Patent ID: 7265555
Filing Date: 2007-09-04
Classification: G01R

Abstract:
1. A loop impedance meter for testing an A.C. electrical mains supply incorporating a residual current device, the loop impedance meter comprising an electrical control circuit for connecting a load resistance intermittently between the A.C. main supply terminal and the earth terminal to measure the potential difference between those terminals and to provide an indication of the loop impedance of the A.C. main supply from that potential difference; wherein the control circuit comprises an electronic switch in series with the load resistance, and arranged to open and close the electronic switch by applying a plurality of voltage pulses, the width of the voltage pulses is less than a millisecond, thereby causing a series of measurement pulses of different widths to flow through the load resistance; and wherein the control circuit is arranged to process the results of measuring the loop impedance by extrapolating to the effective impedance at the A.C. mains supply frequency.