400a 3p Mccb Enclosed Molded Case Switch

A 400a 3p mccb enclosed molded case switch is a type of breaker with a molded insulating enclosure and air insulation. It is commonly installed and applied in low voltage distribution systems to interrupt or isolate both normal currents and fault currents within the rated range, which helps to protect cables and electrical equipment. Common tripping methods for A 400a 3p mccb enclosed molded case switch include magnetic only, thermal magnetic, and electronic trip units.

A magnetic only trip operates solely under short circuit conditions. In other words, the 400a 3p mccb enclosed molded case switch trips only when a fault such as a short circuit occurs. This type is often used in heater circuits or in motor circuits where separate overload protection is already provided.

Thermal magnetic trip units respond to both short circuits and sustained over current. If the current exceeds 400A for a certain period or a short circuit occurs, the 400a 3p mccb enclosed molded case switch will trip. Because it combines two protection mechanisms, it is sometimes referred to as a combined or dual trip on a 400a 3p mccb enclosed molded case switch, which is commonly applied in general power distribution.

Electronic trip units represent a more advanced and mature solution. With this type, parameters such as magnetic pickup, thermal settings, and tripping delay can be adjusted, making the 400a 3p mccb enclosed molded case switch suitable for a wider range of applications. However, this added flexibility usually comes with a higher cost.

In addition to these types, there are molded case circuit breakers specifically designed for motor protection. For such applications, the magnetic trip setting is typically higher, which is more than ten times the rated current, so that the molded case circuit breaker can withstand the high inrush current during motor startup without tripping unnecessarily, while still providing protection under fault conditions.  

400a 3p mccb enclosed molded case switch parameter:

Functions of 400a 3p mccb enclosed molded case switch Accessories

Accessories extend and complement the basic functions of a 400a 3p mccb enclosed molded case switch. They add control options and enhance protection features to make them an integral part of the device. Common accessories of a 400a 3p mccb enclosed molded case switch include auxiliary contacts, alarm contacts, shunt trip units, under voltage releases, motor operators, and external rotary handles.

1) Auxiliary Contacts

Auxiliary contacts are mainly used to indicate whether the 400a 3p mccb enclosed molded case switch is open or closed, but they do not show if a fault trip has occurred. They are connected to the control circuit. For molded case circuit breakers, a frame size of 400A and above, configurations of two normally open and two normally closed contacts are available with a thermal current of around 6A. A frame size of 100A typically uses a single break changeover contact, while 225A and 250A and to adopt a bridge contact structure with a conventional thermal current of about 3A.

2) Alarm Contacts

Alarm contacts are designed to signal when the 400a 3p mccb enclosed molded case switch trips automatically due to faults such as overload, short circuit, or under voltage. Their operating current is generally AC 380V at 0.3A or DC 220V at 0.15A, but it usually does not exceed 1A. However, the thermal current typically falls within the range of 1 to 2.5A.

3) Shunt Trip Unit

A shunt trip unit allows the 400a 3p mccb enclosed molded case switch to be opened remotely. Its operating voltage can be independent of the main circuit voltage. It is intended for short time duty, and the coil energizing time should normally not exceed one second, otherwise the coil may be damaged.

To prevent coil burnout, a microswitch is connected in series with the shunt trip coil. When the coil is energized, the armature is attracted, which causes the microswitch to change from a normally closed to a normally open state. This interrupts the control circuit, so even if the push button is held down, the coil will not remain energized. This design effectively protects the coil from overheating. Once the 400a 3p mccb enclosed molded case switch is reset and closed again, the microswitch returns to its normally closed position. Shunt trip units are available in various control voltages and frequencies to suit different applications.

4) Under Voltage Release

The under voltage release is used to protect circuits and power equipment from low voltage conditions. Its coil is connected to the supply side of the molded case circuit breaker, and the breaker can only be closed when the coil is energized. If the voltage is too low, the 400a 3p mccb enclosed molded case switch cannot be closed. It is important to ensure that the system voltage matches the rated voltage of the under voltage release. The operating range is typically between 70% and 35% of the rated voltage. These devices are also available in different voltage ratings and frequencies for various applications.

5) Motor Operator Mechanism

Motor operators are used for automatic and remote closing and opening of circuit breakers. There are two main types, which are motor driven and electromagnetic. Motor driven mechanisms are generally used for molded case circuit breakers MCCBs with a frame size of 400A and above, while electromagnetic operators are more suitable for MCCBs rated 225A and below.