Difference between instrument earthing and electrical earthing?

Instrument Earth is also called as Reference earth. Instrument Earth all individual shields(Screen) and over all shields single or multi pair cable shall be isolated from electrical earthing due to avoiding interference and terminated different bus bar.


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Instrument bus bar will be connected to grounding dispatcher by 25 sqmm green- yellow cable.Grounding dispatcher to earth pit is connected to 70 sqmm green -yellow cable.

Electrical earthing also called as dirty earth or protective earth.It is used to protect the power system,electrical equipment and personnel from electric shock.


should the two Electrical earthing bus bar and Instrument earthing bus bar connected to the same Earthing system of the whole plant?

Could you please tell me the earthing resistance maximum value and sqmm of earth cable of Electrical Earthing?

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No, Electrical Earthing and Instrument Earthing must be different. They have separate earth pits and thus separate bus bars.

The maximum resistance and cable sqmm depends on plant specifications and may change from one plant to another.