MV&LV Earthing Calculation Study for KAIA Project Load Centre A (BS 7430)
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Contents
A. Purpose/Scope ...................................................................................................................................... 3
B. Earth electrode rods: ............................................................................................................................ 4
C. Earth round conductor electrode: ...................................................................................................... 10
D. Earth rod with round conductor electrodes combination earthing network: .................................... 11
E. Interconnection of MV and LV Earths ................................................................................................. 12
F. Calculation of Touch and Step Potentials ........................................................................................... 14
G. Allowable touch and step potentials .................................................................................................. 15
H. Current Density at Surface of Earth Electrode .................................................................................... 16
I. Appendices : ........................................................................................................................................ 19
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A. Purpose/Scope
The purpose of this report to obtain the MV&LV earthing calculation study
for load centre A of KAIA project according to BS Code books
(BS 7430:1998), (BS 7354:1990) and the design report.
All the formulas and tables are copied from BS 7430:1998 and
BS 7354:1990
This study is to be used to aid in specifying the following:
• Earth electrode rod length.
• Number of earth electrode rods per each loop.
• Length of Earth round conductor electrode.
• Resistance of MV earthing network.
• Resistance of LV earthing network.
• Combined earth resistance interconnection of the MV and LV
networks.
• Touch and Step Potentials.
• Current Density at Surface of Earth Electrode.
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B. Earth electrode rods:
The resistance to earth of a rod or pipe electrode R, in ohms, is given by
the following equation:
Load Centre A - Structural floor level is 7m above MSL with the design
water table level at 4m above MSL, this level is based on recommendations
of HUTA and is subject to final confirmation by them.
So the effective length of the electrode rod through the wet soil (10 ohm.m
resistivity) will be [(3*2.4)-(7-4)] =4.2 m, where the total length of electrode
rod 3*2.4 = 7.2 m.
L = Effective Length of the electrode exist in the wet soil = 4.2 m
d =Diameter of the earthing rod = 0.02 m
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ρ = wet Soil resistivity (according to the design report) = 10 ohm.m
Then, R = 2.486 ohm for one earthing rod.
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