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. 791-3338
Mfr. Part No.A9F54204
TWD1,948.00
Each
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2 4 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415 V, 440 V Type C 10 kA DIN Rail 100 → 133V 85mm 36mm 78.5mm -
RS Stock No. 791-3473
Mfr. Part No.A9F55116
TWD607.00
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1 16 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240 V Type D 10 kA DIN Rail 12 → 48 V, 72 V 85mm 18mm 78.5mm -
RS Stock No. 772-1296
Mfr. Part No.5SY4206-7
BrandSiemens
TWD2,038.00
Each
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2 6 A - Sentron 5SY4 400 V Type C 10 kA - - 90mm 36mm 76mm -
RS Stock No. 622-0014
Mfr. Part No.5SY4102-7
BrandSiemens
TWD633.00
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1 2 A - Sentron 5SY4 230 V, 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 776-3216
Mfr. Part No.A9N61534
TWD5,373.00
Each
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2 30 A - Acti 9 C60H-DC - Type C 20 kA - 500V 36mm 73mm 81mm -
RS Stock No. 772-1319
Mfr. Part No.5SY4216-7
BrandSiemens
TWD1,856.00
Each
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2 16 A - Sentron 5SY4 400 V Type C 10 kA - - 90mm 36mm 76mm -
RS Stock No. 521-4951
Mfr. Part No.5SY6104-7
BrandSiemens
TWD620.00
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1 4 A - Sentron 5SY6 230 V, 400 V Type C 6 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 124-3156
Mfr. Part No.5SY4150-7
BrandSiemens
TWD1,562.00
Each
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1 50 A - Sentron 5SY4 230 V, 400 V Type C 10 kA - - 17.6mm 76.4mm 89.8mm Industrial, Plant Engineering
RS Stock No. 131-955
Mfr. Part No.2CDS272001R0324 - S202MC32
BrandABB
TWD1,538.00
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2 32 A - System M Pro S200 440 V Type C 10 kA - 125V 88mm 35mm 75.8mm -
RS Stock No. 776-3253
Mfr. Part No.A9F87232
TWD4,824.00
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2 32 A - Acti 9 iC60H 440 V Type C 10 kA - 125V - 78.5mm 85mm -
RS Stock No. 383-2024
Mfr. Part No.5SY4110-7
BrandSiemens
TWD471.00
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1 10 A - Sentron 5SY4 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 790-8863
Mfr. Part No.A9F44132
TWD660.00
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1 32 A - Acti 9 iC60N 12 → 60 V, 100 → 133 V, 220 → 240 V Type C 6 kA - 12 → 48 V, 72 V 18mm 85mm 78.5mm -
RS Stock No. 790-7361
Mfr. Part No.A9C65340
TWD9,510.00
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3 40 A - Acti 9 iC60H 220 → 240 V, 380 → 415 V Type C 10 kA - 24V - 84mm 77mm -
RS Stock No. 776-3449
Mfr. Part No.A9F74104
TWD1,917.00
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1 4 A - Acti 9 iC60N 240 V Type C 10 kA - 72V 18mm - 85mm -
RS Stock No. 239-4997
Mfr. Part No.7206.0000.3
BrandKopp
TWD265.00
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1 6 A - - GREEN ELECTRIC 230 → 400 V Type B 10 kA - 60V - - - -
RS Stock No. 746-7986
Mfr. Part No.S202-K6
BrandABB
TWD1,688.00
Each
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2 6 A - System M Pro S200 400 V Type K 6 kA - - 88mm 35mm 69mm -
RS Stock No. 814-7469
Mfr. Part No.60143
TWD6,131.00
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2 8 A - - C60 120 → 240 V Type C 10 kA rms @ 125 V dc, 20 kA rms @ 240 V ac - 125V 107mm 36mm 78.5mm -
RS Stock No. 814-7481
Mfr. Part No.60150
TWD6,469.00
Each
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2 35 A - - C60 120 → 240 V Type C 10 kA rms @ 125 V dc, 20 kA rms @ 240 V ac - 125V 107mm 36mm 78.5mm -
RS Stock No. 622-0036
Mfr. Part No.5SY4104-7
BrandSiemens
TWD557.00
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1 4 A - Sentron 5SY4 230 V, 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 624-0440
Mfr. Part No.FAZ-C20/3
BrandEaton
TWD1,783.00
Each
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3 20 A - XEffect FAZ 400 V Type C 10 kA - - 80mm 52.5mm 73.5mm -