Earth Leakage Circuit Breaker (ELCB) Sizing Guide

ELCB sizing is crucial to ensure proper protection of electrical circuits and personnel from electrical faults and leakage currents. When sizing an ELCB, you should consider several factors such as the load current, the required sensitivity, and the type of ELCB to use. Here's a step-by-step guide on how to size an ELCB:

Determine the load current:

Calculate the total load current of the circuit you want to protect. This can be done by adding the currents of all connected devices and appliances. The load current will help you choose an ELCB with the appropriate current rating.

Choose the type of ELCB:

There are two types of ELCBs – voltage-operated and current-operated. Voltage-operated ELCBs (VOELCBs) are suitable for installations with TT earthing systems, while current-operated ELCBs (RCCBs/RCDs) are recommended for TN and IT earthing systems.

Select the sensitivity:

The sensitivity of an ELCB is the amount of leakage current that will cause the device to trip. For domestic and general-purpose installations, a sensitivity of 30mA is recommended to provide sufficient protection against electric shock. For higher-risk environments or applications, such as industrial or agricultural installations, a higher sensitivity (e.g., 10mA or even lower) may be required.

Determine the ELCB's breaking capacity:

The breaking capacity of an ELCB is its ability to interrupt a fault current without damage. Choose an ELCB with a breaking capacity that is equal to or higher than the prospective short-circuit current at the point of installation.

Choose the appropriate tripping characteristics:

Select the tripping characteristics that best match the application. Type AC ELCBs are suitable for circuits with mainly resistive and inductive loads, while Type A ELCBs are used for circuits with pulsating DC residual currents (e.g., circuits with single-phase rectifiers). Type B ELCBs are used for circuits with smooth DC residual currents, such as those found in electric vehicle charging stations.

Verify the ELCB's compliance with relevant standards:

Ensure that the ELCB you select complies with the applicable standards and regulations in your country or region, such as IEC/EN 61008 or IEC/EN 61009 for RCCBs and RCBOs.