Many motors, transformers and generators are fitted with positive
temperature co-efficient thermistor temperature sensors. The addition
of a thermistor trip relay will provide full protection against sustained
overload, single phasing, locked rotor, blocked ventilation and high
ambient temperature. Thermistor trip relays continuously monitor the
working temperature inside electrical equipment. When the temperature
exceeds a safe limit, the relay can be used to shut down equipment until
it regains a safe operating temperature.
Operation
Thermistors are simple low cost temperature sensors. The thermistor trip protector
operates by de-energising a relay when the thermistors detect a critical temperature
condition. An illuminated green LED indicates when the temperature is within normal
working limits. Any number of thermistors may be used in series connection providing
the resistance at normal working temperature is less than 1500 ohms.
There are no user adjustments on this relay.
Model 252-PMT will automatically reset when temperature returns to normal.
For model 252-PMM, fitting a link between terminals R1 and R2 will latch the product
in its tripped state when an over-temperature condition is detected. The relay can be
reset by pressing the front panel reset switch, opening the R1–R2 link, or interrupting
the auxiliary supply. |
