RACO International, L.P. a true pioneer of electric actuators were kind enough to share with us a case study they created for our Power Monitoring Relay,  G2BM400V12AL10. We are excited to share their work and how in detail our Power Monitor works with their actuator motor. The thrust level that the electro-mechanical actuator is developing, has a direct relationship with the electrical power consumption of the actuator motor. By monitoring and comparing the power consumption to a preset threshold value, a precise maximum thrust value can be defined.


The actuator motor true power monitoring relay (PMR 480V) operates in the fail safe mode for single and three phase power systems. When the actuator motor power is initially applied, a time delay begins to suppress the power spike due to the additional acceleration and inertia power requirements. The delay time is factory set and slightly longer than the inrush time.
Coal Unloading Facility

After the delay time has expired, the relay de-energizes when the actuator motor power rises above the preset trip point (this represents an over-thrust condition). The PMR 480V unit remains locked-out, if terminal Y1 and Y2 is connected, with the dry relay contacts open until the control voltage is interrupted and re-applied. An external CT may be used to extend the power range of the PMR 480V unit

Operational Function Minimum & Maximum Monitoring

The PMR 480V power monitoring unit is equipped with multiple functions for a wide range of power monitoring capabilities. The function which is utilized for the thrust overload protection of your actuator is the “Over O+I< Function” selected via the bottom rotary switch on the unit.

The next rotary switch up “Range” matches the connected motor power consumption at the rated actuator thrust value with the unit  measurement range. Four settings are available: 0.75, 1.5, 3, 6 kW.

The next rotary potentiometer “Delay” determines the time after which the unit should shut off after the thrust limit is reached. This time should be as short as possible to protect the actuator and the attached equipment from thrust overloading. The value is typically factory selected for 0.1 seconds. The potentiometer “Power” is used to adjust the thrust shut off point of the actuator. At the nominal rated thrust value of the actuator, the actuator motor will draw a precise electrical supply power value. The motor power consumption value will be calculated as a percentage of the selected power range (second rotary switch from the bottom).

Example: RACO Actuator T1A5 with a nominal thrust rating of 1100 lbf and a rated speed of 4.2”/sec. Supply Voltage: 480VAC, 3 Phase At rated thrust of 1100 lbf the motor will draw 1,831 W electrical power. Selected power range setting at the PMR 480V unit is 3kW. P1 should be set at:
1831 * 100  P1 = ——————- % = 61.0 % 3000 To block out the power consumption readings during start-up in retract or extend direction, a start-up delay time can  be selected. The potentiometer start is typically factory set at 1 sec. In rare cases where huge masses are connected to the
actuator which need to be accelerated or decelerated, a slightly higher start-up time  may be required. Settings above 2 to 3 sec indicate dynamic overloading of the actuator. Please consult factory. The below diagram illustrates the behavior of the thrust overload protection unit PMR

Terminal Layout

Looking at the front plate, the A1 terminal is located on the left site of the bottom terminal strip. The L1 terminal is located on the left site of the upper terminal strip.