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 Length Width Depth Application
RS Stock No. 539-8201
Mfr. Part No.2CDS211001R0064
BrandABB
MYR72.37
Each
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1 6 A - System M Pro S200 440 V Type C 6 kA - 60V 85mm 17.5mm 69mm -
RS Stock No. 776-3102
Mfr. Part No.A9N18392
MYR4,408.93
Each
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4 100 A - Acti 9 C120N 440 V Type D 10 kA, 20 kA - ≤500V 108mm 73mm 81mm -
RS Stock No. 776-3345
Mfr. Part No.A9F76106
MYR261.21
Each
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1 6 A - Acti 9 iC60N 240 V Type B 10 kA - 72V 18mm - 85mm -
RS Stock No. 922-7128
Mfr. Part No.278975 & FAZ-C16/3N
BrandEaton
MYR628.67
Each
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3 16 A - xEffect FAZ 240 → 415 V Type C 10 kA - 96V 53.1mm 65.5mm 80mm Appliances, Business Equipment, Control Circuit, Lighting, Supplementary Protection
RS Stock No. 776-3109
Mfr. Part No.A9N21022
MYR192.61
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1 + N 4 A - Acti 9 DT40 240 V Type C 6 kA - - - - - -
RS Stock No. 527-9633
Mfr. Part No.S203-D32
BrandABB
MYR264.60
Each
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3 32 A - System M Pro S200 440 V Type D 6 kA - - - - 75.8mm -
RS Stock No. 734-9315
Mfr. Part No.A9F94425
MYR1,827.66
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4 25 A - Acti 9 iC60L 100 → 130 V, 12 → 60 V, 220 → 240 V, 380 → 415 V, 400 V, 440 V Type C 10 kA - 12 → 250V - 72mm - -
RS Stock No. 791-3146
Mfr. Part No.A9F53102
MYR158.56
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1 2 A - Acti 9 iC60H 100 → 133 V, 12 → 60 V, 220 → 240 V Type B 10 kA DIN Rail 72 V, 12 → 48 V 85mm 18mm 78.5mm -
RS Stock No. 624-0377
Mfr. Part No.278562 & FAZ-C20/1
BrandEaton
MYR91.77
Each
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1 20 A - xEffect FAZ 230 V Type C 10 kA - - 80mm 17.5mm 73.5mm -
RS Stock No. 776-8895
Mfr. Part No.A9F73116
MYR24.06
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1 16 A - Acti 9 iC60N 230 V, 400 V Type B 6 kA - 72V - 18mm - -
RS Stock No. 539-8380
Mfr. Part No.2CDS213001R0404
BrandABB
MYR240.66
Each
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3 40 A - System M Pro S200 440 V Type C 6 kA - - 85mm 52.5mm 69mm -
RS Stock No. 145-415
Mfr. Part No.16726
MYR119.10
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- - - - - - - - - - - - - -
RS Stock No. 776-3168
Mfr. Part No.A9N61504
MYR272.82
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1 4 A - Acti 9 C60H-DC - Type C 20 kA - 250V 18mm 73mm 81mm -
RS Stock No. 731-9755
Mfr. Part No.4 078 99
BrandLegrand
MYR679.10
Each
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4 20 A - DX Range DX3 230 V, 400 V Type C 10 kA - - - - - -
RS Stock No. 776-3496
Mfr. Part No.A9F77306
MYR729.13
Each
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3 6 A - Acti 9 iC60N 440 V Type C 6 kA - 180V - - 85mm -
RS Stock No. 791-3348
Mfr. Part No.A9F54220
MYR266.22
Each
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2 20 A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415 V Type C 10 kA DIN Rail 100 → 133V 85mm 36mm 78.5mm -
RS Stock No. 383-2024
Mfr. Part No.5SY4110-7
BrandSiemens
MYR96.59
Each
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1 10 A - Sentron 5SY4 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 776-3398
Mfr. Part No.A9F76216
MYR512.15
Each
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2 16 A - Acti 9 iC60N 440 V Type B 6 kA - 125V 36mm - 85mm -
RS Stock No. 772-1521
Mfr. Part No.A9N61528
MYR642.56
Each
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2 10 A - Acti 9 C60H-DC - Type C - - 500V - 36mm 73mm -
RS Stock No. 776-3105
Mfr. Part No.A9N18393
MYR5,157.88
Each
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4 125 A - Acti 9 C120N 440 V Type D 10 kA, 20 kA - ≤500V 108mm 73mm 81mm -
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