What is Modular Case Circuit Breaker?

Molded case circuit breakers can automatically cut off the current when the current exceeds the trip setting. Plastic case refers to the use of plastic insulators as the outer casing of the device to isolate the conductors and the grounded metal parts. Molded case circuit breakers usually contain thermal and magnetic trip units, while large models of molded case circuit breakers are equipped with solid state trip sensors. The trip unit is divided into: thermal magnetic trip and electronic trip. Commonly used rated currents are as follows: 16, 25, 30, 40, 50, 63, 80, 100, 125, 160, 200, 225, 250, 315, 350, 400, 500, 630A.

Working conditions of MCCB

Ambient air temperature:

○ The upper limit of ambient air temperature +40℃;

○ The lower limit of ambient air temperature is -5℃;

○ The average value of the ambient air temperature for 24 hours does not exceed +35°C.

● Altitude: The altitude of the installation site does not exceed 2000m.

● Atmospheric conditions:

The relative humidity of the atmosphere does not exceed 50% when the ambient air temperature is +40℃; it can have a higher relative humidity at a lower temperature; the monthly average maximum relative humidity of the wettest month is 90%, and the monthly average of the month is the lowest The temperature is +25℃, taking into account the condensation on the surface of the product due to temperature changes.

● Pollution degree: The pollution degree is level 3.

The main parameters

⑴Rated voltage

The rated voltage on the nameplate of the circuit breaker refers to the rated voltage of the main contact of the circuit breaker, and is the voltage value that guarantees the long-term normal operation of the contactor of the contactor.

(2) Rated current

The rated current on the nameplate of the contactor refers to the rated current of the main contact of the router, and is the current value that guarantees the long-term normal operation of the contactor of the contactor.

⑶ Tripping current

The tripping current is the current setting value that causes the overcurrent release to operate. When the circuit is short-circuited or the load is seriously overloaded, and the load current is greater than the tripping current, the main contact of the circuit breaker is broken.

⑷Overload protection current and time curve

The overload protection current and time curve are inverse time characteristic curves. The larger the overload current, the shorter the time for the thermal release to act.

⑸ Rated voltage of the undervoltage release coil

The rated voltage of the undervoltage release coil must be equal to the rated voltage of the line.

⑹The rated voltage of the shunt release coil

The rated voltage of the shunt release coil must be equal to the control power supply voltage.

⑺Rated ultimate short-circuit breaking capacity Icu

There are two types of breaking capacity indicators for circuit breakers: rated ultimate short-circuit breaking capacity Icu and rated operating short-circuit breaking capacity Ics.

The rated ultimate short-circuit breaking capacity Icu is the limit parameter of the breaking capacity of the circuit breaker. After several short-circuit faults are broken, the breaking capacity of the circuit breaker will decrease.

The rated operating short-circuit breaking capacity Ics is a breaking index of the circuit breaker, that is, the normal operation of the circuit breaker can be guaranteed after several short-circuit faults have been broken.

For molded case circuit breakers, as long as the Ics is greater than 25% Icu, it is considered qualified. Most of the circuit breakers on the market have Ics between (50%-75%) Icu.

⑻Current limiting and breaking capacity

Current-limiting and breaking capacity refers to the ability to limit the fault current when the circuit breaker trips when the circuit is short-circuited. When the circuit is short-circuited, the contacts of the circuit breaker open rapidly and an arc is generated, which is equivalent to inserting a rapidly increasing arc resistance in the line, which limits the increase of fault current and reduces the electromagnetic, electrical and thermal effects of the short-circuit current. Adverse effects on circuit breakers and electrical equipment, prolong the service life of circuit breakers. The shorter the breaker opening time, the better the current limiting effect, and the closer Ics is to Icu.

⑼ Tripping characteristics of miniature circuit breakers

The tripping characteristics of circuit breakers are divided into A, B, C, D, K, etc., and their respective meanings are as follows:

Type A tripping characteristics: The tripping current is (2～3) In, which is suitable for protecting semiconductor electronic circuits, measuring circuits with low-power power transformers, or systems with long circuits and small short-circuit currents;

Type B tripping characteristics: tripping current is (3～5) In, suitable for household power distribution system, protection of household appliances and personal safety protection;

Type C tripping characteristics: the tripping current is (5～10) In, which is suitable for protecting power distribution lines and lighting circuits and motor circuits with higher on-current;

D-type tripping characteristics: the tripping current is (10-20) In, which is suitable for protecting equipment with high inrush current, such as transformers, solenoid valves, etc.;

K-type tripping characteristics: With 1.2 times the thermal tripping operating current and 8-14 times the magnetic tripping operating range, it is suitable for protecting motor circuit equipment and has a high impact current resistance