Protection Offered:

• LI (Long-Time and Instantaneous): This type of trip unit offers two types of protection—long-time delay and instantaneous protection. The long-time delay protection is usually adjustable and protects against overloads that can cause the temperature of the protected circuit to rise slowly over time. The instantaneous protection is designed to protect against very high overcurrents by tripping the circuit breaker immediately without any intentional delay.

• LSI (Long-Time, Short-Time, and Instantaneous): This type of trip unit includes an additional short-time delay protection compared to the LI type. The short-time delay allows for a brief period before tripping when a short circuit occurs, which can be useful in allowing transient currents to pass without tripping the circuit breaker (for example, the inrush current when motors start).

Application:

• LI Types: These may be used in applications where only overload and immediate short circuit protection are required without the need for differentiation between short and long duration faults.

• LSI Types: These are suitable for more complex applications that require discrimination between transient overcurrents and actual faults, thereby avoiding unnecessary trips and allowing for better coordination between protective devices in a power distribution system.