Time Mark Corp. Model 257BM 3-Phase Universal Phase Monitor w/Manual Reset

257BM Series*

The Time Mark Model 257 continuously monitors 3-phase power lines for abnormal conditions. When properly adjusted, the Model 257 monitor will detect phase loss on a loaded motor even when regenerated voltage is present. This device consists of a solid-state voltage and phase-angle sensing circuit, driving an electromechanical relay. When correct voltage and phase rotation are applied, the internal relay will energize. A fault condition will de-energize the relay. When the fault is corrected, the monitor will automatically reset (Model 257B) or need to be manually reset (Model 257BM).

The Model 257 does not require a neutral connection and can be used with Wye or Delta systems. Voltage ranges are sufficiently wide to allow for proper adjustment to existing conditions. Both TRIP and NORM condition indicators are provided to aid in adjustment and system trouble-shooting.


  • Detects phase loss, phase reversal and low voltage
  • 50Hz, 60Hz and 400Hz models available
  • Manual reset
  • 5 Year unconditional warranty
More Information
Display No
Features Manual Reset
Manufacturer Time Mark Corporation
Measurement Phase Loss Sensing, Phase Sequence Sensing, Under Voltage Sensing
Type Phase Monitor
Additional Skus B257BM, 257BM, A257BM, EX257BM, B257BM-400HZ, 257BM-400HZ, EX257BM-415V
Additional Details

*Pricing & appearance may vary based on configuration!* Please configure product above.

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