Trip Units
1. Circuit breaker trip system shall be ABB series electronic trip units.
2. The trip unit should consist of a solid-state trip actuator and current sensors. Rating plugs
to be sized as needed to meet the drawings without the need to remove and change CTs.
3. The trip units shall incorporate “True RMS sensing”.
4. The trip unit should not require an external power supply for protection. Power should be
supplied through CTs integral to the circuit breaker.
5. The trip unit protective functions shall not rely on or operate from internal batteries.
6. The minimum basic trip unit functions and settings should include:
a. PR121 Series Trip Unit
1). Overload Protection (L): Characteristic t = k/I2
trip threshold settings ranging
from I = (0.4 - 1) X In of the rated value and timing adjustable between
3 – 18 seconds.
2). Short Time protection with adjustable delay (S): Characteristic t = k and
t = k/I2
trip threshold settings ranging from I = (1 - 10) X In of the rated value
and timing adjustable between 0.05 – 0.4 seconds.
3). Instantaneous Short Circuit Protection (I): Trip threshold I = (1, 5,….12) X In
of rated CT value.
4). Ground Fault Protection (G): Characteristic t = k/I2
trip threshold settings
ranging from I = (0.2 - 0.48) X In of the rated value and timing adjustable
between 0.1 – 0.4 seconds.
5). All protective functions except Overload (L) must be capable of being
disabled while maintaining UL approval.
6). Trip unit settings should be accomplished by means of dip switches on the
front of the trip unit.
7). The trip unit should include alarm LED signal for the “L” and “S” function.