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. 731-9685
Mfr. Part No.4 076 95
BrandLegrand
SGD153.24
Each
units
- 4 A - DX Range DX3 230V Type C - - 10 kA - - - -
RS Stock No. 731-9566
Mfr. Part No.4 077 15
BrandLegrand
SGD128.70
Each
units
- 20 A - DX Range DX3 230V Type C - - 10 kA - - - -
RS Stock No. 731-9755
Mfr. Part No.4 078 99
BrandLegrand
SGD272.74
Each
units
4 20 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 731-9471
Mfr. Part No.4 076 98
BrandLegrand
SGD119.07
Each
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- 10 A - DX Range DX3 230V Type C - - 10 kA - - - -
RS Stock No. 731-9455
Mfr. Part No.4 067 75
BrandLegrand
SGD19.33
Each
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- 20 A - DX Range DNX3 - Type C - - 4.5 kA - - - -
RS Stock No. 731-9679
Mfr. Part No.4 076 92
BrandLegrand
SGD172.45
Each
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- 1 A - DX Range DX3 230V Type C - - 10 kA - - - -
RS Stock No. 731-9487
Mfr. Part No.4 077 84
BrandLegrand
SGD125.17
Each
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2 16 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 731-9714
Mfr. Part No.4 077 87
BrandLegrand
SGD136.55
Each
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2 32 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 731-9718
Mfr. Part No.4 078 27
BrandLegrand
SGD202.22
Each
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3 10 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 823-4668
Mfr. Part No.4 067 83
BrandLegrand
SGD37.63
Each
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1 16 A - DX Range DNX3 250V Type C - 12V 4.5 kA 77.7mm - 94.8mm -
RS Stock No. 731-9724
Mfr. Part No.4 078 31
BrandLegrand
SGD167.18
Each
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3 25 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 731-9660
Mfr. Part No.4 076 50
BrandLegrand
SGD75.14
Each
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1 6 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 823-4674
Mfr. Part No.4 068 81
BrandLegrand
SGD38.65
Each
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1 10 A - DX Range DX3 250V Type C - 12V 4.5 kA - 17.8mm 94.8mm -
RS Stock No. 620-2965
Mfr. Part No.0 225 53
BrandLegrand
SGD468.75
Each
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4 160 A - - Vistop 400V - - - 15 kA 90mm 125mm 104mm -
RS Stock No. 731-9452
Mfr. Part No.4 067 74
BrandLegrand
SGD19.33
Each
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- 16 A - DX Range DNX3 - Type C - - 4.5 kA - - - -
RS Stock No. 731-9792
Mfr. Part No.4 062 66
BrandLegrand
SGD135.69
Each
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- 6 A - - DX3 250 V - - - - - - - -
RS Stock No. 731-9733
Mfr. Part No.4 078 32
BrandLegrand
SGD221.59
Each
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3 32 A - DX Range DX3 - Type C - - 10 kA - - - -
RS Stock No. 823-4670
Mfr. Part No.4 067 86
BrandLegrand
SGD47.51
Each
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1 32 A - DX Range DNX3 250V Type C - 12V 4.5 kA 77.7mm 17.8mm 94.8mm -
RS Stock No. 731-9705
Mfr. Part No.4 077 78
BrandLegrand
SGD211.91
Each
units
2 3 A - DX Range DX3 230 V, 400V Type C - - 10 kA - - - -
RS Stock No. 731-9698
Mfr. Part No.4 077 03
BrandLegrand
SGD165.98
Each
units
- 32 A - DX Range DX3 230V Type C - - 10 kA - - - -