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. 521-4692
Mfr. Part No.5SJ6520-6KS
BrandSiemens
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1 + N 20 A - Sentron 5SJ6 230 V, 400 V Type B 6 kA - 60V 90mm 36mm 76mm -
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3 20 A - Acti 9 iC60N 440 V Type C 6 kA - 144V - 54mm - -
RS Stock No. 791-3401
Mfr. Part No.A9F54350
PHP6,528.72
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3 50 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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Mfr. Part No.A9F54316
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3 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 54mm 78.5mm -
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2 10 A - xEffect FAZ 230 V Type S 10 kA - - 80mm 35mm 73.5mm -
RS Stock No. 746-8169
Mfr. Part No.2CDS272001R0021
BrandABB
PHP3,303.97
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2 2 A - System M Pro S200 400 V Type D 10 kA - - 88mm - 69mm -
RS Stock No. 622-0014
Mfr. Part No.5SY4102-7
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1 2 A - Sentron 5SY4 230 V, 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
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Mfr. Part No.A9F55220
PHP3,832.10
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2 20 A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415 V Type D 10 kA DIN Rail 100 → 133V 85mm 36mm 78.5mm -
RS Stock No. 776-3216
Mfr. Part No.A9N61534
PHP8,246.32
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2 30 A - Acti 9 C60H-DC - Type C 20 kA - 500V 36mm 73mm 81mm -
RS Stock No. 772-1325
Mfr. Part No.5SY4220-7
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PHP3,084.08
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2 20 A - Sentron 5SY4 400 V Type C 10 kA - - 90mm 36mm 76mm -
RS Stock No. 830-3067
Mfr. Part No.MGN61316
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2 5 A - - C60 480Y/277 V Type C 10 kA - 125V 12.86in 210.05mm 204.4mm -
RS Stock No. 772-1284
Mfr. Part No.5SY4204-8
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Mfr. Part No.S201-C4
BrandABB
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1 4 A - System M Pro S200 230 V Type C 6 kA - - 88mm 17.5mm 69mm -
RS Stock No. 776-3389
Mfr. Part No.A9F76210
PHP6,449.16
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RS Stock No. 776-3105
Mfr. Part No.A9N18393
PHP62,691.03
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4 125 A - Acti 9 C120N 440 V Type D 10 kA, 20 kA - ≤500V 108mm 73mm 81mm -
RS Stock No. 772-1290
Mfr. Part No.5SY4206-8
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PHP3,466.90
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RS Stock No. 772-1287
Mfr. Part No.5SY4202-8
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2 2 A - Sentron 5SY4 400 V Type D 10 kA - - 90mm 36mm 76mm -
RS Stock No. 776-3177
Mfr. Part No.A9N61512
PHP4,930.47
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1 20 A - Acti 9 C60H-DC - Type C 20 kA - 250V 18mm 73mm 81mm -
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Mfr. Part No.A9F84306
PHP2,142.46
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3 6 A - Acti 9 iC60H 440 V Type C 10 kA - 144V - 54mm - -
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Mfr. Part No.2CCS893001R0824
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