Earth/ground clamp for measuring earth resistance of electrical installations

Abstract

An earth clamp for testing contact voltage, comprising a measuring circuit formed of a voltage inducing transformer and a current measuring transformer, adapted to be mutually coupled by an earth conductor whose earth impedance is to be measured, a microcontroller to deliver an alternating voltage to the voltage inducing transformer and, in response, to receive a reference voltage generated in the earth conductor and an earth current i+iinduced in the current measuring transformer, the microcontroller being configured to extract an amplitude E of the reference voltage, an amplitude Iand an amplitude Iof the earth current and a phase shift φ between the reference voltage and the loop current iand to calculate the earth impedance Zb at a determined frequency, the microcontroller also computing the contact voltage Uc at said determined frequency by the product of the earth impedance times the amplitude I.