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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RS Stock No. 772-1521
Mfr. Part No.A9N61528
SGD184.94
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2 10 A - Acti 9 C60H-DC - Type C - - 500V - 36mm 73mm -
RS Stock No. 776-3073
Mfr. Part No.A9N18367
SGD846.31
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3 100 A - Acti 9 C120N 440 V Type C 10 kA, 20 kA - ≤375V 81mm 73mm 81mm -
RS Stock No. 776-3436
Mfr. Part No.A9F74102
SGD78.55
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1 2 A - Acti 9 iC60N 240 V Type C 10 kA - 72V 18mm 78.5mm 85mm -
RS Stock No. 776-9034
Mfr. Part No.A9F74320
SGD47.00
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3 20 A - Acti 9 iC60N 440 V Type C 6 kA - 144V - 54mm - -
RS Stock No. 776-9015
Mfr. Part No.A9F74225
SGD30.20
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2 25 A - Acti 9 iC60N 440 V Type C 6 kA - 144V - 36mm - -
RS Stock No. 776-8867
Mfr. Part No.A9K24332
SGD41.80
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3 32 A - Acti 9 iK60N 400 V Type C 6000 A - - - 54mm - -
RS Stock No. 776-8841
Mfr. Part No.A9F84363
SGD87.00
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3 63 A - Acti 9 iC60H 440 V Type C 10 kA - 144V - 54mm - -
RS Stock No. 776-3455
Mfr. Part No.A9F77116
SGD52.01
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1 16 A - Acti 9 iC60N 240 V Type C 10 kA - 72V - - 85mm -
RS Stock No. 776-9059
Mfr. Part No.A9F74350
SGD78.10
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3 50 A - Acti 9 iC60N 440 V Type C 6 kA - 144V - 54mm - -
RS Stock No. 776-3446
Mfr. Part No.A9F77110
SGD49.59
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1 10 A - Acti 9 iC60N 240 V Type C 10 kA - 72V - - 85mm -
RS Stock No. 776-3212
Mfr. Part No.A9N61532
SGD204.49
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2 20 A - Acti 9 C60H-DC - Type C 20 kA - 500V 36mm - 81mm -
RS Stock No. 776-3222
Mfr. Part No.A9N61539
SGD247.24
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2 63 A - Acti 9 C60H-DC - Type C 20 kA - 500V - - 81mm -
RS Stock No. 734-9065
Mfr. Part No.A9F77216
SGD102.83
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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. 791-3332
Mfr. Part No.A9F54206
SGD99.22
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RS Stock No. 776-3430
Mfr. Part No.A9F74103
SGD76.57
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1 3 A - Acti 9 iC60N 240 V Type C 10 kA - 72V - - 85mm -
RS Stock No. 791-3344
Mfr. Part No.A9F54216
SGD96.11
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2 16 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. 535-4352
Mfr. Part No.2CDS273001R0634
BrandABB
SGD140.29
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3 63 A - System M Pro S200 440 V Type C 10 kA - - 88mm - 75.8mm -
RS Stock No. 776-9062
Mfr. Part No.A9F74420
SGD111.70
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4 20 A - Acti 9 iC60N 440 V Type C 6 kA - 250V - 72mm - -
RS Stock No. 776-9074
Mfr. Part No.A9F74432
SGD111.70
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4 32 A - Acti 9 iC60N 440 V Type C 6 kA - 250V - 72mm - -
RS Stock No. 776-3067
Mfr. Part No.A9N18363
SGD596.32
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2 125 A - Acti 9 C120N 440 V Type C 10 kA, 20 kA - ≤250V 54mm 73mm 81mm -
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