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صفحه اصلی سایت Technical Information Power And Control Cables Power Appendixes Guide to the Wiring Regulations Inspection, Testing and Certifcation ; Earth fault loop impedance (ELI) testing

صفحه Inspection, Testing and Certifcation ; Earth fault loop impedance (ELI) testing

Inspection, Testing and Certifcation ; Earth fault loop impedance (ELI) testing
Earth fault loop impedance is required to be checked at various places throughout the installation, and generally at every point where a protective device is installed.
For fnal circuits, there are two alternative methods of determining the earth fault loop impedance:
1- Direct measurement of total ELI.
2- Measurement of the circuit Rl + value and addition to the ZDB (earth fault loop impedance at the local distribution board).
External earth fault loop impedance (Ze) :
Measurement of external ELI is necessary in LV supplies to confrm the supply earth condition. External ELI is measured live at the intake position, or close to it, with the means of earthing disconnected from the installation and the loop tester connected to it . The supply to the installation will need to be isolated.
Above Figure is a typical arrangement; in this case for a TN-C-S PME supply .
Testing for total earth fault loop impedance (Zs) :
earth fault loop impedance may be required at various points throughout the installation and will generally need to be measured at every level of protective device.
For confrmation of fnal circuit disconnection times where RCDs are not installed, measured total earth fault loop impedance is usually required for all circuits.
Zs may be carried out by direct measurement at the extremity of a circuit.
The physical measurement of ELI is generally as shown in above Figure , and it should be remembered that RCDs in circuit will trip unless the test instrument has a facility to block unwanted tripping. Some ELI testers can test at such small current levels that they are below the threshold of tripping. Alternatively, the RCD must be linked-out of the circuit.