Connection of Instrument Earthing & Electrical Earthing at the end

http://www.eng-tips.com/viewthread.cfm?qid=142946&page=16

ALso Yogokawa and several other instrument companies recommend separate earth terminals (most likely to avoid the spike of the earth electrode voltage creeping back to instrument) - remember, though the earth resistance must be low (less than 1 ohm), still the high voltage may create a spike of quite a few voltage before the protection shuts it off.

• Feasible? Yes.
• Desirable? Yes.
• Technically correct? Yes.
• A requirement? No.

Thanx for your reply.

But I think I felt a little bit short to ask the right thing.

I'ld like to ask is it right or correct to combine both seperate Instrument Earth & Electrical Earth in any of the earth pits. (Both shorted either in Instrument Earth or Electrical Earth).

Let me explain precisely

1) Seperate Instrument Earth

2) Seperate Electrical Earth

3) Both Earthings are combined or shorted with each other in the Earth pits with a piece of cable grounded in both Instrument & Electrical Earths.

This really may not be a problem (this is the previous guest- that has said no and then provided the link)

The point is that we do not want the spike to travel back, whose magnitude depends on the fault level in the power line.

However since your connection between the electrodes is within pit, this problem is not likely to occur.

However in case of sensitive instruments, just contact the manufacturer, since we don't want the guarantee to be nullified due to these minor things.

In fact, it must be what you have said. (i.e.) Seperate Instrument Earth, Seperate Plant Earth and LINK both at the earth level. This is what is recommended strongly in IEEE 1100 too.

Can be done..but take care that there is no more than one panel earthing leads going to the grid causing a loop in case of big spike it can pass a current through the panel thru those earth points connected at diffenerent points having different voltage levels on fault.