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Thermistor Protection Unit - Dual

Two sets of Thermistors of different switching temperatures are connected to the Dual Thermistor Protection Unit, one set for Alarm and the other set for Trip. Normally a temperature difference between Alarm and Trip is 20-30°C. Each set of Thermistors consists of 3 Thermistors connected in series.

The relay gets actuated only when the ALARM and TRIP Thermistors are connected in parallel to TPU. When the ALARM Temperature is attained the ALARM changeover contacts are activated and then indication is obtained from TPU. The potential free ALARM contacts can be used for connecting to a indicating lamp or siren for annunciation.

If no corrective action is taken after the ALARM temperature indication, and when the TRIP temperature is attained and then TRIP contacts are activated and motor supply is cut-off.