Voltimum Tech Talks: Earth Electrodes

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Voltimum Tech Talks: Earth Electrodes

Published: 5 July 2022 · Category: Training related PDFs

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Earth electrodes Tim Benstead CEng; MSC; MIET; MCIBSE; BEd(Hons) What is an earth electrode? Part 2 definition: Conductive part, which may be embedded in the soil or in a specific conductive medium, for example, concrete or coke, in electrical contact with the Earth Purpose • To create a TT earthing system – 411.5.1 • Part of a lightning protection system – BS EN 62305-1 • Foundation earthing – 542.2.3 • To support TN earthing systems – 411.4.2 • Earth generating sets – clause 2 BS 7430 Regulation 411.4.2 – TN systems • New recommendation • Not to make a TN earthing system a TT earthing system • No stated maximum permitted voltage • No stated maximum earth electrode resistance value • A regulation to help limit the touch voltage should there be a loss of the PEN conductor in a PME supply. • 𝑅! = 𝑅" × Limiting touch voltage Load (kW) #! #" $#! 𝑹𝑳 𝛀 𝑹𝑨 𝛀 𝑈# = 50 𝑉 𝑈# = 100 𝑉 11 4.8 1.1 3.1 7 7.6 1.8 4.9 3 17.6 4.3 11.5 Based on Table 14.1 Guidance Note 5 published by the IET BS 7430: 2011+ A1:2015 • Code of practice for protective earthing of electrical installations • provides recommendations and guidance on meeting the requirements for the earthing of electrical installations Maximum values of earth electrode resistance • For independent earth electrodes associated with the local earthing of the star point of generating plant – earth electrode resistance should not exceed 20 Ω. • Additional protection – Note 2 Table 41.5 – as low as practicable and not exceeding 200 Ω to...