VCB in HT/MV Panels
A Vacuum Circuit Breaker (VCB) is commonly used in HT/MV panels because it is designed for medium-voltage systems and provides reliable arc interruption. When the contacts separate during a fault, the arc is extinguished inside a vacuum interrupter, providing fast interruption, good dielectric strength, high reliability, and low maintenance.
ACB in LT Panels
An Air Circuit Breaker (ACB) is widely used in LT panels for high-current, low-voltage applications such as incomers, bus couplers, and outgoing feeders. It uses air as the arc-extinguishing medium and, with its electronic trip unit, can provide overload, short-circuit, and earth-fault protection.
Important Difference
The main difference is the system voltage, current, fault level, and arc-interruption requirements. VCBs are generally preferred for HT/MV applications while ACBs are commonly selected for high-current LT distribution systems.
The selection of a VCB or ACB should not be based on voltage alone. Rated voltage, continuous current, short-circuit breaking capacity, protection requirements, insulation level, and system design must all be considered.