MCBs

MCBs, or miniature circuit breakers, are a type of switch used to automatically turn off electrical circuits during abnormal conditions. MCBs often replace fuses in low voltage electrical circuits as they can be more reliable, much more sensitive and are resettable.


How an MCB Works


When continuous overcurrent flows through an MCB, a bimetallic strip is heated and causes it to bend. This bending of the bimetallic strip releases a mechanical latch opening the contacts and turning off the MCB, thereby stopping the current to flow in the circuit. To restart the flow of current the MCB must be manually turned on. This mechanism protects the MCB from faults arising due to overcurrent or overload and is intended to prevent the accidental overloading of the cable in a no-fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB. The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one-tenth of a second. The level of this magnetic trip gives the MCB its type characteristic.


MCBs are used to perform many functions such as local control switches, isolating switches against faults and overload protection devices for installation or specific equipment or appliances.


MCB Types


MCBs have three common types for circuit protection in residential, commercial and industrial applications. The use is classified by a type, which determines the tripping characteristics of the MCB:


Type B - trips between 3 and 5 times the load current


This type will trip instantly at a rate of three to five times its rated current. These are normally used for resistive or small inductive loads where switching surges are very small. Therefore, these are suitable for residential or light commercial installations.


Type C - trips between 5 and 10 times the full load current


This type will trip instantly at a rate of five to ten times its rated current. These are normally used for high inductive loads where switching surges are high such as small motors and fluorescent lighting. In such cases, type C MCBs are preferred to handle higher value of short circuit currents. Therefore, these are suitable for highly inductive commercial and industrial installations.


Type D - trips between 10 and 20 times the full load current


This type will trip instantly at a rate of ten to twenty-five times its rated current. These are normally used for very high inductive loads where high inrush current is very frequent. These are suitable for specific industrial and commercial applications. The common examples of such applications include x-ray machines, UPS systems, industrial welding equipment, large winding motors, etc.


How to select a suitable MCB for the application?


Focus on 3 main points to choose the right MCB for the electrical circuit


  1. Ampere rating

  2. Short circuit breaking capacity

  3. Application type

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Description Price Number of Poles Current Rating Model Number Range Series Rated AC Voltage Tripping Characteristics Mounting Style Rated DC Voltage Breaking Capacity at Maximum Voltage Rating Length Width Depth Break Time
RS庫存編號 729-9052
製造零件編號C68N 2P 16A (HK)
HK$238.46
單位
2 16 A - Multi 9 C68N 415V - - - 6 kA 81mm 36mm 75.5mm -
RS庫存編號 776-3064
製造零件編號A9N18365
HK$3,474.48
單位
3 80 A - Acti 9 C120N 440V Type C - ≤375V 10 kA, 20 kA 81mm 73mm 81mm -
RS庫存編號 776-3168
製造零件編號A9N61504
HK$683.41
單位
1 4 A - Acti 9 C60H-DC - Type C - 250V 20 kA 18mm 73mm 81mm -
RS庫存編號 791-3332
製造零件編號A9F54206
HK$835.41
單位
2 6 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415V, 440 V Type C DIN Rail 100 → 133V 10 kA 85mm 36mm 78.5mm -
RS庫存編號 791-3307
製造零件編號A9F54120
HK$253.91
單位
1 20 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240V Type C DIN Rail 12 → 48V, 72 V 10 kA 85mm 18mm 78.5mm -
RS庫存編號 776-3385
製造零件編號A9F76206
HK$1,058.39
單位
2 6 A - Acti 9 iC60N 440V Type B - 125V 6 kA - 78.5mm 85mm -
RS庫存編號 776-3398
製造零件編號A9F76216
HK$830.31
單位
2 16 A - Acti 9 iC60N 440V Type B - 125V 6 kA 36mm - 85mm -
RS庫存編號 791-3341
製造零件編號A9F54210
HK$760.82
單位
2 10 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415V, 440 V Type C DIN Rail 100 → 133V 10 kA 85mm 36mm 78.5mm -
RS庫存編號 791-3405
製造零件編號A9F54363
HK$1,476.86
單位
3 63 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415V, 440 V Type C DIN Rail 100 → 133V 10 kA 85mm 54mm 78.5mm -
RS庫存編號 734-9286
製造零件編號A9F87210
HK$1,073.59
單位
2 10 A - Acti 9 iC60H 12 → 60 V, 100 → 130 V, 220 → 240 V, 380 → 415V, 400 V, 440 V Type C - 12 → 144V 10 kA - - - -
RS庫存編號 791-3354
製造零件編號A9F54240
HK$709.23
單位
2 40 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415V, 440 V Type C DIN Rail 100 → 133V 10 kA 85mm 36mm 78.5mm -
RS庫存編號 791-3284
製造零件編號A9F54102
HK$343.42
單位
1 2 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240V Type C DIN Rail 12 → 48V, 72 V 10 kA 85mm 18mm 78.5mm -
RS庫存編號 776-3354
製造零件編號A9F76110
HK$422.17
單位
1 10 A - Acti 9 iC60N 240V Type B - 72V 10 kA - - 85mm -
RS庫存編號 776-3458
製造零件編號A9F77120
HK$301.31
單位
1 20 A - Acti 9 iC60N 240V Type C - 72V 10 kA - 78.5mm 85mm -
RS庫存編號 791-3290
製造零件編號A9F54106
HK$284.19
單位
1 6 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240V Type C DIN Rail 12 → 48V, 72 V 10 kA 85mm 18mm 78.5mm -
RS庫存編號 776-3073
製造零件編號A9N18367
HK$5,426.04
單位
3 100 A - Acti 9 C120N 440V Type C - ≤375V 10 kA, 20 kA 81mm 73mm 81mm -
RS庫存編號 791-3293
製造零件編號A9F54110
HK$253.91
單位
1 10 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240V Type C DIN Rail 12 → 48V, 72 V 10 kA 85mm 18mm 78.5mm -
RS庫存編號 734-9141
製造零件編號A9F77310
HK$1,112.22
單位
3 10 A - Acti 9 iC60N 12 → 60 V, 100 → 130 V, 220 → 240 V, 380 → 415 V, 400 V, 440V Type C - 12 → 144V 6 kA - - - -
RS庫存編號 734-9450
製造零件編號A9N21369
HK$836.67
單位
- 32 A - Acti 9 DT40 400V Type C - - 6 kA - - - -
RS庫存編號 776-3216
製造零件編號A9N61534
HK$1,020.26
單位
2 30 A - Acti 9 C60H-DC - Type C - 500V 20 kA 36mm 73mm 81mm -