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Common Question Answer of Residual Current Circuit Breaker

From: Quisure2019-09-28

1. What is a Residual Current Miniature Circuit Breaker?

Residual current circuit breaker is a device that protect against electric shock. It senses earth leakages and residual currents and ensures protection against electric shock. RCCB does not have overload and short circuit protection features built-in. Therefore, they are used in combination with MCB. RCCB is very common and can be found inside the panel board in houses.

RCCB is available in four poles and two poles only. The leakage current sensing range differs as 30mA, 100mA and 300mA. Also, current ratings of 20A, 25A, 40A, 50A, 63A, 80A, 100A and 125A are available. Since RCCB does not protect against short circuits, it does not have short-circuit withstand rating. It is highly recommended to use a short circuit protection device such as MCB or MCCB in series with RCCB.


2. What is a Residual Current Circuit Breaker with Overload?

Residual current circuit breaker with overload name RCBO, it is a combination of RCCB and MCB. It constitutes short circuit, overload and residual current protection features. It is designed to withstand short circuit currents and has arc chutes within.

It is used for the protection of devices like geyser etc. where the risk of electric shock and overload are more. RCBO is available in two poles and four poles. The leakage current sensing range of RCBO ranges as 10mA, 30mA, 100mA and 300mA. Also, current ratings include 20A, 25A, 40A, 63A, 80A, 100A and 125A. The short circuit breaking capacity breaking capacity of a RCBO varies up to 15kA.


3. What is an Isolator or Switch disconnector?

Isolators or Switch disconnector are devices used to isolate a circuit or equipment from the power supply during maintenance, in order to ensure the safety of workman. Isolators are offload devices, meaning the current flow through the isolator should be zero before the operation. So it do not offer any kind of protection to the circuit or device.


4. What is a Motor Protection Circuit Breaker?

Motor Protection Circuit Breaker name MPCB, it is a short circuit and overload protection device dedicated used for the safe operation of motors. But unlike MCCB and MCB, the trip characteristics of a MPCB allow the high inrush current during the motor start without allowing over current that may damage the motor winding. The short circuit capacity of MPCB is very high compared to that of MCB. Also, MPCB are more compact than MCCB. The over current set point of the MPCB can be adjusted as required. Moreover, MPCB can protect the motor against phase loss or phase imbalance. MPCB once tripped is must to be manually reset after the clearance of fault.

MPCB is available only in three poles and has a maximum short-circuit current withstand capability of 100kA. MPCB are a cost-effective and efficient solution to conventional motor starters, which use fuse-thermal overload relay combinations.


5. What is the difference between MCB, MCCB, RCCB, RCBO and Isolator?

Miniature Circuit Breaker name MCB – Short circuit and overload protection device, commonly used in the protection of household devices and devices with low short-circuit currents.

Moulded Case Circuit Breaker name MCCB – Short circuit and overload protection device, commonly used in the protection in low voltage power distribution and industrial equipment.

Motor Protection Circuit Breaker name MPCB – Short circuit, overload and phase loss protection device, used in motor starters of industry.

Residual Current Circuit Breaker name RCCB – Provides protection again electric shock and residual currents.

Residual Current Circuit Breaker with Overload name – Provides protection again electric shock, residual currents, short circuit and overload, commonly used in the protection of household devices and low short-circuit currents devices.

Isolator/ Switch Disconnector – Safety device, operated during maintenance or service of equipments.


6. What is the difference between MCB and RCBO?

Miniature Circuit Breaker name MCB and Residual Current Circuit Breaker name RCCB with Overload Protection are circuit protection devices. These devices are commonly used in low voltage power distribution and can be seen in distribution boards in house, offices, commercial buildings etc.

RCBO are available in two poles (L + N), single pole with solid neutral and four poles (L+L+L+N) versions. A series connection of short circuit protection devices such as MCB or MCCB and earth fault or Residual current protection device such as ELCB or RCCB can be used as an alternative to RCBO.

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