Fault Loop Impedance Measurement in Low Voltage Network with Residual Current Devices

S Czapp

doi:10.5755/j01.eee.122.6.1833

Abstract

In every low voltage electrical installation initial verification and periodic verification shall be performed. One of the test performed during the verification is fault loop impedance measurement. This measurement enables to verify effectiveness of automatic disconnection of supply which is the most often used means of protection in case of fault. Residual current devices – obligatory in particular circuits – cause the problem in fault loop impedance measurement. They trip out during the measurement and proper verification of the installation is impossible. Detailed analysis of the meters and residual current devices tripping circuits enables to find solution for proper performance of the measurement. The paper concerns the sources of the unwanted tripping of residual current devices during fault loop impedance measurement and indicates solutions for convenient measurement. Ill. 8, bibl. 13 (in English; abstracts in English and Lithuanian).DOI: http://dx.doi.org/10.5755/j01.eee.122.6.1833

Highlights

According to the standard [1] every low voltage electrical installation shall be verified before being put into service by the user and verified periodically in order to check whether the installation and all its equipment are in satisfactory condition for use
The fault loop impedance is measured in circuits with residual current devices (Fig. 1) which are obligatory in selected circuits [4, 5]
Residual current devices cause the problem in fault loop impedance measurement

Summary

Introduction

According to the standard [1] every low voltage electrical installation shall be verified before being put into service by the user and verified periodically in order to check whether the installation and all its equipment are in satisfactory condition for use. The scope of the initial and periodic verification covers fault loop impedance measurement. Value of loop impedance and selected protective devices influence electric shock and overvoltage hazard [2,3,4]. The fault loop impedance is measured in circuits with residual current devices (Fig. 1) which are obligatory in selected circuits [4, 5]. Residual current devices cause the problem in fault loop impedance measurement. They trip out during the measurement because the measurement current IM is the residual current for residual current devices.

PEN IM

Testing of the example meters

Findings

Conclusions