Megger Instruments Limited

Jeffrey Jones

Stanislaw Zurek

Mark Hadley

Freddie Chin

Loop resistance is measured in a live-earth conductor loop comprising a residual current device powered by an alternating current mains supply. A measurement circuit having a low-pass filter characteristic arranged to substantially remove signal components at the frequency of the alternating current mains supply is used to measure, in a first period, a voltage across live and earth conductors of the live-earth conductor loop to determine a first voltage. A current application circuit is used to apply a unipolar test current having a magnitude below a trip current value of the residual current device for a second period and the measurement circuit is used to measure a second voltage between the live and earth conductors. Based on a difference in test current between the first and second periods and a difference in voltage between the first voltage and the second voltage, the resistance of the live-earth conductor loop is calculated.

Measuring loop resistance

In a meter for performing a measurement of an electrical parameter, an output from a sensor is sampled to produce at least one sample, and an iterative method is performed comprising: producing further samples; holding in memory a stored array of samples comprising the at least one sample and each of the further samples from each iteration; determining a measure of statistical variability of a mean for the respective iteration from a measure of statistical variability and from the number of samples used to generate the measure of statistical variability; comparing the measure of statistical variability of the mean with a pre-determined threshold; and generating an electrical signal indicating a state of the measurement if the measure of statistical variability of the mean of the samples taken during the measurement is less than or equal to the pre-determined threshold.

Meter for measuring an electrical parameter

An electrical plug for testing an electrical mains socket is provided. The plug comprises a pin for engagement with a pin receptor of the mains socket. The pin comprises first and second electrical contacts, each comprising a surface portion to engage with a different respective region of the receptor. The first and second contacts are electrically isolated from one another at the pin. An electrical testing system and a method of testing an electrical mains socket is provided. The testing system comprises the electrical plug and a first circuit connected to the contacts and configured to measure an electrical resistance therebetween. The method includes providing the electrical plug and measuring an electrical resistance between the electrical contacts. A further method is provided for testing an electrical mains plug comprising a pin, by providing an electrical socket with a pin receptor having first and second regions electrically isolated from one another.

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Dover, United Kingdom

Jeffrey Jones