Can we connect both Elec. & Inst. Earthing system in same grid.

Earth is earth is earth.

• It is better, though not a requirement, to keep power earths and instrumentation earth wiring separate until the last connection onto the earth electrode system. The reason is that, if combined, the voltage drop along the combined earth conductor can, under power fault conditions, put a voltage onto the instrument earth system and that can have some peculiar effects on all the instrumentation. "Can", not "will", as these days most instruments are so bomb-proof that the effects are usually minimal.

Follow the specification "they" have provided.

Correct and GA,

BTW all instruments are not bombproof and we had quite a few computers damaged.

Never and ever combined both Instrument Earth with Electrical Earth system togeather. In my previous company, I have problem with the PLC card for the instrument burnt. Finally, when I make a study on the erathing system, I found that the electrical earthing system and the Instrument Earthing system was combine togeather.

What happen is that, during the maintenance days, there will be some welding works in the area by the mechanical people and the problem with "them" (these peolpe) is they don't even care about they welding set earthing. They will earth their welding set any place convenion to them and start the welding works at any place they like.

At the end, the return high current from the point of welding, will flow every where and these current will find the lowest resistence path to flow back to their welding set. If your instrument is earth together with the electrical earth, I will sure that your instrument will burnt by the welding current.

At the end, I have seperate all the instrument earth with the electrical earth and burried a 1.2 meter x 1.2 meter x 10 mm thick copper plate for the instrument earth. Since then we don't have these problem with the instrument spoil or PLC card burnt.