Technical Articles
The primary risk associated with operating electrical appliances is the possibility of electric shock. While such shocks are to be often momentary, they can be extremely hazardous.
Two main causes of electric shock are short circuits and leakage currents. Short circuits are generally well-known, and protective devices such as MCCBs, MCBs, and ACBs are commonly installed to address this issue.
On the other hand, earth leakage occurs due to factors such as equipment wear and tear or moisture around terminals, which can cause partial breakdown of insulation between the power supply and the earth. Earth leakage currents are particularly dangerous as they can lead to cable overheating and insulation failure, potentially resulting in significant property damage and even loss of life.
A body resistance model would indicate approximately 1,000 Ω from hand to hand, or about 1,100 Ω from hand to foot. It is believed that the greatest number of injurious shocks involve a current pathway that is either hand to hand or hand to feet, because the vital parts such as heart and lungs encounter the flow of current.
In Image shown, leakage current beyond 30mA can be more severe and leading to death. 30mA sensitivity is required for protection in domestic installations where the person may come in direct contact with electric equipment like machine tools, motors, EV charging stations, machine control panels, power control panels, etc.
An earth fault occurs when a conductor carrying current comes into direct contact with the ground due to insulation fault or open circuit condition. On the other hand, earth leakage happens when the current in the system finds an alternative path, other than the active and neutral conductors. Understanding these differences is crucial for maintaining electrical system safety and efficiency. Therefore, earth leakage relays require higher sensitivity and are used in scenarios where human contact is possible. In contrast, Earth Fault Relays are generally employed to safeguard installations by detecting insulation failures that could lead to fires.
An earth fault occurs when a conductor carrying current comes into direct contact with the ground due to insulation fault or open circuit condition. On the other hand, earth leakage happens when the current in the system finds an alternative path, other than the active and neutral conductors. Understanding these differences is crucial for maintaining electrical system safety and efficiency. Therefore, earth leakage relays require higher sensitivity and are used in scenarios where human contact is possible. In contrast, Earth Fault Relays are generally employed to safeguard installations by detecting insulation failures that could lead to fires.
The Earth Leakage Relay (ELR) is a microcontroller-based device designed to detect low-level leakage current and isolate faulty circuits from the system. It utilizes a Core Balanced Current Transformer (CBCT) that employs residual magnetic flux technology to sense leakage current. The vector sum of all currents passing through the CBCT should be zero.
Īr + Īy + Īb= 0 For 3 phase 3 wire system
Īr + Īy + Īb + Īn =0 For 3 phase 4 wire system
The CT wires should be placed adequately away from high current carrying conductors or source of strong magnetic field to avoid noise pickup.
Rajesh R Shirodkar,
DGM-Corporate CommunicationRajesh Shirodkar is a seasoned marketing and business leader with over 20 years of experience in the automation and electrical industry, spanning marketing communications, sales, business development, and software solution selling. He has led successful brand transformation initiatives and high-impact marketing programs, including branding and account-based marketing campaigns, as well as industry events that drive visibility, engagement, and growth. With expertise in brand building, lead generation, solution selling, and sales enablement, Rajesh is known for translating technology and business offerings into compelling value propositions and delivering sustainable growth through strong stakeholder collaboration.
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