay adjustment (0.1‑30 seconds). The relay includes a built‑in hysteresis circuit to prevent chattering. A front‑panel potentiometer allows easy setting changes. LED indicators show voltage status and trip conditions.

Output Contacts

The relay provides two Form C output contacts: one for undervoltage trip and one for overvoltage trip. Each contact is rated 5 A at 250 VAC. A separate alarm contact can be used for remote annunciation.

Technical Specifications

Input voltage: 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. Operating temperature: –20°C to +65°C. Meets IEEE C37.90.

Applications

Used in generator control panels, automatic transfer switches, and motor control centers for undervoltage and overvoltage protection.

Installation and Commissioning

Mount in panel cutout. Connect voltage inputs and control power. Set pickups and time delays, then test with variable voltage source.

Conclusion

The Beckwith M‑0389 voltage verifier relay provides reliable, adjustable under/over voltage detection for power system protection.