resistance to earth of a plate R in ohms (code of practice earthing history First published as CP First published as BS BS Code of practice for protective earthing of electrical installations. 16/22 Total Solution to Earthing & Lightning Protection | 9AKKA Technical BS Code of practice for protective earthing of electrical.
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The purpose of earthing System earthing involves the provision of a connection to the general mass of earth. Overview Product Details What is this standard about? Columns 2 and 3 relate to most of the British Isles, but column 5 eearthing more bbs7430 to marshy flats around river estuaries.
In high resistivity locations or on rocky ground where long term performance is required, it may be considered necessary to utilize a conductive concrete to improve earth contact resistance around an earth rod or strip tape where applicable. It is therefore important to recognize this issue if a long horizontal tape or bare cable is being considered for producing a low earth resistanceeven though the impedance will ultimately be limited ezrthing a final value see Figure 4.
Melvin Surita Mar 07, A waterlogged location is not essential unless the soil is sand or gravel. Chemical treatment of soil has environmental implications and should not be considered as a long term solution in order to meet a specified level of resistance, apart from the risk of corrosion to the earthling system. Soil resistivity may be measured in a similar manner to the establishment of the resistance of the earth electrode.
Wherever significant continuous earth leakage current is expected, it is recommended that a main electrode of the types described in previous section be provided to which the foundation electrodes can be bonded to provide auxiliary electrodes, thus giving assistance to high fault currents.
Table 1 gives examples of resistivity only. This requires careful assembly during installation to ensure that the bottom of the plate is resting in the medium used and not on the chalk or high resistivity substrata.
The value of resistance required might not always be amenable to an automatically set value. It is of particular relevance to: In particular, continuous earth currents should be given attention.
To obtain a low overall resistance the current density should be as low as possible in the medium surrounding the electrode.
BS +A Code of practice for protective earthing of electrical installations
peactice The resistivity found applies to soil depth a, so by repeating the measurement with different values of athe average resistivity to various depths may be found and the results indicates whether any advantage is to be gained by installing deeply driven electrodes in order to reach strata of a lower resistivity.
The effective resistivity is also controlled by the mineral salts in the ground and the level of moisture contentwhich is why it should be remembered that readings taken long after installation can vary considerably from the original test results. This website is best viewed with browser version of up to Microsoft Internet Explorer 8 or Firefox 3.
It eagthing includes some technical changes to correct and clarify formulae and equations. Earthing systems should consist of copper conductors, copper clad or austenitic steel rods of appropriate dimensions, cast iron plates, or steel piles used individually or connected together in combination to form a single local earth electrode system.
This situation is unlikely to arise if the electrode has a resistance sufficiently low to avoid dangerous voltages to earth.
It is important that consideration is given to the possibility of corrosion of the metalwork reinforcement. It should be noted that these types of measurement are not always simple and can often result in a wide range of resistance values depending upon a number of factors such as those mentioned in above paragraph.
The connecting strip to the above ground disconnection point should be fully insulated to avoid electrolytic action.
Measurements and Calculations Of Earth Electrode Systems (BS ) | EEP
Premium Membership Get access to premium electrical guides, technical articles and much more! Find Similar Items This product falls into the following categories. There are commercially available materials to achieve this effectively, but care should be taken to understand how they work during installation to ensure that they remain in contact with the rod or strip and do not shrink or swell away after drying out.
Care should be taken to avoid a site where water flows over it e. Please download Chrome or Firefox or view our browser tips.
Current should be passed between the two outer electrodes and the resistance R may be found as the ratio of the voltage between the inside electrodes to the current conducted through the outside electrodes. This connection should have a resistance not greater than that required to operate safety mechanisms to isolate the electricity supply from a fault situation. There are many configurations that can be set out under this heading, but a few of those which one is most likely to try foe in order to achieve the required value are included especially when bs4730 with deep reinforced piles, etc.
Ideally confirmation of the combined resistance of all the electrodes should be obtained, but the earth resistance of a structure covering a large area might be quite low and an accurate measurement on a completed structure might be difficult or impossible to achieve.
The effect of shape on an electrode resistance is related to the current density around the particular electrode considered. An earthing system should be of the highest integrity and of robust construction to ensure that it remains bs7340 and will not endanger the ;ractice and safety of persons or their surroundings.
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.
When two or more strips in straight lengths, each of length L in meters m and a separation distance s metres eaething laid parallel to each other and connected together at one end only the combined resistance may be calculated from the following equation:. Dry sand, gravel, chalk, limestone, whinstone, granite, any very stony ground, and all locations where virgin rock is very close to the surface should be avoided if possible. Manish Darji Feb 26, The basic nature and properties of soil in a given location cannot be changed without considerable expense, and careful consideration of the geology should be used to determine the best location for an earthing system.
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.
Other shapes are not covered here.