What is the difference between instrument earthing and normal earthing? and why

What is the difference between instrument earthing and normal earthing? and why is it necessary to do so?

Question Posted / shashank s

3 Answers
29730 Views
Atul, I also Faced
E-Mail Answers

Answers were Sorted based on User's Feedback

What is the difference between instrument earthing and normal earthing? and why is it necessary to d..

Answer / mugil

Instrument Earth:
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.
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 Earth:
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.

Is This Answer Correct ?

17 Yes

3 No

What is the difference between instrument earthing and normal earthing? and why is it necessary to d..

Answer / jigaranadkat

Dear Shashank,

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.

Is This Answer Correct ?

13 Yes

9 No

What is the difference between instrument earthing and normal earthing? and why is it necessary to d..

Answer / elam

How long distance need to plant earth to instrument earth

Is This Answer Correct ?

4 Yes

1 No

Post New Answer

More Instrumentation Interview Questions

Q1]IF THE RANGE FOR FLOW IS -35 TO 125 WHAT WILL BE THE SPAN FOR ABSOLUTE AND FOR NORMAL? Q2]HOW TO CALIBRATE CAPILLARY TYPE LT? Q3]HOW MANY ERROR CALCULATIONS ARE THERE USED IN PROCESS INDUSTRIES? Q4]HOW TO CALIBRATE TEMPERATURE TRANSMITTER? Q5] HOW TO CALIBRATE LEVEL TROLL AND HOW TO CONNECT? Q6]PLEASE TELL ME THE BASIC FOR INSTRUMENTATION WHICH IS APPLIED FOR CALIBRATION AND FOR ALL? PLEASE MAIL THE ANSWER TO honest_yes@yahoo.in

0 Answers Cegelec, Honeywell,

A pressure Tx accuracy is 0.2%. Signal o/p is 4-20ma.span is 16 Ma.how many deviate the o/p then calibration needed

1 Answers

What is mean by SMART in an Instrumentation. is any full form for SMART?

3 Answers

What is loop or pigtail in an impulse line?

8 Answers Qatar Airlines, Qatar Petroleums,

why we cant transmit the dc current easily

1 Answers

why we set -10 volt in vibration sensor output,why not +10 volt

3 Answers Sabic, TVS,

Absolute pressure is 700psi,what will be the gauge pressure?

1 Answers IFFCO,

What is the working principle of Dozing valve used in cement industry?

1 Answers

when an eddy current probe is installed inside of a turbine or compressor in case of probe problem same as:crash of head of probe,changing the scale factor because of low measuring gap(physical gap is ok(example=1.14mm)but voltage is reduced(example=-6 volts),is any way to check the probe,when the ohm of probe is ok.thank you,(Karim Tavakoli)

1 Answers

What is surge and how is it prevented, what is the purpose of bypass valve across AS valve.

0 Answers ADMA OPCO,

What does a hookup diagram look like? can you give sample drawing. thanks.

1 Answers

If any control valve create hunting problem, what is the possible reason and solution?

6 Answers

For more Instrumentation Interview Questions Click Here