Means of detection of arc faults Manufacturers differ in how they choose to conform to the requirements of the Standard. Scolmore applies three characteristics in complex algorithms which, when taken together, will cause its AFDD to trip. These are: ●
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Noise – HF noise in the high kHz to the MHz region. This ‘noise’ is generated by the movement of the arc roots at the cathode. Whilst there are other sources of ‘noise’ which are naturally generated by electrical equipment operating normally, these are of a different nature and the algorithm filters them out. Continuous – ‘noise’ must not be of a brief duration or very intermittent. It is only a continuous process that will lead to the creation of a fire risk and, therefore, where ‘noise’ is intermittent
this will not lead to the operation of the AFDD. ●
Current variation – erratic variations in current and waveform distorting the typical sinusoidal waveform of the normal supply. A series arc will have an impact on the nature of the load current within a final circuit. At the point of arcing there will be an increase in heating with a corresponding variation in current. The AFDD algorithm will sense this changing current.
Unless all three elements are present the AFDD will not operate, as it is unlikely a true series or parallel arc will be present.
Parallel Arc
Conclusion It is well recognised that arcing can, and will, lead to fire. An AFDD provides additional protection against fire and is particularly beneficial when protecting final circuits supplying socket-outlets. BROWSE THE ELUCIAN ONLINE PRODUCT CATALOGUE AT: WWW.RDR.LINK/EAS016