Risk assessment and control in protection against indirect contacts for Medium Voltage earth faults in open-cast mines and quarries

Open-cast mines and quarries often use high power electrical machinery to extract materials from the site they are located. Due to the power of machinery, these activities require a MV electricity supply. They are very often located in sites where the soil has high resistivity, and it couldn’t be easy to guarantee the protection against indirect contacts according to EN 50522:2010-11 provisions. This is particularly true along the excavation front. The electrical properties of the soil on which the machinery are installed may change quickly and so changes the distribution of the potentials during MV earth faults. Risk control based on touch voltages measurements could not be a reliable technique; better to search structural solutions to guarantee the worker’s protection. The requirements of the EN 50522:2010-11 standard are evaluated not only under the electrical point of view, but keeping in mind the particular context. A metal mesh laid along the operating locations and connected to the metal chassis of the machinery is a simple and reliable solution. Measures executed in Italian quarries confirm this.