Internal Accessories
Auxiliary Contacts: Contacts mechanically linked to the opening and closing mechanism of the circuit breaker's main circuit. They are primarily used to indicate the circuit breaker's open/closed status and are connected to the circuit breaker's control circuit. Through the opening and closing of the circuit breaker, they control or interlock related electrical components. For example, they output signals to indicator lights, relays, etc. Molded case circuit breakers with a frame rating of 100A use single-break changeover contacts; those with a frame rating of 225A and above use a bridge contact structure, with a specified thermal current of 3A. Those with a frame rating of 400A and above can be equipped with two normally open and two normally closed contacts, with a specified thermal current of 6A. The number of operating cycles is the same as the total number of operating cycles of the circuit breaker.
Alarm Contact: Used for alarming circuit breaker faults. This contact only operates after the circuit breaker has tripped. It is mainly used when the circuit breaker trips freely due to overload, short circuit, or undervoltage faults. The alarm contact changes from its normally open position to the closed position, activating indicator lights, bells, buzzers, etc., in the auxiliary circuit to display or remind the user of the circuit breaker's fault tripping status. Since the probability of a circuit breaker tripping freely due to a load fault is relatively low, the lifespan of the alarm contact is about 1/10 of the circuit breaker's lifespan. The operating current of the alarm contact generally does not exceed 1A.
Shunt Trip Unit: A shunt trip unit is a voltage-driven trip unit whose voltage is independent of the main circuit voltage. It is an accessory for remotely controlling the tripping operation. It can reliably trip the circuit breaker when the power supply voltage is equal to any voltage between 70% and 110% of the rated control power supply voltage. The shunt trip unit operates on a short-time duty cycle; the coil energization time generally cannot exceed 1 second, otherwise the wire will burn out. To prevent coil burnout, a microswitch is connected in series with the shunt trip coil of a molded case circuit breaker. When the shunt trip unit is attracted by its armature, the microswitch changes from a normally closed state to a normally open state. Since the control circuit for the shunt trip unit's power supply is disconnected, even if the button is manually pressed, the shunt trip coil will never be energized again, thus preventing coil burnout. When the circuit breaker recloses, the microswitch returns to the normally closed position.
Undervoltage trip unit: An undervoltage trip unit is a trip unit that causes the circuit breaker to disconnect with or without a delay when its terminal voltage drops to a specified range. When the power supply voltage drops (even slowly) to within 35% of the rated operating voltage, the undervoltage trip unit should operate. When the power supply voltage is equal to 35% of the trip unit's rated operating voltage, the undervoltage trip unit should be able to prevent the circuit breaker from closing; when the power supply voltage is equal to or greater than 85% of the undervoltage trip unit's rated operating voltage, under hot conditions, it should be able to ensure reliable circuit breaker closure. Therefore, when a certain voltage drop occurs in the power supply voltage of the protected circuit, the circuit breaker can automatically trip to disconnect the power supply, protecting the load appliances or electrical equipment downstream of the circuit breaker from undervoltage damage. In use, the undervoltage release coil is connected to the power supply side of the circuit breaker. The circuit breaker can only close after the undervoltage release is energized.
External Accessories
Electric Operating Mechanism: This is an accessory used for remote automatic opening and closing of circuit breakers. There are two types of electric operating mechanisms: motor-operated and electromagnet-operated. Motor-operated mechanisms are for molded case circuit breakers with a frame rating of 400A and above. Electromagnet-operated mechanisms are suitable for molded case circuit breakers with a frame rating of 225A and below. Whether using an electromagnet or a motor, their engagement and rotation directions are the same. Opening and closing are achieved solely by the position of the cam inside the electric operating mechanism. When the circuit breaker is operated by the electric mechanism, it should be able to reliably close at any voltage between 85% and 110% of the rated control voltage.
Rotary Operating Handle: Suitable for molded case circuit breakers. A rotary operating handle mechanism is installed on the circuit breaker cover. The handle's shaft is fitted into a mating hole in the mechanism, and the other end of the shaft passes through the drawer door opening. The handle is mounted on the exposed shaft end on the door of the assembly. The round or square base of the handle is screwed to the door. This installation allows the operator to close or open the circuit breaker by rotating the handle clockwise or counterclockwise from outside the door. Simultaneously, rotating the handle ensures that the cabinet door cannot be opened when the circuit breaker is closed; the switch panel door can only be opened when the handle is open or re-engaged. In an emergency, if the circuit breaker is "closed" and the door needs to be opened, the red release button next to the rotary handle base can be pressed.
Extended Handle: An external extended handle, directly mounted on the circuit breaker's handle. Generally used on high-capacity circuit breakers of 600A and above for manual closing and opening operations.
Handle locking device: A latch is installed on the handle frame, and a hole is drilled in the handle to lock it with a padlock. It is mainly used when the circuit breaker is closed.
When in operation, it prevents others from opening the circuit breaker and causing a power outage, or when the circuit on the load side of the circuit breaker needs maintenance or cannot be energized, to prevent accidental closing of the circuit breaker.