Bs 7430 code of practice for earthing

If possible, it is advantageous and recommended to measure the resistance of several such footings to gain an indication of the likely variation of resistance. Most first approximation formulae are related to homogenous soil, which is rarely the case in practice, where the different layers of strata will affect the distribution of current passing through the electrode. It may be considered necessary to apply numerical methods which are more complex than the formulae given below and software is available to carry out the more detailed calculations. The products of corrosion occupy a greater volume than the original metal and cracking might occur. The resistance to earth of concrete encased steelwork or of concrete reinforcing bars varies according to the type of soil, its moisture content, and the design of the foundation.

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BS 7430:2011+A1:2015

This applies particularly to surfaces which might have been primed before assembly. Alternating current should not be expected to cause corrosion, but, rectification sufficient to produce a very small proportion of direct current might take place. The resistivity found applies to soil depth a, so by repeating the measurement with different values of athe average resistivity to various depths may practie found and the results pracyice whether any advantage is to be gained by installing deeply driven electrodes in order to reach strata of a lower resistivity.

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Measurements and Calculations Of Earth Electrode Systems (BS ) | EEP

Coke breeze should also not be used due to its highly corrosive nature. Manish Darji Feb 26, Overview Product Details What is this standard about?

Premium Membership Premium membership gives you an access to specialized technical articles and extra premium content electrical guides and software. Where the structure is supported on many similar footings, it may be considered feasible and more satisfactory to measure the resistance of one footing before it is electrically connected to othersand before there are any other electrically paralleled footings close by.

There are commercially available materials to achieve this effectively, but care should be taken to understand how they work during installation to ensure xode they remain in contact with the rod or strip and do not shrink or swell away after drying out. We use cookies to make our website easier to use and to better understand your needs. Therefore any part of an electrode system which is less that 0. It is important to ensure that their resistance areas do not overlap.

Thus a pipe rod or strip has a much lower resistance than a plate of equal surface area. This website is best viewed with browser version of up to Microsoft Internet Explorer 8 or Firefox 3.

It includes a number of editorial changes which clarify the meaning of the text and corrects values and symbols.

When two or more strips in straight lengths, eagthing of length L in meters m and a separation distance s metres are laid parallel to each other and connected together at one end only the combined resistance may be calculated from the following equation:. After construction and with the passage of time this moisture content will approach equilibrium with that of the soil, and will usually be dryer than when first laid.

This may be taken as an indication of the possible gain from driving deeper rods, etc. It covers earthing cod design parameters for structures, electrical equipment and systems.

Accept and continue Learn more about the cookies we use and how to change your settings. The products of corrosion occupy a greater volume than the original metal and cracking might occur. Please download Chrome or Firefox or view our browser tips. Find Similar Items This product falls into the following categories. You may find similar items within these categories by selecting from the choices below:. The total electrode area formed by the underground metalwork of large structure may often be used to provide an earth resistance lower then that obtainable by other methods.

To obtain a low overall resistance the current density should be as low as possible in the medium surrounding the electrode. Your basket is empty. The finished joint should be covered with a heavy coat of bitumen. It should be noted that environmental conditions such as temperature have an impact on earth resistivity with a corresponding decrease in resistivity as temperature rises. Other shapes are not covered here.

BS +A Code of practice for protective earthing of electrical installations

The resistivity cose determined applies to an electrode separation distance a, which is related to the depth of pracgice. If possible, it is advantageous and recommended to measure the resistance of several such footings to gain an indication of the likely variation of resistance. Measurements of the soil resistivity for the pre-determination of the resistance to earth or the impedance to earth should be carried out using a four probe method widely known as the Wenner method as follows.

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