EARTHING/GROUNDING SYSTEMS, AN OVERVIEW
Soil resistivity testing The first stage of any earth system design is the undertaking of a comprehensive soil resistivity survey to determine themake up of the soil and acidity levels. Fromthe data produced a soilmodel will be generated to assist in determining the optimum location and depth of the electrode system. An initial research phase is required to gather information about nearby metallic structures, is there geological survey data available? If so obtain it and use it as comparative data when your soil survey is processed into a soil model. Carry out a CAT scan of the area of the test to ensure there are no electrical cables that can distort or be damagedwhen the test probes are driven into the ground. Prior to commencement of testing ensure the test instrument is set up adequately i.e. power levels, frequency, interference and filtering. As earthing systems are installed near the surface of the earth, the top soil layers being subject to higher current densities are themost significant and require themost accurate modelling. Soil resistivity can vary significantly both with depth, and from one point to another at the site, and as such, a single soil resistivity measurement is usually not sufficient. Taking a number ofmeasurements along a line using different spike separations,will provide an indication of howthe soil resistivity varies with depth, whilst taking measurements along different lines will indicate howthe resistivity changes across the site or alternatively if possible at a 90° tangent.
Aneffective earthsystemhas anumberofdefiningcharacteristics: • Low impedance ground (low resistance, low inductance, high capacitance) • Ability to disperse full potential fault current levels • Ability to withstand repeated faults • High energy dissipation to requisite levels • Proper orientation • Corrosion resistance • Theft resistant • Low touch and step potentials • Minimal bends in conductor system(eliminate 90° bends if at all possible) • Maximise bend radius wherever bends occur • Earth potential rise is within acceptable limits • Transfer potentials are within acceptable limits
• A functional lifespan of approx. 30 years providing that the facility load or structure is not amended, whereupon a redesign of earthing system will be necessary.
Common improvement strategies: • Increase electrode surface area • Use a capacitive enhancement product • Increase conductor size • Decrease the number of connections • Lower inductance • Increase capacitance
• Electrodes must be spaced appropriately for maximum effect. They should ideally be equally spaced to their depth; for example a 10 meter deep rod should be 10meters away fromthe next earth rod.
Ground improving products for
earthing systems A number of products have been developed over the years to improve earthing arrangements. Some products have suffered with idiosyncratic problems, including:
• Substantial corrosion of copper elements; some materials available in the market can corrodemetallic components until they are completely destroyed.
• Unreliability and unpredictability of material behaviour after installation: problems such as expansion post-installation resulting in distorted surface level profile, causing trip hazards and requiring remedial action.
• Ease of extraction and theft of copper earthing/grounding elements: theft of valuablemetallic components has plagued the industry.
• Environmental pollution; Leeching away of earthing/grounding improvement compound: this problemhas faced a number of products,where during and subsequent to installation it has leaked away into fractures in the surrounding groundmass.
FM Sudafix is committed to possessing the best product range in the sector and backfill earthing improvement materials are no exception. With the evidence provided by independent testing it is the opinion of FMSudafix that Conducrete® is the best product to support earthing projects. Designed to a demanding specification Conducrete® possesses impressive attributes to enhance earthing systems.
Formore information onConducrete® please refer to the relevant product page +44 (0)115 975 7600
www.fmsudafix.com 11
EARTHING
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