Types of Earthing used in instrumentation

There are mainly three types of earthing used in instrumentation.

  1. Power earth
  2. Signal / Instrument Earth
  3. IS Earth

Power earth :

Provides ground reference to all power cables. Usual practice to have MAX . Earthing resistance ~ 100 Ohms (There is no harm if it is lower)

Signal / Instrument Earth :

Provides ground reference to all Signal cables (including ICS systems).

Usual practice to have MAX . Earthing resistance ~ 10 Ohms (There is no harm if it is lower)

3) IS Earth (Intrinsically Safe Earth) :

Provide ground reference for all IS signals. MUST NOT EXCEED 1 OHM.

You can have multiple earthing pits of same kind of earth and can be connected in parallel in order to reduce the over all resistance.

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