LED Indication

Local Indicator

The LEDs and their meaning depend on the type of MicroLogic trip unit.

Type of MicroLogic trip unit	Description
Distribution	Ready LED (green) blinks slowly when the standard protection functions of the electronic trip unit are operational. Overload pre-alarm LED (orange) lights when the load exceeds 90% of the Ir setting. Overload alarm LED (red) lights when the load exceeds 105% of the Ir setting.
Motor	Ready LED (green) blinks slowly when the standard protection functions of the electronic trip unit are operational. Overload temperature alarm LED (red) lights when the motor thermal image exceeds 95% of the Ir setting.

Operation of the Ready LED

The Ready LED (green) blinks slowly when the standard protection functions of the electronic trip unit are operational. It indicates that the trip unit is operating correctly.

For MicroLogic 5 and 6 trip units: the Ready LED blinks at a value equal to the sum of the circuit breaker current for each phase and the neutral above a limit value. This limit value is indicated above the Ready LED, on the front face of the MicroLogic trip unit.

The following table uses two examples to illustrate the comparison of the phase and neutral currents with the activation limit value of the Ready LED:

MicroLogic 5.2 trip unit, 40 A rating, 3-pole	MicroLogic 5.3 trip unit, 400 A rating, 4-pole
The limit value is 15 A.	The limit value is 50 A.
This limit value can be: The sum of the 5 A phase current intensities (three balanced phases). 7.5 A in each of two phases (the current intensity in the third phase is zero). 15 A in one phase if the circuit breaker (3-pole): is installed on a distribution with distributed neutral. only has one loaded phase on a single-phase load. The current in the other two phases is zero.	This limit value can be: The sum of the three 15 A phase current intensities and a 5 A neutral current intensity. 25 A in each of two phases (the current intensity in the third phase and in the neutral is zero). 25 A in one phase and in the neutral (the current intensity in the other two phases is zero).

MicroLogic 5.2 trip unit, 40 A rating, 3-pole

MicroLogic 5.3 trip unit, 400 A rating, 4-pole

The limit value is 15 A.

The limit value is 50 A.

This limit value can be:

The sum of the 5 A phase current intensities (three balanced phases).
7.5 A in each of two phases (the current intensity in the third phase is zero).
15 A in one phase if the circuit breaker (3-pole):
- is installed on a distribution with distributed neutral.
- only has one loaded phase on a single-phase load.
The current in the other two phases is zero.

This limit value can be:

The sum of the three 15 A phase current intensities and a 5 A neutral current intensity.
25 A in each of two phases (the current intensity in the third phase and in the neutral is zero).
25 A in one phase and in the neutral (the current intensity in the other two phases is zero).

The MicroLogic 7 trip unit with integrated earth-leakage protection has an internal voltage power supply (in addition to the supply provided by the current transformers) to power the earth-leakage protection even when the current demand is low. The Ready LED blinks irrespective of the load, indicating that the standard protection functions are operational.

Operation of Pre-Alarm and Alarm LEDs (Electrical Distribution Protection)

The pre-alarm (orange LED) and alarm (red LED) indications trip as soon as the value of one of the phase currents exceeds 90% and 105% respectively of the Ir pickup setting:

Pre-alarm

Exceeding the pre-alarm threshold at 90% of Ir has no effect on the long-time protection.
Alarm

Crossing the alarm threshold at 105% of Ir activates the long-time protection with a trip time delay that depends on:
- The value of the current in the load
- The setting of the time delay tr

NOTE: If the pre-alarm and alarm LEDs keep lighting up, carry out load shedding to avoid tripping due to a circuit breaker overload.

The following figure illustrates the information supplied by the LEDs:

1 Current in the load (most heavily loaded phase)

2 Thermal image calculated by the trip unit

Operation of Alarm LEDs (Motor Protection)

The alarm indication (red LED) trips as soon as the value of the motor thermal image exceeds 95% of the Ir pickup setting.

Crossing the threshold of 95% of Ir is a temperature alarm: long-time protection is not activated.

The following figure illustrates the information supplied by the LED:

1 Current in the load

2 Thermal image calculated by the trip unit