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. 772-1303
Mfr. Part No.5SY4210-7
BrandSiemens
HK$744.49
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units
2 10 A - Sentron 5SY4 400V Type C - - 10 kA 90mm 36mm 76mm -
RS Stock No. 383-2024
Mfr. Part No.5SY4110-7
BrandSiemens
HK$268.74
Each
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1 10 A - Sentron 5SY4 400V Type C - - 10 kA 89.8mm 17.6mm 76.4mm -
RS Stock No. 539-8223
Mfr. Part No.2CDS211001R0164 SH201-C16
BrandABB
HK$126.36
Each
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1 16 A - System M Pro S200 440V Type C - 60V 6 kA 85mm 17.5mm 69mm -
RS Stock No. 776-3345
Mfr. Part No.A9F76106
HK$477.32
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1 6 A - Acti 9 iC60N 240V Type B - 72V 10 kA 18mm - 85mm -
RS Stock No. 734-9450
Mfr. Part No.A9N21369
HK$836.67
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- 32 A - Acti 9 DT40 400V Type C - - 6 kA - - - -
RS Stock No. 791-3401
Mfr. Part No.A9F54350
HK$1,153.33
Each
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3 50 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. 488-7457
Mfr. Part No.2CDS251001R0065 - S201B6
BrandABB
HK$149.23
Each
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1 6 A - System M Pro S200 253V Type B - 72V 6 kA 88mm 17.5mm 75.8mm -
RS Stock No. 746-7637
Mfr. Part No.2CDS254001R0635 S204-B63
BrandABB
HK$1,767.75
Each
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4 63 A - System M Pro S200 400V Type B - - 6 kA - 70mm 69mm -
RS Stock No. 746-8107
Mfr. Part No.2CDS274001R0635 S204M-B63
BrandABB
HK$1,364.82
Each
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4 63 A - System M Pro S200 400V Type B - - 10 kA 83mm 70mm 74.8mm -
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. 734-9276
Mfr. Part No.A9F77263
HK$1,588.11
Each
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2 63 A - Acti 9 iC60N 12 → 60 V, 100 → 130 V, 220 → 240 V, 380 → 415V, 400 V, 440 V Type C - 12 → 144V 6 kA - 36mm - -
RS Stock No. 539-8267
Mfr. Part No.2CDS211001R0404 SH201-C40
BrandABB
HK$131.45
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1 40 A - System M Pro S200 440V Type C - 60V 6 kA 85mm 17.5mm 69mm -
RS Stock No. 791-3297
Mfr. Part No.A9F54116
HK$253.91
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1 16 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. 776-3216
Mfr. Part No.A9N61534
HK$1,181.07
Each
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2 30 A - Acti 9 C60H-DC - Type C - 500V 20 kA 36mm 73mm 81mm -
RS Stock No. 734-9295
Mfr. Part No.A9F87216
HK$1,129.38
Each
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2 16 A - Acti 9 iC60H 12 → 60 V, 100 → 130 V, 220 → 240 V, 380 → 415 V, 400 V, 440V Type C - 12 → 144V 10 kA - - - -
RS Stock No. 776-3294
Mfr. Part No.A9F87340
HK$2,958.64
Each
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3 40 A - Acti 9 iC60H 440V Type C - 180V 10 kA - - 85mm -
RS Stock No. 825-5712
Mfr. Part No.P1MB2PC06
BrandLovato
HK$341.64
Each
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2 6 A - ModuLo P1MB 230 V, 400V Type C - 80V 10 kA 86.5mm 36mm 79.52mm -
RS Stock No. 825-5949
Mfr. Part No.P1MB4PB63
BrandLovato
HK$911.64
Each
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4 63 A - ModuLo P1MB 230 V, 400V Type B - - 10 kA 86.5mm 72mm 79.52mm -
RS Stock No. 791-3385
Mfr. Part No.A9F54306
HK$1,193.33
Each
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3 6 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. 791-3344
Mfr. Part No.A9F54216
HK$769.22
Each
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2 16 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 -