MicroLogic Trip Unit Functions

Long-Time Trip Functions

The long-time pickup switch sets the maximum current level the circuit breaker will carry continuously. The maximum current level (I_r) is the long-time pickup setting multiplied by the sensor plug amperage (I_n). If the current exceeds this value for longer than the long-time delay time, the circuit breaker will trip.

The long-time delay switch sets the length of time that the circuit breaker will carry a sustained overload before tripping. Delay bands are labeled in seconds of overcurrent at six times the ampere rating. For maximum coordination, there are eight delay bands. Long-time delay is an “inverse time” characteristic in that the delay time decreases as the current increases.

The trip unit includes an alarm indicator that will be lit continuously when the current is above 100% of the pickup setting.

Short-Time and Instantaneous Trip Functions

The short-time pickup switch sets the short-circuit current level at which the circuit breaker will trip after the set short-time delay. The short-time current (I_sd) equals the short-time pickup setting multiplied by the long-time pickup (I_r).

The short-time delay switch sets the length of time the circuit breaker will carry a short circuit within the short-time pickup range. The delay (based on 10 times the ampere rating I_r) can be adjusted to four positions of I²t ramp operation (I²t ON) or five positions of fixed time delays (I²t OFF). I²t ON delay is an “inverse time” characteristic in that the delay time decreases as the current increases. Short-time delay for the 2.0 trip unit is fixed at a delay band of 20 to 80 ms

The instantaneous pickup switch sets the short-circuit current level at which the circuit breaker will trip with no intentional time delay. The instantaneous current (I_i) is equal to the instantaneous pickup setting multiplied by the sensor plug amperage (I_n).

The instantaneous function will override the short-time function if the instantaneous pickup is adjusted at the same or lower setting than the short-time pickup. In trip units with both adjustable short-time and instantaneous trip functions, the adjustable instantaneous trip can be disabled by setting Instantaneous pickup to OFF.

Ground-Fault Trip Functions

The ground-fault pickup switch sets the current level at which the circuit breaker will trip after the set ground-fault delay. Ground-fault pickup values (I_g) are based on circuit breaker sensor plug (I_n) only, not on the rating plug multiplier (I_r). Changing the rating plug multiplier has no effect on ground-fault pickup values.

The ground-fault delay switch sets the length of time the circuit breaker will carry ground-fault current which exceeds the ground-fault pickup level before tripping. The delay (based on the sensor plug amperage (I_n) can be adjusted to four positions of I²t ramp operation (I²t ON) or five positions of fixed time delays (I²t OFF). I²t ON delay is an “inverse time” characteristic in that the delay time decreases as the current increases.