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Residual Current Circuit Breakers (RCCBs): Safeguarding Against Fault Currents

Exporelec > Blog > Electric > Residual Current Circuit Breakers (RCCBs): Safeguarding Against Fault Currents
Dec 22, 2023 Posted by: Exporelec Electric Electric

Understanding Circuit Breakers

Circuit breakers serve as protective devices designed to prevent damage resulting from excessive current in the system caused by potential faults.

Introduction to Residual Current Circuit Breakers (RCCBs)

A Residual Current Circuit Breaker (RCCB) functions to identify leakage current within the system and swiftly interrupt the circuit, thereby safeguarding individuals and installations from potential hazards within milliseconds.

Operational Mechanism of Residual Current Circuit Breakers (RCCBs)

RCCBs operate on the fundamental principle of Kirchhoff’s Law, which ensures equilibrium between incoming and outgoing currents. A toroidal current transformer within the RCCB continuously monitors both incoming and outgoing currents. If a disparity emerges between the two, indicating a leakage, the toroid transmits this information to the RCCB, triggering the opening of the main contacts.

Residual Current Circuit Breaker iID, 4P, 63A, 30mA, Tip A

Types and Ratings 

Types WaveForm
AC Sensitive to residual sinusoidal alternating current only
A Sensitive to residual alternating current and/or pulsating direct current
B Provide protection of alternating residual sinusoidal current up to 1000Hz, pulsating direct current and smooth direct residual currents.
F Provide protection for circuit using single phased variable speed drivers could be used.

Vulnerability and Sensitivity of RCCBs

Human tolerance to electrical discharge stands at approximately 30 milliamps. While sensations might start at 10 mA, muscle spasms and respiratory paralysis can occur beyond 30 mA. RCCBs are engineered to detect even minuscule changes in residual power to ensure swift protection.

Selection Criteria for RCCBs

Proper selection and application of RCCBs prove to be simple, cost-effective, and reliable means of safeguarding both humans and electrical equipment. Key selection criteria encompass:

1- Number of Poles: 2-pole RCCBs for single-phase and 4-pole for three-phase systems.

2- Sensitivity: Ranging between 10mA to 500mA, 30mA for human life protection and 300mA for fire protection are standard.

3- Nominal Current Value: The selection should align with the nominal current allowed by preceding thermal magnetic protection.

4- Types:

RCCBs: Cuts circuits in case of ground leakage, necessitating an additional fuse for overload and short-circuit protection.

RCBOs: Integrated miniature fuses eliminate the need for additional fuses.

Earth Leakage Relays (CBR): Suited for industrial use in three-phase systems with high-value currents, cutting circuits during earth leakage occurrences.