Main parameters of molded case circuit breakers

(1) Rated Voltage: The rated voltage on the circuit breaker nameplate refers to the rated voltage of the main contacts of the circuit breaker, which is the voltage value that ensures the long-term normal operation of the contactor contacts.

(2) Rated Current: The rated current on the contactor nameplate refers to the rated current of the main contacts of the circuit breaker, which is the current value that ensures the long-term normal operation of the contactor contacts.

(3) Tripping Current: The tripping current is the current setting value that causes the overcurrent trip unit to operate. When the circuit is short-circuited or the load is severely overloaded, and the load current is greater than the tripping current, the main contacts of the circuit breaker will disconnect.

(4) Overload Protection Current-Time Curve: The overload protection current-time curve is an inverse time characteristic curve. The larger the overload current, the shorter the operating time of the thermal trip unit.

(5) Rated Voltage of Undervoltage Trip Unit Coil: The rated voltage of the undervoltage trip unit coil must be equal to the rated voltage of the line.

(6) Rated Voltage of Shunt Trip Unit Coil: The rated voltage of the shunt trip unit coil must be equal to the control power supply voltage.

(7) Rated Ultimate Short-Circuit Breaking Capacity Icu
There are two indicators for the breaking capacity of a circuit breaker: rated ultimate short-circuit breaking capacity Icu and rated operational short-circuit breaking capacity Ics.

Rated ultimate short-circuit breaking capacity Icu is the limiting parameter of the circuit breaker's breaking capacity. After breaking several short-circuit faults, the circuit breaker's breaking capacity will decrease.

Rated operational short-circuit breaking capacity Ics is a breaking indicator of the circuit breaker, meaning that after breaking several short-circuit faults, it can still guarantee normal operation.

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

(8) Current-Limiting Breaking Capacity
Current-limiting breaking capacity refers to the circuit breaker's ability to limit the fault current when a short circuit occurs. When a short circuit occurs, the circuit breaker contacts open rapidly, generating an electric arc. This is equivalent to introducing a rapidly increasing arc resistance in series with the circuit, thereby limiting the increase in fault current. This reduces the adverse effects of the electromagnetic, electrodynamic, and thermal effects of the short-circuit current on the circuit breaker and electrical equipment, extending the circuit breaker's service life. The shorter the circuit breaker's breaking 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 several types, such as A, B, C, D, and K, and their respective meanings are as follows: A-type tripping characteristics: the tripping current is (2~3)In, which is suitable for protecting semiconductor electronic circuits, measuring circuits with small power transformers, or systems with long circuits and small short-circuit currents; B-type tripping characteristics: the tripping current is (3~5)In, which is suitable for residential power distribution systems, protection of household appliances and personal safety protection; C-type tripping characteristics: the tripping current is (5~10)In, which is suitable for protecting power distribution lines and lighting circuits and motor circuits with high connection 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 and solenoid valves; K-type tripping characteristics: it has 1.2 times the thermal tripping current and 8~14 times the magnetic tripping range, which is suitable for protecting motor circuit equipment and has high resistance to inrush current [3].