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Light reading

MrJack96
057333447b9d9089180dba9bdabb529b-huge-fc891021-69a1-4a15-a935-213b1a21c0d8.jpgJust doing a bit of light reading can someone explain this to me please.
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    Next, the formula in section 14.5 is derived as follows:
    1. Assume the external source impedance is small compared with load resistances (this is roughly true, otherwise you'd have volt-drop issues).

    • The voltage across the earth electrode is the touch voltage, which can be calculated by Ohm's Law, VT=IbnREE in my illustration, or using GN5, it's UP=IbnRA

    • All we need to do now, is work out what Ibn is. If we assume the supply has a very low earth electrode resistance, we can then simply use Ohm's Law. We have the supply voltage connecting to only two resistors in series - RL and RA. In this case, is RL the resistance of all loads in the installation in parallel. Hence Ibn= UoCmax/(RL+RA)

    • If we put the expression Ibn for back in the expression UP=IbnRA, and rearrange, we get the formula shown on page 98 of GN5.


    Table 14.1 shows that, for different size load connected in the installation, in kW, what the required earth electrode resistance RA would be to achieve a touch voltage UP of either 50 V or 100 V. These are calculated using the formula on page 98.
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    Next, the formula in section 14.5 is derived as follows:
    1. Assume the external source impedance is small compared with load resistances (this is roughly true, otherwise you'd have volt-drop issues).

    • The voltage across the earth electrode is the touch voltage, which can be calculated by Ohm's Law, VT=IbnREE in my illustration, or using GN5, it's UP=IbnRA

    • All we need to do now, is work out what Ibn is. If we assume the supply has a very low earth electrode resistance, we can then simply use Ohm's Law. We have the supply voltage connecting to only two resistors in series - RL and RA. In this case, is RL the resistance of all loads in the installation in parallel. Hence Ibn= UoCmax/(RL+RA)

    • If we put the expression Ibn for back in the expression UP=IbnRA, and rearrange, we get the formula shown on page 98 of GN5.


    Table 14.1 shows that, for different size load connected in the installation, in kW, what the required earth electrode resistance RA would be to achieve a touch voltage UP of either 50 V or 100 V. These are calculated using the formula on page 98.
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