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. 176-706
Mfr. Part No.S401M-B20
BrandABB
$51.97
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units
1 20 A - Smissline S400 230 V, 400 V Type B 10 kA - 60V 91mm 18mm 97mm -
RS Stock No. 746-7554
Mfr. Part No.S201-B63
BrandABB
$29.30
Each
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1 63 A - System M Pro S200 230 V Type B 6 kA - - - - 69mm -
RS Stock No. 790-8715
Mfr. Part No.A9F55404
$335.46
Each
units
4 4 A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415 V Type D 10 kA - 220 → 250V 72mm 85mm 78.5mm -
RS Stock No. 922-6908
Mfr. Part No.FAZ-C10/1-NA
BrandEaton
$44.54
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1 10 A - xEffect FAZ 240 → 415 V Type C 10 kA - 48V 17.8mm 65.5mm 80mm Computers, Control Instrumentation, External Load Circuit, HACR Internal/External Equipment, Internal/External Convenience Receptacle Circuit, Motor Control Circuit, PLC I/O Point, Power Conditioner, Power Supplies, Relay, Uninterruptable Power Supplies
RS Stock No. 791-3477
Mfr. Part No.A9F55120
$46.76
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1 20 A - Acti 9 iC60H 100 → 133 V, 12 → 60 V, 220 → 240 V Type D 10 kA DIN Rail 72 V, 12 → 48 V 85mm 18mm 78.5mm -
RS Stock No. 383-2052
Mfr. Part No.5SY4120-7
BrandSiemens
$32.92
Each
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1 20 A - Sentron 5SY4 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 521-4973
Mfr. Part No.5SY6305-7
BrandSiemens
$162.93
Each
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3 500 mA - Sentron 5SY6 400 V Type C 6 kA - - 89.8mm 52.8mm 76mm -
RS Stock No. 791-3212
Mfr. Part No.A9F53250
$140.16
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2 50 A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415 V Type B 10 kA DIN Rail 100 → 133V 85mm 36mm 78.5mm -
RS Stock No. 859-6149
Mfr. Part No.0830925
$25.94
1 Box of 10
Box(es)
- - - - UM1-TM (3.5X12) - - - - - - - - -
RS Stock No. 521-4793
Mfr. Part No.5SJ6220-6KS
BrandSiemens
$11.70
Each
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2 20 A - Sentron 5SJ6 230 V, 400 V Type B 6 kA - 60V 90mm 36mm 76mm -
RS Stock No. 435-207
Mfr. Part No.2CCS862001R0845
BrandABB
$378.78
Each
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2 125 A - High Performance S800 400 V, 690 V Type B 50 kA - 250V - 53mm 88.5mm -
RS Stock No. 746-7740
Mfr. Part No.S203-C2
BrandABB
$119.80
Each
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3 2 A - System M Pro S200 400 V Type C 6 kA - - 88mm 52.5mm 69mm -
RS Stock No. 776-2314
Mfr. Part No.A9F07220
$143.18
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2 20 A - Acti 9 iC60H 440 V Type C 10 kA - 133V 36mm 78.5mm 91mm -
RS Stock No. 178-724
Mfr. Part No.S403M-C2
BrandABB
$303.02
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3 2 A - Smissline S400 230 V, 400 V Type C 10 kA - - 91mm 54mm 97mm -
RS Stock No. 776-2452
Mfr. Part No.A9F07610
$140.85
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1 + N 10 A - Acti 9 iC60H 230 V, 400 V Type C 10 kA - 72V 36mm 78.5mm 91mm -
RS Stock No. 772-1265
Mfr. Part No.5SY4120-8
BrandSiemens
$55.72
Each
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1 20 A - Sentron 5SY4 230/400 V Type D 10 kA - - 89.8mm 17.6mm 76.4mm -
RS Stock No. 791-3559
Mfr. Part No.A9F55302
$242.19
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3 2 A - Acti 9 iC60H 440 V, 12 → 133 V, 220 → 240 V, 380 → 415 V Type D 10 kA DIN Rail 100 → 133V 85mm 54mm 78.5mm -
RS Stock No. 535-4172
Mfr. Part No.2CDS271001R0254
BrandABB
$32.68
Each
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1 25 A - System M Pro S200 253 V Type C 10 kA - 72V 88mm 17.5mm 75.8mm -
RS Stock No. 124-3220
Mfr. Part No.5SY4563-7
BrandSiemens
$186.44
Each
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1 + N 63 A - Sentron 5SY4 230 V Type C 10 kA - - 35.2mm 76mm 89.8mm Industrial, Plant Engineering
RS Stock No. 436-5733
Mfr. Part No.7216.0200.6
BrandKopp
$34.58
Each
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1 16 A - - GREEN ELECTRIC 230 → 400 V Type D 10 kA - 60V - - - -
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