Time Mark Corporation A257B Three-Phase Monitor

Description:

The Time Mark Corporation A257B 3-Phase Monitor is designed to continuously monitor three-phase power systems for phase loss, phase reversal, and undervoltage conditions, helping protect motors and industrial equipment from electrical faults. Commonly installed in motor control centers, HVAC systems, pumps, compressors, conveyors, and manufacturing equipment where dependable three-phase power monitoring is essential. Maintenance teams, OEMs, and system integrators use the A257B for replacement, repair, retrofit, and preventive maintenance to improve equipment reliability and reduce unplanned downtime.

Applications:

The Time Mark A257B is a solid-state three-phase monitoring relay that continuously supervises Wye or Delta power systems without requiring a neutral connection and automatically de-energizes its output relay whenever phase loss, phase reversal, or undervoltage conditions are detected. It is widely used in industrial automation, motor control panels, HVAC equipment, water and wastewater facilities, compressors, conveyors, and process machinery where reliable three-phase power monitoring helps prevent motor damage and production interruptions.

Technical Specifications:

• Manufacturer: Time Mark Corporation
• Manufacturer Part Number (MPN): A257B
• Product Type: 3-Phase Power Monitor Relay
• Series: 257 Series
• Nominal Voltage: 480 VAC (Phase-to-Phase)
• Voltage Adjustment Range: 380–480 VAC
• Frequency: 60 Hz
• Monitoring Functions: Phase Loss, Phase Reversal, Undervoltage Protection
• Output Contacts: SPDT, 10 A at 240 VAC Resistive
• Power Consumption: 3.7 W
• Response Time: 50 ms Dropout
• Repeat Accuracy: ±0.1% of Set Point
• Dead Band: Approximately 2%
• Reset: Automatic
• Mounting: 8-Pin Socket
• Indicators: TRIP and NORM LEDs
• Wye/Delta Compatible: Yes (No Neutral Required)
• Operating Temperature: -20°F to +131°F (-29°C to +55°C)
• Enclosure Material: ABS Plastic
• Certifications: UL Recognized, CSA Certified
• Application: Three-phase motor protection, industrial control systems, HVAC, pumps, compressors, conveyors, and process equipment.

Common Replacements:

• Time Mark A257BM
• Time Mark A258B
• Time Mark B257B