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. 776-8968
Mfr. Part No.A9F74106
MYR24.06
Each
units
1 6 A - Acti 9 iC60N 230 V, 400 V Type C 6 kA - 72V - 18mm - -
RS Stock No. 776-3076
Mfr. Part No.A9N18369
MYR2,969.61
Each
units
3 125 A - Acti 9 C120N 440 V Type C 10 kA, 20 kA - ≤375V - - 81mm -
RS Stock No. 527-9649
Mfr. Part No.S203-D40
BrandABB
MYR317.72
Each
units
3 40 A - System M Pro S200 440 V Type D 6 kA - - - 52.5mm 75.8mm -
RS Stock No. 776-8860
Mfr. Part No.A9K24320
MYR115.16
Each
units
3 20 A - Acti 9 iK60N 400 V Type C 6000 A - - - 54mm - -
RS Stock No. 776-9080
Mfr. Part No.A9F74463
MYR451.04
Each
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4 63 A - Acti 9 iC60N 440 V Type C 6 kA - 250V - 72mm - -
RS Stock No. 776-3032
Mfr. Part No.A9N18480
MYR3,787.04
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4 100 A - Acti 9 C120H 440 V Type C 15 kA, 30 kA - ≤500V - 73mm 81mm -
RS Stock No. 776-9018
Mfr. Part No.A9F74232
MYR108.25
Each
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2 32 A - Acti 9 iC60N 440 V Type C 6 kA - 144V - 36mm - -
RS Stock No. 776-3433
Mfr. Part No.A9F74101
MYR263.20
Each
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1 1 A - Acti 9 iC60N 240 V Type C 10 kA - 72V 18mm 78.5mm 85mm -
RS Stock No. 776-9065
Mfr. Part No.A9F74410
MYR399.92
Each
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4 10 A - Acti 9 iC60N 440 V Type C 6 kA - 250V - 72mm - -
RS Stock No. 734-9065
Mfr. Part No.A9F77216
MYR306.43
Each
units
2 16 A - Acti 9 iC60N 100 → 130 V, 12 → 60 V, 220 → 240 V, 380 → 415 V, 400 V, 440 V Type C 6 kA - 12 → 144V - 36mm - -
RS Stock No. 776-3058
Mfr. Part No.A9N18362
MYR1,533.78
Each
units
2 100 A - Acti 9 C120N 440 V Type C 10 kA, 20 kA - ≤250V - - 81mm -
RS Stock No. 776-3054
Mfr. Part No.A9N18361
MYR1,385.87
Each
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2 80 A - Acti 9 C120N 440 V Type C 10 kA, 20 kA - ≤250V - - 81mm -
RS Stock No. 776-3161
Mfr. Part No.A9N61505
MYR331.81
Each
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1 5 A - Acti 9 C60H-DC - Type C 20 kA - 250V 18mm - 81mm -
RS Stock No. 847-3535
Mfr. Part No.FAZ-D16/3-NA
BrandEaton
MYR606.78
Each
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3 16 A - xEffect FAZ 240 → 415 V Type D 10 kA - - 53.1mm 105mm 75.5mm -
RS Stock No. 776-3442
Mfr. Part No.A9F77106
MYR202.65
Each
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1 6 A - Acti 9 iC60N 240 V Type C 10 kA - 72V - 78.5mm 85mm -
RS Stock No. 776-3159
Mfr. Part No.A9N61503
MYR315.24
Each
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1 3 A - Acti 9 C60H-DC - Type C 20 kA - 250V 18mm - 81mm -
RS Stock No. 776-8854
Mfr. Part No.A9K24306
MYR130.42
Each
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3 6 A - Acti 9 iK60N 400 V Type C 6000 A - - - 54mm - -
RS Stock No. 488-6836
Mfr. Part No.2CDS251001R0104 - S201C10
BrandABB
MYR79.73
Each
units
1 10 A - System M Pro S200 253 V Type C 6 kA - 72V 88mm 17.5mm 75.8mm -
RS Stock No. 734-9419
Mfr. Part No.A9F94216
MYR604.07
Each
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2 16 A - Acti 9 iC60L 400 V, 440 V, 100 → 130 V, 12 → 60 V, 220 → 240 V, 380 → 415 V Type C 10 kA - 12 → 144V - 36mm - -
RS Stock No. 791-3405
Mfr. Part No.A9F54363
MYR616.50
Each
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3 63 A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415 V Type C 10 kA DIN Rail 100 → 133V 85mm 54mm 78.5mm -
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