What Is Loop Impedance (Earth Fault Loop Impedance) Measurement?

Regular and accurate measurements are of great importance for the continuity and sustainability of electrical facilities. One of these measurements is Loop Impedance measurement. Loop impedance is required for electrical installation conformity reports.

You May Be Interested In: Electrical Installation Conformity Report

What is Loop Impedance?

Loop impedance can be defined as the source impedance measured between the Line (L) and Protective Earth (PE). If an electrical installation is protected by overcurrent protection devices, the loop impedance must be measured. The impedance value between the phase and the PEN conductor must be within the standards for the protection element used to open the circuit within the desired time interval due to the fault current occurring during any short circuit.

How is the Measurement Performed?

The device takes a certain current from the phase line and transmits it to the ground via the ground line. This current flowing through the ground (zero point) returns to the phase conductor from the transformer star point grounding (operational grounding), that is, it returns to the device. The sum of the resistance values of all lines it passes through in this direction is called loop impedance. This impedance value includes the following values:

• Protective grounding
• Operational grounding (System earthing)
• Transformer secondary winding resistances
• Phase conductor resistance
• Protective grounding conductor resistance

You May Be Interested In: Grounding Measurement

The sum of these five is the loop impedance. The grounding value measured in this way is the correct one. Because protection elements react to the short circuit current that will occur on this line. For example, in a TT system, in case of a short circuit from the phase line to a machine body, these five items are the path the current will follow.

Connecting the device for loop impedance measurement