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庫存編號 731-9443
製造零件編號4 067 73
BrandLegrand
HK$149.20
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BrandLegrand
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BrandLegrand
HK$693.50
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RS庫存編號 823-4664
製造零件編號4 067 82
BrandLegrand
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製造零件編號4 067 83
BrandLegrand
HK$219.82
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1 16 A - DX Range DNX3 250 V Type C 4.5 kA - 12V 77.7mm - 94.8mm -
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製造零件編號4 077 10
BrandLegrand
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1 + N 6 A - DX Range DX3 230 V Type C 10 kA - - - - - -
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BrandLegrand
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製造零件編號4 077 78
BrandLegrand
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BrandLegrand
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1 25 A - DX Range DNX3 250 V Type C 4.5 kA - 12V 77.7mm 17.8mm 94.8mm -
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4 40 A - DX Range DX3 230 V, 400 V Type C 10 kA - - - - - -
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3 40 A - DX Range DX3 230 V, 400 V Type C 10 kA - - - - - -
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製造零件編號0 225 03
BrandLegrand
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2 32 A - - Vistop 400 V - 5 kA - - 92mm 98.5mm 69.5mm -
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