601 Series - 3-Phase Voltage & Frequency Monitor

Littelfuse Voltage Monitoring Relays
The Model 601 is a fully-programmable voltage monitor designed to protect 3-phase motors. It can be used as a stand-alone product or networked with an RM-1000, RM-2000, PLC, computer or SCADA system.


When a harmful condition is detected, the 601’s output relay is deactivated after the specified trip delay. The output relay reactivates after power line conditions return to an acceptable level for the programmed restart delay (RD2).


Eleven (11) setpoints are viewable with the 3-digit LED display or from a networked device:

    low voltage
      high voltage
        voltage unbalance
          low frequency
            high frequency
              RS485 address
                trip delay for voltage/frequency faults
                  trip delay for single-phase faults
                    rapid-cycle timer (RD1)
                      restart delay after all faults (RD2)
                        type of restart after all faults (manual or automatic)

                        Six (6) parameters are viewable while the motor is running:

                          L1-L2 voltage
                            L2-L3 voltage
                              L1-L3 voltage
                                average voltage
                                  voltage unbalance (%)
                                    voltage frequency (%)


                                    When used with the RS485MS-2W communications module, the 601 can communicate with most Modbus RTU master devices. Voltage conditions can be monitored and setpoints can be changed remotely using Solutions software, an RM-1000, RM-2000 or other device.

Access specifications, certifications, check availability and order parts below

Catalog #Input
Voltage (V)
Termination TypeMounting MethodDimensionsWeight (lbs/g)Compare
601200 to 480VACTorque: 7in-lbsSurface mount (4 - #8 screws) or DIN rail mount3.05 in H x 3.85 in W x 5.05 in D (77.5 x 97.8 x 128.3 mm)1.2 lbs. (19.2 oz. 544.3 g)
601575500 to 600VACTorque: 7in-lbsSurface mount (4 - #8 screws) or DIN rail mount3.05 in H x 3.85 in W x 5.05 in D (77.5 x 97.8 x 128.3 mm)1.2 lbs. (19.2 oz. 544.3 g)