Time Mark Corporation A257B-480VAC 3Ph Power Monitor

The Time Mark A257B-480VAC 3-Phase Power Monitor is a solid-state three-phase monitoring relay that continuously supervises 480 VAC power systems for phase loss, phase reversal, and undervoltage conditions to protect motors and industrial equipment from damaging power abnormalities. Designed for Wye or Delta configurations without requiring a neutral, it automatically de-energizes its output relay whenever faults are detected, helping prevent motor damage and unplanned downtime. Specifications include nominal voltage 480 VAC (phase-to-phase) with a voltage adjustment range of 380–480 VAC, 60 Hz, and monitoring functions for phase loss, phase reversal, and undervoltage detection. Output contacts are SPDT rated 10 A at 240 VAC resistive, with a power consumption of 3.7 W, a response time of 50 ms, repeat accuracy of ±0.1% of set point, and a dead band of approximately 2%. Reset is automatic, and mounting is via an 8-Pin Socket with TRIP and NORM LEDs for status indication. Wye/Delta compatibility is noted with no neutral required. Operating temperature ranges from -20°F to +131°F (-29°C to +55°C), and the enclosure is ABS plastic. Certifications include UL Recognized and CSA Certified. Common applications span three-phase motor protection, HVAC equipment, pumps, compressors, conveyors, and other industrial control systems. Common replacements include Time Mark A257BM-480VAC, A258B-480VAC, and B257B-480VAC.