Widely used in civil construction, national defense, mining, agriculture, transportation and other industries, it plays a big role in the distribution and transmission of electric power, circuit protection and control, and is a product with large usage and wide coverage.

As users do not have a deep or comprehensive understanding of the technology and characteristics of molded case circuit breakers, some concepts are particularly confusing and prone to misunderstandings and deviations in practical applications. 

This article introduces the problems that users are prone to in the use and selection of molded case circuit breakers, which helps users to choose molded case circuit breakers reasonably.

The rated current of the housing frame of the molded case circuit breaker is the rated current of the maximum tripping device that can be installed on the frame and the molded case of the same basic dimensions.

The rated current of the molded case circuit breaker is the current through which the circuit breaker striker can pass for a long time, also known as the rated current of the circuit breaker striker.

The same series of molded case circuit breakers have multiple rack level rated currents, and the same rack level rated currents have multiple rated currents. For example, the DZ20 series has 100, 225, 400, 630, 800, 1250 and other frame level rated currents. 100 frame level rated currents are 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100 225A frame level rated currents are 100A, 125A, 160A, 180A, 200A, 225 A rated current. DZ20-100 and DZ20-225 two frame grade have 100A rated current, but the volume, shape and breaking capacity of the circuit breaker is different, please fill in the model number completely, that is, the specific frame grade rated current within the rated current of the circuit breaker for selection. Rated current rating is selected by (1.25 ) priority factor. On the other hand, it is necessary to meet and satisfy the maximum line and electrical component rated current. On the other hand, standardization is carried out to obtain the best use and processing of the wire. Therefore, the levels of 3(6), 8, 10, 12.5, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400A, etc. are specified According to this regulation, when the calculated load of the line is 90A, only 100A specifications can be selected, so it will affect the protection performance to some extent.

The decoupler current rectification value is the decoupler adjusted to the action current value. This is a multiple of the rated current In, which is the action current value. For example, if the overcurrent is adjusted to 1.2, 1.3, 5, 10 times the current, then write Ir = 1.2In, 1.3In, 5In, 10In, etc. At present, some electronic decoupler overload length delayed rated current adjustable, the regulated current is actually rated current, is the maximum current that can be passed for a long time.

Rated action current is the actual action current of the contact under a certain action voltage when the auxiliary contact (accessory) is installed, the current is 3A or 6A, which is used for control and protection of the circuit.

Insulation rated voltage is the voltage value of the design circuit breaker, the electrical clearance and leakage distance is determined with reference to this value. Some circuit breakers do not specify the rated insulation voltage, the maximum of the rated operating voltage should be considered as the rated insulation voltage, the maximum rated operating voltage in any case does not exceed the rated insulation voltage. 

Rated operating voltage refers to the voltage value associated with the switching capacity and use category, the rated operating voltage of the molded case circuit breaker is mostly 50Hz, 380V, but there are also 50Hz, 600V, rated operating voltage 380V, 50Hz molded case circuit breaker, respectively 660V and 1140V

Rated short-circuit breaking capacity refers to the breaking capacity under the specified conditions. After acting according to the specified test procedure, the circuit breaker is not considered to continue carrying its rated current.

Rated operating, short-circuit breaking capacity is the breaking capacity under the specified conditions. After following the prescribed test procedure, the circuit breaker should be considered to continue carrying its rated current.

The rated control power supply voltage is the voltage at which the branch decoupling device and motorized mechanism accessories are installed on the molded case circuit breaker. There are two voltages, AC and DC, which must be specified when selecting AC or DC.

In addition, in order to meet the needs of different users, many domestic circuit breaker manufacturers of the same rack level of rated current short-circuit breaking capacity is divided into different levels, such as Changshu Switchgear Factory CM1-100 for C basic type (25 ~ 35kA ), L h high division circuit break type) 85 ~ 100kA ) of the user to meet the circuit breaker limit short-circuit breaking capacity, so that the line expected short-circuit current to meet the requirements, even if not artificially added insurance factor, will not cause waste.