Coke breeze should also not be used due to its highly corrosive nature. Columns 2 and 3 relate to most of the British Isles, but column 5 is more specific to marshy flats around river estuaries. Care should be taken to avoid a site where water flows over it e. Other shapes are not covered here. 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. Allowance should be made for the consequent increase in electrode resistance due to changes in moisture content when using measurements made during the installation of a structure. The standard is relevant in the following sectors:
|Date Added:||22 March 2005|
|File Size:||68.24 Mb|
|Operating Systems:||Windows NT/2000/XP/2003/2003/7/8/10 MacOS 10/X|
|Price:||Free* [*Free Regsitration Required]|
This situation is unlikely to arise if the electrode has a resistance sufficiently low to avoid dangerous voltages to earth. By repeating the measurement with increasing values of a, the apparent resistivity involving greater depths may be assessed.
The value of resistance required might not always be amenable to an automatically set value. This may be achieved by making the dimensions in one direction large by comparison to the other two. It includes a number of editorial changes which clarify the meaning of the text and corrects values and symbols. 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.
The resistance to earth of a given electrode depends upon the electrical resistivity of the soil. This is one of the best design reference i have seen. 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.
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. 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. 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.
Who is this standard for? Customers who bought this product also bought BS EN However, onsite resistivity testing should always be carried out prior to carrying out an earth system design and installation.
To design, specify, inspect and periodically test and maintain earthing systems without endangering those who come into contact with them, users need to coee the guidelines and recommendations outlined in this standard.
The basic bs 7430 code of practice for earthing and properties of practce 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. Premium Membership Get access to premium electrical guides, technical articles and much more! It is therefore important to recognize this issue if a long horizontal tape or bare cable is being considered prctice producing a low earth resistanceeven though the impedance will ultimately be limited to a final value see Figure 4.
Therefore any part of an electrode system which is less that 0. The majority of the formulae presented in this section relate to low frequency currents and high frequency examples are not included.
The resistivity found applies to soil earthinb 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. A possible source of such current might be incompatibility with other buried metalworkincluding other types of earth electrode to which foundation metalwork may be bonded.
In the case of contacts between metalwork within concrete or below ground, such as reinforcing bars, this may best be effected by welding. To obtain a low overall resistance the current density should be as low as possible in the medium surrounding the electrode. The finished joint should be covered with a heavy coat of bitumen. Care should be taken to avoid a site where water flows over it e. Second important characteristic of earthing connection is that it MUST be capable of carrying the maximum expected fault current.
This model earthnig more closely aligned to the basic theory behind the electrostatic behaviour of an earthing system component bs 7430 code of practice for earthing, in effect stating more clearly the interactive effect of the value of s which for practical purposes has long been set as being not less than twice the depth of the rod.
Measurements and Calculations Of Earth Electrode Systems (BS ) | EEP
This is lower than some types of soil. This section deals only with a straight run of conductor. This should include the size and shape of the earth conductor, the resistivity of the soil in which it is buried and the connection of the system to it. It should be noted that these types eatthing 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.
A waterlogged location is not essential unless the soil is sand or gravel. The effect of shape on an electrode codd is related to the current density around the particular electrode considered. In particular, continuous earth currents should be given attention. It is also essential to consider the current density at the surface of the earth electrode and the ground potentials in its vicinity.