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. 776-3294
Mfr. Part No.A9F87340
HK$2,958.64
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3 40 A - Acti 9 iC60H 440V Type C - 180V 10 kA - - 85mm -
RS Stock No. 132-071
Mfr. Part No.2CDS272001R0104 S202M-C10
BrandABB
HK$424.29
Each
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2 10 A - System M Pro S200 440V Type C - 125V 10 kA 88mm 35mm 75.8mm -
RS Stock No. 847-3241
Mfr. Part No.278756 & FAZ-C10/2
BrandEaton
HK$457.69
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2 10 A - XEffect FAZ 240 → 415V Type C - - 10 kA 36mm 84.7mm 72.6mm -
RS Stock No. 488-6943
Mfr. Part No.2CDS251001R0325 - S201B32
BrandABB
HK$137.31
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1 32 A - System M Pro S200 253V Type B - 72V 6 kA 88mm 17.5mm 75.8mm -
RS Stock No. 731-9443
Mfr. Part No.4 067 73
BrandLegrand
HK$113.66
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- 10 A - DX Range DNX3 - Type C - - 4.5 kA - - - -
RS Stock No. 849-6563
Mfr. Part No.EUC2P63C
BrandEuropa
HK$144.34
Each
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2 63 A - EU EUC 230/400V Type C - - 10 kA 36mm 78mm 87mm -
RS Stock No. 922-6945
Mfr. Part No.132702 & FAZ-B10/2-NA
BrandEaton
HK$667.89
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2 10 A - XEffect FAZ 240 → 415V Type B - 48V 10 kA 35.4mm 65.5mm 80mm Instantaneous
RS Stock No. 539-8251
Mfr. Part No.2CDS211001R0324 SH201-C32
BrandABB
HK$126.36
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1 32 A - System M Pro S200 440V Type C - 60V 6 kA 85mm 17.5mm 69mm -
RS Stock No. 791-3578
Mfr. Part No.A9F55340
HK$1,282.93
Each
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3 40 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415V, 440 V Type D DIN Rail 100 → 133V 10 kA 85mm 54mm 78.5mm -
RS Stock No. 791-3382
Mfr. Part No.A9F54316
HK$1,118.83
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3 16 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. 791-3473
Mfr. Part No.A9F55116
HK$180.43
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1 16 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240V Type D DIN Rail 12 → 48V, 72 V 10 kA 85mm 18mm 78.5mm -
RS Stock No. 746-7716
Mfr. Part No.2CDS252001R0164 S202-C16
BrandABB
HK$377.92
Each
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2 16 A - System M Pro S200 400V Type C - - 6 kA - - 69mm -
RS Stock No. 790-8850
Mfr. Part No.A9F44106
HK$243.47
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1 6 A - Acti 9 iC60N 12 → 60 V, 100 → 133 V, 220 → 240V Type C - 12 → 48 V, 72V 6 kA - 85mm 78.5mm -
RS Stock No. 791-3304
Mfr. Part No.A9F54132
HK$266.74
Each
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1 32 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. 849-6516
Mfr. Part No.EUC1P20C
BrandEuropa
HK$63.19
Each
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1 20 A - EU EUC 230/400V Type C - - 10 kA 18mm 78mm 87mm -
RS Stock No. 535-4289
Mfr. Part No.2CDS273001R0164 S203M-C16
BrandABB
HK$509.83
Each
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3 16 A - System M Pro S200 440V Type C - - 10 kA - 52.5mm 75.8mm -
RS Stock No. 776-3442
Mfr. Part No.A9F77106
HK$383.83
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1 6 A - Acti 9 iC60N 240V Type C - 72V 10 kA - 78.5mm 85mm -
RS Stock No. 622-0187
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BrandSiemens
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1 500 mA - Sentron 5SY7 230 V, 400V Type C - - 15 kA 89.8mm 17.6mm 76.4mm -
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Each
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1 16 A - EU EUC 230/400V Type C - - 10 kA 18mm 78mm 87mm -
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Mfr. Part No.A9F53306
HK$1,268.01
Each
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3 6 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415V, 440 V Type B DIN Rail 100 → 133V 10 kA 85mm 54mm 78.5mm -