Loop Impedance is the measurement used to describe the restriction of current though the "loop" that would be caused by a fault. Lesser the resistance more will be the current flowing through the circuit thus ensuring faster fault isolation. Loop Impedance Test is generally conducted at power points to ensure loop impedance value is under permissible limit.


Loop impedance testing, also known as loop resistance testing or simply loop testing, is an important procedure conducted in electrical installations to assess the health and safety of the electrical circuits. This testing method is primarily used to measure the impedance or resistance of the electrical circuit's loop, which consists of the phase conductor, neutral conductor, and protective conductor (earth).

The loop impedance of an electrical circuit plays a crucial role in protecting against faults, such as short circuits and overcurrents. It determines the effectiveness of the protective devices, such as circuit breakers and fuses, in quickly interrupting the circuit when a fault occurs. By measuring the loop impedance, electrical professionals can evaluate the performance and efficiency of the protective devices and identify potential faults or hazards in the circuit.

The process of loop impedance testing involves the use of specialized instruments called loop impedance testers or loop testers. These testers are designed to inject a test current into the circuit and measure the resulting voltage drop across the loop. The ratio of the voltage drop to the injected current gives the loop impedance value, which is typically expressed in ohms.

During the testing process, all protective devices, such as circuit breakers, residual current devices (RCDs), and fuses, should be in their normal operating position. The tester is connected to the circuit, and a test current is applied. The tester then measures the voltage drop across the loop, which is used to calculate the loop impedance.

Loop impedance testing serves several important purposes:

  • Fault identification: By measuring the loop impedance, electrical professionals can identify potential faults in the circuit, such as high resistance connections, damaged conductors, or faulty protective devices. These faults can compromise the safety and performance of the electrical installation, and timely detection allows for necessary repairs or replacements.

  • Compliance with regulations: Loop impedance testing is often required to ensure compliance with electrical safety regulations and standards. Many countries have specific regulations in place that mandate regular testing of electrical installations to ensure their safety and reliability.

  • Preventing electrical hazards: Loop impedance testing helps in preventing electrical hazards by verifying the effectiveness of the protective devices. If the loop impedance is too high, it may indicate that the protective devices will not operate efficiently during a fault, potentially leading to electrical fires or electric shock hazards.

  • Troubleshooting: When there are issues or malfunctions in an electrical circuit, loop impedance testing can be a valuable diagnostic tool. It allows electricians to pinpoint the location and nature of the problem, aiding in the troubleshooting process and facilitating efficient repairs.

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