When the line voltage drops to 35%~70% of the rated voltage (within the conventional standard range, with slight differences in parameters from different manufacturers), the electromagnetic coil suction inside the release is insufficient, and the mechanical lock is released to drive the MCCB moving contact to quickly disconnect and cut off the main circuit. When the voltage completely disappears (voltage loss, power outage), the tripping and opening will also be triggered immediately; After the voltage returns to normal, the circuit breaker will not automatically close and needs to be manually reset and closed to eliminate the risk of automatic power transmission.

Inductive/electric equipment such as motors, compressors, and frequency converters may experience a decrease in speed and a sharp increase in current (locked rotor current) under undervoltage conditions. Prolonged operation can cause winding overheating, insulation aging, and even burnout. Timely power-off of undervoltage release devices can avoid such faults.

If there is no one on duty after a power outage, a sudden call can cause the equipment to start on its own, which may result in mechanical injury, equipment damage without load, chaotic production processes, fire and electrical safety accidents. Mandatory manual closing is a key safety design.

Under low pressure conditions, PLC, Precision equipment such as industrial control modules, instruments, servo systems, etc. may experience data confusion, control failure, and component breakdown. Early disconnection can avoid hardware damage and production failures.

When the voltage of the power grid fluctuates significantly and there is a local fault voltage drop, actively disconnect non critical loads to reduce the pressure of power grid recovery, prevent the expansion of the fault range, and ensure the priority of important circuit power supply.

The distribution cabinet is the core node of the power distribution system. The risks of equipment overload, short circuit, and spontaneous combustion caused by undervoltage will directly spread to the entire cabinet and even the workshop. The undervoltage release, as a front-end protection, can cut off the circuit in the early stage of voltage abnormality, reducing the probability of electric shock, fire, and mechanical accidents from the source.

The distribution cabinet is usually divided into main incoming circuit breakers and branch circuit breakers. Under voltage release devices with different action thresholds can be configured to achieve graded release: non essential auxiliary circuits are disconnected first, while key circuits such as main equipment, fire protection, and emergency lighting are retained for power supply. To avoid under voltage in a single circuit causing the entire cabinet and distribution room to trip, reduce the scope of power outages, and improve power supply continuity.

Continuous production lines, chemical plants, cold chain systems, medical equipment, etc. are not allowed to start or stop in disorder. Undervoltage tripping can prevent equipment from operating under pathological voltage conditions, avoiding product scrap, process interruption, and medical accidents. For linked equipment such as water pumps, fans, and air compressors, it can prevent multiple devices from running under pressure at the same time, causing abnormal pressure in the pipeline network, unit resonance, and system paralysis.

Linked with the voltage meter, intermediate relay, and sound and light alarm device of the distribution cabinet, an alarm is synchronously issued when the voltage is abnormal, prompting the operation and maintenance personnel to investigate the problems of the circuit, transformer, and higher-level power supply. The characteristic of mandatory manual closing requires operation and maintenance personnel to confirm voltage recovery and equipment failure before power transmission, standardize operating procedures, and reduce misoperation and power transmission with faults.

In special places such as high-rise buildings, mines, oil fields, hazardous chemical workshops, hospital operating rooms, etc., undervoltage protection of distribution cabinets is a mandatory safety requirement, used to prevent explosions, fires, and medical accidents caused by accidental power outages, in compliance with electrical safety regulations and industry standards.