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 Stock No. 729-9052
Mfr. Part No.C68N 2P 16A (HK)
HK$238.46
Each
units
2 16 A - Multi 9 C68N 415V - - - 6 kA 81mm 36mm 75.5mm -
RS Stock No. 132-009
Mfr. Part No.2CDS272001R0024
BrandABB
HK$547.87
Each
units
2 2 A - System M Pro S200 440V Type C - 125V 10 kA 88mm 35mm 75.8mm -
RS Stock No. 535-4150
Mfr. Part No.2CDS271001R0164
BrandABB
HK$150.93
Each
units
1 16 A - System M Pro S200 253V Type C - 72V 10 kA 88mm 17.5mm 75.8mm -
RS Stock No. 776-3064
Mfr. Part No.A9N18365
HK$3,860.53
Each
units
3 80 A - Acti 9 C120N 440V Type C - ≤375V 10 kA, 20 kA 81mm 73mm 81mm -
RS Stock No. 535-4188
Mfr. Part No.2CDS271001R0324
BrandABB
HK$165.35
Each
units
1 32 A - System M Pro S200 253V Type C - 72V 10 kA 88mm 17.5mm 75.8mm -
RS Stock No. 776-3168
Mfr. Part No.A9N61504
HK$673.97
Each
units
1 4 A - Acti 9 C60H-DC - Type C - 250V 20 kA 18mm 73mm 81mm -
RS Stock No. 791-3332
Mfr. Part No.A9F54206
HK$768.47
Each
units
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 Stock No. 131-983
Mfr. Part No.2CDS272001R0044
BrandABB
HK$538.03
Each
units
2 4 A - System M Pro S200 440V Type C - 125V 10 kA 88mm 35mm 75.8mm -
RS Stock No. 791-3307
Mfr. Part No.A9F54120
HK$233.57
Each
units
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 Stock No. 489-6625
Mfr. Part No.5SY6106-7
BrandSiemens
HK$281.36
Each
units
1 6 A - Sentron 5SY6 230 V, 400V Type C - - 6 kA 89.8mm 17.6mm 76.4mm -
RS Stock No. 776-3385
Mfr. Part No.A9F76206
HK$1,058.39
Each
units
2 6 A - Acti 9 iC60N 440V Type B - 125V 6 kA - 78.5mm 85mm -
RS Stock No. 864-4352
Mfr. Part No.242405 & PLSM-C16/2-MW
HK$412.70
Each
units
2 16 A - XPole PLSM - Type C - 48V 10 kA 35mm 80mm 75mm -
RS Stock No. 791-3405
Mfr. Part No.A9F54363
HK$1,322.66
Each
units
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 Stock No. 791-3341
Mfr. Part No.A9F54210
HK$699.85
Each
units
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 Stock No. 132-122
Mfr. Part No.2CDS272001R0164
BrandABB
HK$406.68
Each
units
2 16 A - System M Pro S200 440V Type C - 125V 10 kA 88mm 35mm 75.8mm -
RS Stock No. 776-3398
Mfr. Part No.A9F76216
HK$922.57
Each
units
2 16 A - Acti 9 iC60N 440V Type B - 125V 6 kA 36mm - 85mm -
RS Stock No. 734-9286
Mfr. Part No.A9F87210
HK$1,055.83
Each
units
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 Stock No. 847-3245
Mfr. Part No.102167 & FAZ-C10/2-NA
BrandEaton
HK$718.01
Each
units
2 10 A - XEffect FAZ 240 → 415V Type C - - 10 kA 35.4mm 105mm 75.5mm -
RS Stock No. 772-1366
Mfr. Part No.5SY4306-7
BrandSiemens
HK$470.36
Each
units
3 6 A - Sentron 5SY4 400V Type C - - 10 kA 89.8mm 52.8mm 76mm -
RS Stock No. 825-5762
Mfr. Part No.P1MB2PD20
BrandLovato
HK$259.03
Each
units
2 20 A - ModuLo P1MB 230 V, 400V Type D - 80V 10 kA 86.5mm 36mm 79.52mm -
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