Systems & Electronics

IMT4L – Digital multifunction motor protection relay

The multifunction protection relay IMT4L belongs to SIGMAL digital protection line and it performs functions as multifunction motor protection relay. The user can select one or more of the functions listed in the table below:


Thermal overload 49
Three-phase overcurrent 50 51
Earth-fault overcurrent

50N 51N

Unbalanced load / loss of phase 46
Locked rotor / excessive start-up time 51R
Maximum number of startings 66
Undercurrent / loss of load 37
Breaker failure 50BF
Trip circuit supervisor


It is possible to select three-phase or two-phase connection. All the functions of the relay are fully programmable by front panel keyboard or through a RS485 serial interface using a personal computer with set-up program; furthermore the relay can be programmed through a remote control and monitoring system.

Thresholds – IMT4L manages the following thresholds:

  • 3 thermal overload thresholds
  • 2 three phase overcurrent thresholds
  • 2 earth fault overcurrent thresholds
  • 2 unbalanced load / loss of phase thresholds
  • 1 locked rotor / excessive start-up time threshold
  • 1 number of starts limitation threshold
  • 1 undercurrent or loss of load threshold

The first threshold of phase overcurrent, earth-fault and unbalanced load (l>, lo> and I2>) can be programmed either definite time or time dependent in compliance with IEC 60255-151 specifications. The thermal overload thresholds (ANSI 49) are time dependent. The other

thresholds are definite time only.

Definite time threshold delay can be combined with an additional delay controlled by the digital inputs.

The trip of a threshold is shown by LEDs and with a specific message on the display.