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 Breaking Capacity Mounting Style Rated DC Voltage Breaking Capacity at Maximum Voltage Rating Length Width Depth
RS Stock No. 772-1366
Mfr. Part No.5SY4306-7
BrandSiemens
$240.54
Each
units
3 6A - Sentron 5SY4 400V Type C - - - 10 kA 89.8mm 52.8mm 76mm
RS Stock No. 132-116
Mfr. Part No.2CDS272001R0204
BrandABB
$98.63
Each
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2 20 A - System M Pro S200 440 V Type C 10 kA - 125V - 88mm 35mm 75.8mm
RS Stock No. 791-3350
Mfr. Part No.A9F54232
$125.68
Each
units
2 32A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415V Type C - DIN Rail 100 → 133V 10 kA 85mm 36mm 78.5mm
RS Stock No. 791-3467
Mfr. Part No.A9F55104
$51.27
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1 4A - Acti 9 iC60H 100 → 133 V, 12 → 60 V, 220 → 240V Type D - DIN Rail 72 V, 12 → 48V 10 kA 85mm 18mm 78.5mm
RS Stock No. 849-6563
Mfr. Part No.EUC2P63C
BrandEuropa
$24.67
Each
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2 63A - EU EUC 230/400V Type C - - - 10 kA 36mm 78mm 87mm
RS Stock No. 849-6591
Mfr. Part No.EUC3P32C
BrandEuropa
$40.22
Each
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3 32A - EU EUC 230/400V Type C - - - 10 kA 54mm 78mm 87mm
RS Stock No. 825-6157
Mfr. Part No.P2MB2PC100
BrandLovato
$173.19
Each
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2 100A - ModuLo P2MB 230 V, 400V Type C - - 60V 10 kA 85mm 54mm 80mm
RS Stock No. 791-3275
Mfr. Part No.A9F54101
$56.03
Each
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1 1A - Acti 9 iC60H 100 → 133 V, 12 → 60 V, 220 → 240V Type C - DIN Rail 72 V, 12 → 48V 10 kA 85mm 18mm 78.5mm
RS Stock No. 535-6112
Mfr. Part No.2CDS273001R0255
BrandABB
$149.39
Each
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3 25A - System M Pro S200 440V Type B - - - 10 kA 88mm - 75.8mm
RS Stock No. 849-6474
Mfr. Part No.EUC1P25B
BrandEuropa
$14.39
Each
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1 25A - EU EUB 230/400V Type B - - - 10 kA 18mm 78mm 87mm
RS Stock No. 825-5671
Mfr. Part No.P1MB2PB16
BrandLovato
$62.08
Each
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2 16A - ModuLo P1MB 230 V, 400V Type B - - 80V 10 kA 86.5mm 36mm 79.52mm
RS Stock No. 539-8273
Mfr. Part No.2CDS213001R0065
BrandABB
$73.87
Each
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3 6A - System M Pro S200 440V Type B - - - 6 kA 85mm 52.5mm 69mm
RS Stock No. 622-0424
Mfr. Part No.5SY7325-6
BrandSiemens
$150.17
Each
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3 25A - Sentron 5SY7 400V Type B - - - 15 kA 89.8mm 52.8mm 76mm
RS Stock No. 790-8872
Mfr. Part No.A9F44140
$49.53
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1 40A - Acti 9 iC60N 100 → 133 V, 12 → 60 V, 220 → 240V Type C - - 12 → 48 V, 72V 6 kA 18mm - 78.5mm
RS Stock No. 746-7609
Mfr. Part No.S203-B40
BrandABB
$93.80
Each
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3 40A - System M Pro S200 400V Type B - - - 6 kA 88mm 52.5mm 69mm
RS Stock No. 131-927
Mfr. Part No.2CDS272001R0255
BrandABB
$69.81
Each
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2 25 A - System M Pro S200 440 V Type B 10 kA - 125V - 88mm 35mm 75.8mm
RS Stock No. 825-6006
Mfr. Part No.P1MB4PD32
BrandLovato
$130.98
Each
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4 32A - ModuLo P1MB 230 V, 400V Type D - - - 10 kA 86.5mm 72mm 79.52mm
RS Stock No. 488-6886
Mfr. Part No.2CDS252001R0205 - S202B20
BrandABB
$75.19
Each
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2 20A - System M Pro S200 440V Type B - - 125V 6 kA 88mm 35mm 75.8mm
RS Stock No. 229-7919
Mfr. Part No.ALB501
BrandEaton
$26.09
Each
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1 50A - Memera ALB - Type B - - - - - - -
RS Stock No. 849-6484
Mfr. Part No.EUC1P63B
BrandEuropa
$14.04
Each
units
1 63A - EU EUB 230/400V Type B - - - 10 kA 18mm 78mm 87mm