Earthing Conductor

Hello,

Presuming that you are domestic to the US of A, the NFPA is responsible for the National fire codes in the United States, including NFPA 780 – Standard for the Installation of Lightning Protection Systems. For almost any application, anywhere, this is about the best standard out there.

Rem: "Any sufficiently advanced technology is indistinguishable from magic." RAH

Thanks GLB, but still I realy need a formula that helps defining the size of grounding and Lightning cable, By the way I need it for a project in Saudi Arabia

I have an Excel spreadsheet that I put together based on BS 7430 1991 that may help (you would need a copy of this for ref to constants). As a rule of thumb, 70mm2 bare cable for underground earth mat & 25mm x 3mm for any of the copper tape. The depth of the conductor does not have the same impact on earthing as the soil resistivity, in Saudi this may be high & "enhancing compounds" could be required.

Can you post this excel spread sheet

Im in the USA and would like to see the differences between British and USA standards

Would you please post this excel spread sheet, or you can send it to my email rabea@uni-groups.com, thanks in advance

Dear Rabea,

To design the earthing system is not simple as determining the conductor size and the depth of the rod embeded. But it is a complex design involving the resistivity of soil, the change of weather and humidity, the designed fault level, the power system, the earthing system (TT, TNS, TNC, etc), the purpose of protection (LV, MV, or IT), Calculation of earth resistance, the earthing system (Vertical Rod, Grid/Mesh, Ring ground, Radials, etc.), etc.

But your 1st question can be answered :

For Earth Electrode and Earth Conductors ;

A= I_F x √t_F / K, where ; A = Cross sectional area of conductor/rod(mm²), I_F = fault current (Amps), t_F = duration of fault current (seconds), K = material coefficient

For protective conductor, PEN conductors, and equipotential bonding conductors ;

S =√I²t / K, S = cross section, I = rms fault current (A), t = disconnection time of protection device, K = material coefficient.

But for your 2nd questions has no definite reference as I wrote above.

regards,

Abu Khansa