C-mac® module type RP81 is used to monitor the load of 3-phase motors, because the phase angle between the motor voltage and -current (cos phi) is changing dynamically with the mechanical load of the motor.
The biggest change occur, if the motor load is between 0 og 60%. Therefore the RP81 is suitable for monitoring wedges, dry running of pumps and so on.
RP81 can be connected directly to motors with a nominel motor current up to 6 A. If the motor current is bigger, a standard current transformer must be used in connection to the monitoring. The module ie equipped with an adjustable start-up delay, that ensures the relay stay activated regardless the load, when the motor starts.
It is also possible to select, if the relay of the module must drop off by over- or under load.