How to choose the type of MCCB, the meaning of the parameters of MCCB, and the method of wiring the MCCB

MCCB
MCCB

How to choose the type of MCCB(molded case circuit breaker), the meaning of the parameters of MCCB(molded case circuit breaker), and the method of wiring the MCCB(molded case circuit breaker)

 

Selection of MCCB(Molded Case Circuit Breakers)

1、Grade of circuit breaker shell

Circuit breaker housing rated current is the rated current of the maximum release that can be installed in the same basic frame and plastic housing. Circuit breaker rated current refers to the current that the trip unit in the circuit breaker can pass for a long time. It is also called the rated current of the circuit breaker trip unit.

There are several kinds of shell frame rated current in the same series, and there are multiple rated currents in the same shell frame rated current. For example, in the DZ20 series, there are 100, 225, 400, 630, 800, 1250 and other shell frame rated currents, while the rated currents in the 100 frame rated current are 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A rated Current; 225A shell rated current in 100A, 125A, 160A, 180A, 200A, 225A rated current. DZ20-100 and DZ20-225 have 100A rated current in two kinds of shell frame grades, but the circuit breaker volume shape and breaking capacity are not the same, so when the selection is completed, the model should be filled in, ie the specific circuit breaker within the rated level of the shell frame rated current. Rated current. The rated current rating is selected according to the (1.25) priority factor: on the one hand, it meets and meets the requirements for the maximum line and rated current of the electrical components; on the other hand, it is for standardization to achieve the best use of wire and the benefits of processing. Therefore, the levels it provides are: 3(6), 8, 10, 12.5, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400A and so on. Because of this provision, when the line calculation load is 90A, only the 100A specification can be selected, thus affecting its protection performance to some extent.

The release current setting means that the release adjusts to the operating current value. It refers to the multiple of the rated current In, which is the operating current value. For example: overcurrent is set to 1.2, 1.3, 5, and 10 times the current, and Ir=1.2 In, 1.3 In, 5 In, and 10 In are written. At present, some electronic trip units have an adjustable long-delay rated current. The adjusted current is still the rated current and is the maximum current that can be passed for a long time.

The rated operating current is the actual operating current of the contactor at a certain working voltage when the circuit breaker is installed with an auxiliary contact (accessory), and the current is 3A or 6A for controlling and protecting the circuit.

2.Rated insulation voltage

The rated insulation voltage is the voltage value of the designed circuit breaker. The clearance and creepage distance should be determined with reference to this value. Some circuit breakers do not specify the rated insulation voltage. The maximum value of the rated operating voltage shall be regarded as the rated insulation voltage. In any case, the maximum rated working voltage shall not exceed the rated insulation voltage, and the rated insulation voltage and the power frequency test voltage of the circuit breaker as follows.

The rated operating voltage refers to the switching capacity and the voltage value related to the use category. The rated operating voltage of MCCB(molded case circuit breakers) is mostly 50Hz and 380V, but there are also 50Hz and 600V MCCB(molded case circuit breakers) with rated operating voltages of 380V and 50Hz. Allow to use 660V or 1140V power supply voltage.

The rated control power supply voltage is the voltage when the MCCB(molded case circuit breaker) is equipped with the shunt release and the accessory of the motor-driven mechanism. There are AC and DC voltages, which must be specified when selecting AC or DC.

3.Rated limit short-circuit breaking capacity

The rated ultimate short-circuit breaking capacity refers to the breaking capacity under the specified conditions. After acting according to the specified test procedure, it is not considered that the circuit breaker continues to carry its rated current. Rated operating short-circuit breaking capacity refers to the breaking capacity under the specified conditions. After the prescribed test procedure, the circuit breaker shall be considered to continue to carry its rated current.

In order to meet the needs of different users, many circuit breaker manufacturers in China now classify the short-circuit breaking capacity of the rated current of the same frame into different levels. For example, Changshu Switching Plant CM1-100 is divided into C basic type (25-35kA), L standard. Type (35 ~ 50kA), M higher breaking type (50 ~ 75kA), H high breaking type (85 ~ 100kA). When the user selects, it must meet the limit short-circuit breaking capacity of the circuit breaker, and the expected short-circuit current of the line can meet the requirement, and it is not necessary to artificially add the coefficient of insurance so as to avoid waste.

Rated operating short-circuit breaking capacity can be 25%, 50%, 75%, 100% of rated limit short-circuit breaking capacity, most circuit breakers are 50% to 75%, extremely few are 100% (Ics=Icu), Such as France’s Schneider’s Merlin Gerin company’s NS products.

4.Attachment function

The accessory, as a derivative and supplement of the circuit breaker function, adds control means and expands the protection function for the circuit breaker. It is an integral part of the circuit breaker and mainly includes the auxiliary contact, the alarm contact, the shunt release, and the under voltage. Releases, electric operating mechanisms, external turning operating handles and other accessories.

Auxiliary contacts are mainly used to display the status of circuit breaker split and close but cannot display whether the fault trips, and are connected to the control circuit of the circuit breaker. The rated current of MCCB(molded case circuit breaker) shell frame 100 is a single breakpoint switching contact, 225 and The above is a bridge-type contact structure, and it is agreed that the heating current is 3A; the shell frame rated current of 400 or more can be installed with two normally open and two normally closed, and the convention heating current is 6A.

The alarm contacts are mainly used for tripping when the load of the circuit breaker is overloaded, short-circuited, or undervoltage. The operating current of the alarm contact is: AC380V, 0.3A, DC220V, 0.15A, generally does not exceed 1A, and the heating current can be in the range of 1 to 2.5A.

The shunt release is an accessory for long-distance operation and opening. Its voltage can be independent of the main circuit voltage. The shunt release is a short-time working system. The coil power-on time cannot exceed 1s in general, otherwise the coil will burn. MCCB(Molded Case Circuit Breaker) To prevent the coil burned out, a micro switch is connected in series with the shunt release coil. When the shunt release is energized, the armature pulls in and the micro switch is switched from normally closed to normally open due to shunt release. The control circuit of the power supply of the device is cut off. Even if the button is manually pressed, the split coil is no longer energized. The generation of burnout of the coil is avoided, and the microswitch is again in the normally closed position when the circuit breaker is re-engaged. Shunt trip units have a variety of control voltages and different power supply frequencies. They can be used in different applications and different power supplies.

The undervoltage release is used for long-term voltage protection of the line and power supply equipment. When used, the undervoltage release coil is connected to the power supply side of the circuit breaker. After the undervoltage release is energized, the circuit breaker can be closed, otherwise the circuit breaker cannot be closed. . The user should confirm whether the line is consistent with the operating voltage of the undervoltage release. The undervoltage operating range is (70% to 35%) Un. Undervoltage release also has a variety of rated operating voltages and different power supply frequencies. It can be used in different occasions and different power supplies.

Electric operating mechanisms are used for the automatic control of circuit breakers and for remote closing and opening. There are two kinds of electric operating mechanism and electromagnetic operating mechanism: the electric operating mechanism is driven by the motor, generally applicable to the circuit breaker with shell frame rated current 400A and above, and the electromagnet operating mechanism is applicable to the circuit breaker with shell frame rated current 225A and below.

5.Arc distance

When a circuit breaker breaks a large short-circuit current, an arc is generated when the movable and static contacts are separated. A part of the arc or ionized gas is ejected from the power supply terminal of the circuit breaker. The arc itself is a huge current, which easily leads to The phase-to-phase short circuit and grounding short-circuit accidents between the exposed electrical conductors and between the bare charged body and the ground (the metal housing of the equipment is grounded). To ensure safety, users should leave a certain distance according to the manufacturer’s product samples or the data provided in the user’s manual. If the height of the distribution box or cabinet is not enough, products with small arcing arc or arcing arc may be used to ensure the safety of electricity usage.

 

 Considerations of MCCB(Molded Case Circuit Breakers) Selection

1)Different breaking capacity

MCCB(Molded case circuit breaker) breaking capacity has two important indicators: rated operating short-circuit breaking capacity Ics (according to the conditions specified by the specified experimental procedures, including the ability of the circuit breaker to continue carrying its rated current capacity) and rated limit short-circuit breaking capacity Icu ( The conditions specified by the specified test procedure include the ability of the circuit breaker to continue to carry its rated current capacity. The difference between the two is that the rated limit short-circuit breaking capacity means that the circuit breaker can operate again after breaking the three-phase short-circuit current at the outlet end, and then break the short-circuit current once. As for whether the normal connection and breaking can be performed later, it is not guaranteed. . However, the rated short-circuit breaking capacity of the operation must be able to be normally broken several times under the above conditions.

2)Cooperative use between circuit breakers

The choice of a single circuit breaker directly affects the selection of the overall accessory circuit and conductor cross-section. The circuit breaker must be selected according to the overall composition of the system. In order to achieve faults at any point on the line, it is possible to eliminate the faults from the circuit breakers of neighboring upper levels.

 

 The meaning of several circuit breaker parameters

Frame current Iu: also known as rated uninterrupted current. Refers to the current value under the specified conditions when the temperature rise of each component under the long-term working system does not exceed the specified limit value.

Rated operating current Ie: refers to the current value under the specified conditions to ensure the normal operation of the electrical equipment. It is related to factors such as rated voltage, grid frequency, rated operating system, use category, contact life, and degree of protection. It is sometimes identified as In.

Rated current setting value Ir: This is a current value set by the user through the release of the circuit breaker. The circuit breaker is overloaded and short-circuit protected according to the user’s set Ir. For example, ABB’s MCCB S5N400R320PR112/LIFF3P, Iu = 400AIe = 320A, Ir = (0.4-1) Ie adjustable. Extreme short-circuit breaking capacity Icu circuit breaker must be able to reliably break short-circuit faults when subjected to this short-circuit current, but does not require the circuit breaker to continue to use without maintenance or replacement parts.

Rated operating short-circuit capability Ics: The circuit breaker must reliably break short-circuit faults when subjected to this short-circuit current, but it is required that the circuit breaker can continue to be used again without maintenance or replacement of parts. Ics must be less than or equal to Icu, which is generally expressed as Ics=xx%Icu.

Rated short-time withstand current Icw: The circuit breaker is required to withstand a certain short-circuit current in a certain period of time, is not damaged and can still perform its function reliably. The short-term withstand current must give two values, one for time and one for current. For example, 1S, 45KA means that the current can withstand 45K in 1S.

 

 

The meaning of numbers commonly used in the selection of MCCB(molded case circuit breakers)

2200 “2” represents 2-pole switch, “200” represents electromagnetic instantaneous trip
2300 “2” represents 2-pole switch, “300” represents thermal-electromagnetic
3200 “3” represents 3-pole switch, “200” represents electromagnetic instantaneous trip
3300 “3” represents 3-pole switch, “300” represents thermal-electromagnetic
3308 “3” represents 3-pole switch and “308” represents installed alarm switch
3310 “3” represents 3-pole switch and “310” represents additional shunt switch
3320 “3” represents 3-pole switch and “320” represents additional auxiliary switch
3330 “3” for 3-pole switch, “330” for under-voltage switch (additional)
3340 “3” represents 3-pole switch, “340” represents added auxiliary switch and shunt switch
3350 “3” represents 3-pole switch, “350” represents additional shunt switch and undervoltage switch
3360 “3” represents 3-pole switch, “360” represents the addition of two auxiliary switches
3370 “3” represents 3-pole switch, “370” represents auxiliary switch and undervoltage switch
3318 “3” represents 3-pole switch, “318” represents additional shunt switch and alarm switch
3328 “3” stands for 3-pole switch, “328” stands for auxiliary switch and alarm switch
3338 “3” represents 3-pole switch, “338” represents installation of under-voltage switch and alarm switch
3348 “3” represents 3-pole switch, “348” represents additional shunt switch and auxiliary switch and alarm switch
3368 “3” represents 3-pole switch, “368” represents adding 2 groups of auxiliary switch and alarm switch
3378 “3” represents 3-pole switch, “378” represents auxiliary switch and undervoltage switch and alarm switch

Wiring method of MCCB(Molded Case Circuit Breakers)

1.The pre-board connection mode is the default connection mode of the circuit breaker. If the pre-board connection mode is used, no special instructions are required. The user can directly connect the power line and the load line to the connection plate of the circuit breaker base before the circuit breaker is installed on the complete set of equipment, and use the screws to fasten the wiring.

2.Post-board wiring means that when the circuit breaker is installed in a complete set of equipment, the connection plate on the base of the circuit breaker is connected to the power line and the load line through the bolts of the mounting plate. Its greatest feature is that when replacing or repairing the circuit breaker, it is not necessary to re-wire and only the front stage power supply must be disconnected.

3. Plug-in wiring refers to the installation of a socket with six sockets on the mounting plate of the complete equipment, which is used in conjunction with the six sockets on the connection board of the circuit breaker.

4.Drawer type wiring is generally used for the installation of universal circuit breakers. The access drawer of the circuit breaker is completed by turning the rocker clockwise or counterclockwise. The main circuit and the secondary circuit adopt the plug-in structure, omitting the fixed installation. The necessary isolator can be used for one machine and two uses, improving the economical efficiency of use, and it also brings great convenience to operation and maintenance while increasing safety and reliability.

Precautions for the wiring of  MCCB(Molded Case Circuit Breakers)

1, the general circuit device, there are power and load signs above, in the actual wiring process, in accordance with the above logo on the line, do not reverse the two.
2. The control switch or the protection line must not pass through the current transformer. When the three-phase five-wire system or the single-phase three-wire system is adopted, the protection line must be connected to the protection main line of the leakage circuit breaker. If it is a single-phase lighting circuit, a three-phase four-wire distribution line, and other lines or equipment using a working neutral line, the neutral line must pass through the current transformer.
In the system where the neutral point of the transformer is directly grounded, once the leakage circuit breaker is installed, the working zero line can only be used as a working neutral line after passing through the current transformer, and it cannot be grounded repeatedly, nor can it work with other lines. The zero line is connected. The electrical equipment can only be connected to the load side of the leakage breaker. It is not allowed to connect one end to the load side and the other end to the power supply side.

 

 

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