Earthing Guidelines

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Earthing RecommendationsFor Programmable Controller Systems

ES30001 (Part-I)

ES30001 Part-I (Rev.-2) JULY 2001


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Contents

1. Scope.........................................................................................................................................5

2. Definitions...............................................................................................................................5

3. Function of Plant Earth........................................................................................................5

4. Function of Primary Earth.....................................................................................................6

5. Function of Secondary Earth.................................................................................................9

6. Earthing of Multiple panels.................................................................................................12

7. Earthing of Panels with Multiple Power feeds..................................................................14

8. Earthing of Remote Stations...............................................................................................14

9. Connecting MMI, Peripherals..............................................................................................14

10. Cables and Conduits ............................................................................................................15

11. Verification of Earth Connections......................................................................................15

12. Earth pit.................................................................................................................................17

13. Summary................................................................................................................................18

Notes......................................................................................................................................19


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Disclaimer

"Larsen&Toubro Limited, its affiliates and employees disclaimall liabilities & warranties (includinglost

profits or any other incidental damages) for accuracy, currency, completeness of theinformation contained

herein

In linewith thecompanys policy of continuous development. Theinformation contained in this document is

subject to changewithout prior notice.

Selection of materials and/ or equipment is at thesolerisk of theuser of this publication.

Thecontents of this document areproperty of Larsen&Toubro Limited. No part of this document may be

copied, distributed, transcribed, or translated into any formor by any means, or disclosed to any third party

without theexpress written permission of Larsen&Toubro Limited."

Document Information

Document #: ES30001-Part-I

Revision: 2

Release date: July 2001

Credits

Technical team: Revised by (Rev. -2)

Omkar Saroop R.K.Pandagare

Sujit Dey R.M.Karlekar

A A Samson


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1. Scope

The Part 1 recommendations apply primarily to the Programmable Logic Controller (PLC), their

Remote Stations and associated peripherals, such as MMIs and are primarily for addressing

Electromagnetic interference and Electromagnetic compatibility (EMI/ EMC)

Part 1 does not address the Drives and their interconnections with the PLC systems.

2. Definitions

2.1 Panel: The metal enclosure in which the PLC and the associated equipment are

mounted and housed.

2.2 PLC System: Comprises of the Power supply Units, CPU, I/ Os, Mountbases.

Communication Interfaces &remote stations.

2.3 Primary Earth: The earth connected to the Panel.

2.4 Secondary Earth: The earth connected to the PLC system.

2.5 Plant Earth: The earth to which the lightning conductor, earth conductors of other

equipment in the Plant are connected. (E.g. MCC , PCC, H.T Switchgear)

2.6 Equipotential Ground Plane : Ground plane exhibiting zero potential difference

between any two points on it. It does not matter what the absolute potential of the

ground plane to the earth may be at.

2.7 Cable Shield: The metal braid cover on the cables carrying communication signals and

instrumentation signals i.e. analog signal, low voltage digital signal etc.

2.8 Cable Armor: The metal stripes covering the high power cables.

2.9 Signal Ground: This is the return path associated with an analog signal.

2.10 Digital Ground: This is the return path associated with the digital logic signal.

3. Function of Plant Earth

The function of the plant earth is to limit over-voltages on the plant structure, equipment and

exposed metal sections. These surfaces may get electrically elevated from the zero potential of

earth due to high fault currents or due to lightning strikes. The plant earth conductor providesa path for these currents to the earth.


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4. Function of Primary Earth

The aim of the Primary Earth is to limit over-voltages, due to fault currents etc., on the

exposed Panel surface to ensure the personnels safety against electric shock hazards, refer

figure1& 1a. The Primary earth pit is a separate pit. The Plant earth pit must not be used asPrimary earth pit. This is to ensure that the momentary changes in the plant earth potential do

not directly reflect on the panel.

4.1 The Panel accessible parts, i.e. Panel chassis, framework & fixed metal parts, shall be

connected to the Primary Earth busbar within the Panel. This requirement can be met

by the normal structural parts providing electrical continuity. Paint may be scrapped at

the metallic joints to provide a good continuity.

4.2 Connections to Primary Earth busbar within the panel shall be such that connection is

maintained even when the Panel is opened or any removable part is removed.

4.3 Primary Earth pit shall be connected to the Plant Earth. This connection shall not be

just by the virtue of mounting of the Panel on the mounting rail or support on thefloor of the Plant. A cable shall provide connection between the Panel Primary Earth

bus bar and a separate earth pit. This earth pit shall be called Primary Earth pit. The

connection between the Primary earth pit and the Plant earth is described in section 6.

4.4 All the connections to the Primary Earth bus bar within the panel shall be of screw type

of brass or other non corrosive metal. The clamping means shall be adequately locked

against accidental loosening and it shall not be possible to loosen them without the aid

of a tool.

4.5 The Primary Earth pit shall have no other functions than those described above.

4.6 The Primary Earth pit shall be graphically represented as

4.7 Within the panel the Primary Earth wire shall be of color green with yellow stripes.

4.8 The gauge of the Primary Earth wire shall be,

! Within the Panel: 1.5 mm2, multistrand copper wire with insulation.

! Panel to pit: 10 mm2, multistrand copper or equivalent

aluminium wire, with insulation.

4.9 The following are connected to the Primary Earth:

4.9.1 The Panel.

4.9.2 The primary neutral terminal of all input/ isolation transformers.

4.9.3 Primary shield of all input/ isolation transformers.

4.9.4 Earth terminal of all Field Power supplies I/ O (External to the PLC System),

Displays, Switch matrix.

4.9.5 Incandescent Lamps & sockets.

4.9.6 All other parts of the Panel which are electrically isolated.


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Legend

1 Panel2 Primary earth busbar3 Secondary earth busbar4 Primary earth pit5 Control transformer6 Shorting of the primary sheild7 Plant earth8 Field power supply9 CPU power supply10 I/O ModulesP1, N1, E1 Primary power (100V/230V)P2, N2, E2 Seondary power (100VAC)P, N, E Auxillary power (230VAC)Dashed lines Not connected to primary earthSolid lines Connected to primary earth

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

Figure 1: Primary Earth

P2N2E2

P2N2E2

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

P1

N1

E1

P2

N2

E2

P N E

8

1

3

2

4

5

6

7

10

9


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1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4

Figure 1a: Primary Earth (Multiple feeds)

PS

P2N2E2

PS

P2N2E2

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

P N E

8

1

3

2

4

7A

P1

N1

E1

P2

N2

E2

5A

6A

P1

N1

E1

P2

N2

E2

5B

6B

10

9

Legend

1 Panel2 Primary earth busbar3 Secondary earth busbar4 Primary earth pit5A, 5B Control transformer6A, 6B Shorting of the primary sheild7A Plant earth8 Field power supply9 CPU power supply10 I/O ModulesP1, N1, E1 Primary power (100V/230V)P2, N3, E2 Secondary power (CPU)P3, N3, E3 Secondary power (I/O)P, N, E Auxillary p ower (230VAC)Dashed lines Not connected to primary earthSolid lines Connected to primary earth


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5. Function of Secondary Earth

Primary aim of the Secondary Earth is to provide low impedance path to the noise currents

induced by RFI/ EMI and the leakage currents in the PLC system. Refer to figure 2 & 2a.

5.1 All the metallic parts of the PLC hardware and the earth terminals on the I/ O modules

of the PLC system shall be connected to the Secondary Earth bus bar.

5.2 The PLC hardware must be isolated from the Panel by means of insulating spacers.

5.3 The Secondary Earth conductor from the Panel must be connected to a separate Earth

pit. This Earth pit is called Secondary Earth .Within the Panel the Secondary Earth bus

bar shall be isolated from the Primary Earth bus bar by mounting it on insulating

bushes.

5.4 All the connections of the Secondary Earth within the panel shall be of screw type of

brass or other non corrosive metal. The clamping means shall be adequately locked.

5.5 The Secondary Earth shall be graphically be represented as5.6 Within the panel the Secondary Earth wire shall be of color green.

5.7 The gauge of the Secondary Earth wire shall be:

! Within the Panel: 1.5 mm2, multistrand copper wire with insulation.

! Panel to pit: 6 mm2, multistrand copper or equivalent

aluminium wire, with insulation.

5.8 The following are connected to the Secondary Earth bus bar .

5.8.1 Secondary Shield of the transformer feeding the PLC Power supply Units.

5.8.2 Earth terminal of the Power Supplies for the PLC system (local I/ O, remote I/ O

interfaces & commutation devices).

5.8.3 All Mountbases, chassis of devices in 5.8.2.

5.8.4 Earth terminal of power line filter.


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1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

Figure 2: Secondary Earth (Single feed)

P2N2E2

P2N2E2

P1

N1

E1

P N E

1

3

2

4

P2

N2

E2

65

8

7

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2

10

9

11

Legend

1 Panel2 Primary earth busbar3 Secondary earth busbar4 Secondary earth pit5 Control transformer6 Shorting of the secondary sheild7 Mountbase8 Basic power supply9 I/O Module10 Sheilded I/O wire11 Sheild terminal on the I/O moduleP1, N1, E1 Primary power (100V/230V)P2, N2, E2 Seondary power (100VAC)P, N, E Auxillary p ower (230VAC)Dashed lines Not connected to secondary earthSolid lines Connected to secondary earth


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1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0

Figure 2a: Secondary Earth (Multiple feeds)

P2N2E2

P2N2E2

P N E

1

3

2

4

8

7

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 1

10

9

11

Legend

1 Panel2 Primary earth busbar3 Secondary earth busbar4 Secondary earth pit5A,5B Control transformer6A, 6B Shorting of the secondary sheild7 Mountbase8 Basic power supply9 I/O Module10 Sheilded I/O wire11 Sheild terminal on the I/O moduleP1, N1, E1 Primary power (100V/230V)P2, N2, E2 Seondary power (100VAC)P3, N3, E3 Secondary power (I/O)P, N, E Auxillary power (230VAC)Dashed lines Not connected to secondary earthSolid lines Connected to secondary earth

P1

N1

E1

P3

N3

E3

6B5B

P1

N1

E1

P2

N2

E2

6A5A


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6. Earthing of Multiple panels

6.1 Separate Primary and Secondary Earth conductor shall run from the Panel to the

Primary and Secondary earth pits respectively. Refer figures 3 , 4, 5 & 6.

6.2 In case of multiple adjacent Panels. The earth conductors of the non powered cabinets

must be connected to the respective earth busbar in the powered cabinet that hasconnection to the Primary and the Secondary earth pits respectively.

6.3 The earth conductors from the adjacent Panels shall be connected in a single point

termination. Daisy chaining of connection is not permitted. See figure 3.

6.4 Each Panel with separate power feed, on the same floor, shall run separate Primary &

Secondary earth conductors from the Panel to respective earth pits. See figure 4.

6.5 Each Panel with a separate power feed, on different floors / buildings shall run

separate Primary & Secondary earth conductors from the Panel to separate set of earth

pits or to common earth pits depending on the distance between the two locations. See

figure 5. (Minimum distance between Primary & Secondary Earth pits shall be > = 30

Meters.6.6 The Primary, Secondary and the Plant earth pits shall be shorted with each other. The

shorting shall be a single point connection. Daisy chaining of connections is not

permitted.

6.7 The wire gauge for interconnection of earth pits shall be 25 mm2, multistrand copper

or equivalent aluminum wire, with insulation.

Figure 3: Earthing of adjacent panels (With same power feed)

P2

N2

P1

N1

7

12

4 3 5

6

6Legend for figures 3, 4 & 5

1. Primary earth busbar2. Secondary earth busbar3. Secondary earth

4. Primary earth5. Plant earth6. Pit level earth short7. Transformer


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Figure 4: Earthing of adjacent panels (With different power feed)

Figure 5: Panels on different floors (With same or different power feeds)

4 3 5

6

6

3 54

6

6

1

2

1

2

1

2

P2

N2

P1

N1

7P2

N2

P1

N1

7


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7. Earthing of Panels with MultiplePower feeds

7.1 Same procedure as in section 6 to be followed.

8. Earthing of Remote Stations

8.1 Each Panel of the Remote station shall be individually earthed as in section 4, 5 & 6.

Refer figure 6.

9. Connecting MMI, Peripherals

This is aimed at the RS232 connection on the Modules used for interfacing PLC system to a

MMI, peripherals or other RS232 based system.

The aim is to isolate the ground/earth of the two system with the intention of breaking the

ground current loops formed by the potential differences between the two Systems ground/

earth.

The isolation may be achieved by means of intermediate device providing isolation betweenthe PLC and MMI system. This device may be external to the PLC / MMI System. E.g. RS232

optical isolators.

3 5

6

6

1

2

3 5

6

6

1

2

Distance between

two panels > 30m

7

44

Figure 6: Earthing of two remote panels

Legend

1. Primary earth busbar2. Secondary earth busbar3. Secondary earth4. Primary earth5. Plant earth6. Pit level earth short7. Communication cable


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10. Cables and Conduits

All communication cables should be run in conductive metallic conduits. The conduit should be

connected to the Plant earth not just by the virtue of its contact with the building steel. It

should be intentionally connected to the Plant earth at least at one location, preferably at

multiple locations. The conduits must not be directly connected to the Primary earth as they may

be prone to lightning strikes.

The Cable shields of the all the I/ O cables (analog signals, digital signals) shall be connected to

the Shield terminal identified on the respective I/ O module. They shall not be connected to any

other point in the System.

11. Verification of Earth Connections

11.1 Within the Panel

11.1.1 At the input of transformers the voltage across L to N & L to E should be same.

11.1.2 Measure the continuity of grounding electrode conductor from the earth pit (for

Primary & Secondary earth).

11.1.2.1 Disconnect the cabinet power supplies i.e. Complete shut down.

11.1.2.2 Lay a separate cable X1 from the primary earth bus bar in panel up to

the primary earth pit & ensure the continuity of X1 w.r.t. X

11.1.2.3 Lay a separate cable X2 from the Secondary earth bus bar in panel

upto the Secondary earth pit & ensure continuety of X2 w.r.t. X

11.1.3 Check the pit level continuity between Primary & Secondary earth.

11.1.4 Conduct megger test at 500V dc. This is to be conducted before mounting I/ Omodules or any other modules.

11.1.5 Measure the insulation between primary & secondary earth bus bars in panel,

these test should be reapeted at site with multimeter.

11.1.5.1 Disconnect Primary as well as Secondary earth out going grounding

conductor.

11.1.5.2 Connect a resistance meter (ohm meter) between Primary earth &

Secondary earth bus bar.

11.1.5.3 Observe the resistance. It shall be greater than 1 Megohm.

11.1.5.4 Re connect the Primary & Secondary Earth Conductors to theirrespective earth bus bars.


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11.2 Outside the Panel

11.2.1 Fall of potential method. (Refer figure 7)

Two auxiliary earth electrodes, are placed at a distance of 15m from the test

electrodes as shown in the figure 7. The test electrodes and the current

electrodes shall be so placed that they are independent of the resistance area of

each other. If the test electrode is in the form of rod or pipe ,the auxiliary

current electrode C shall be placed at least 30 meters away from it and theauxiliary potential electrode B shall be placed midway between them.

A known current is passed between the electrodes A & C and the potential

difference between the electrodes A & B is measured.

The resistance of the test electrodes A is then given by R = V/ I. The auxiliary

electrodes B & C usually consists of 12.5mm diameter mild steel rod driven up

to 1m into ground.

11.2.2 Impedance of earth electrode shall be less than 5 ohms.

11.2.3 Impedance of earth pit must be checked once in a year.

Figure 7: Fall of potential method(For measuring earth electrode resistance. Refer IEEE-344)

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

1 2

A

V~

Electrode "A"Test electrode

Electrode "B"Potentialelectrode

Electrode "C"Current electrode

" 15m #" 15m #

Above earth level

Below earth level

CurrentSource


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12. Earth pit

12.1 Typical installation of pipe earth electrode is shown in figure 8.

12.2 The distance between any two earth pits should be greater than 30 meters.

12.3 Keep the surrounding soil of the earth pit moist.

12.4 The effect of soil temperature on soil resistivity is more influencing near and below

freezing point, necessitating the installation of earth electrode at depths to which frost

will not penetrate. The minimum depth of the earth rod must be 2.5 meters.

Figure 8: Typical installation of earth pipe electrode(For detailed dimensions refer IS3043)

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

1 2 3 4

6 6

3 3

2

4 4

5

1

Above earth level

Below earth level

# "

ID=100mm

" 400mm #

"

2500mm

#

Legend

1. Concrete structure with lid2. Cast iron or copper pipe3. Homogeneous layer of

coke, charcoal, salt &sand4. Earth conductor (inter-pit

& equipment)5. Funnel for watering soil6. Exothermic bond or

brazing or connection bynon-ferrous, non-corrosive clamping device.


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13. Summary

13.1 Primary Earth connections:

13.1.1 The Panel.

13.1.2 The primary neutral terminal of all input/ isolation transformers.

13.1.3 Primary shield of all input/ isolation transformers.

13.1.4 Earth terminal of all Field Power supplies I/ O (External to the PLC System),

Displays, Switch matrix.

13.1.5 Incandescent Lamps.

13.2 Secondary Earth connections:

13.2.1 Secondary Shield of the transformer feeding the PLC Power supply Units.

13.2.2 Earth terminal of the Power Supplies for the PLC system (local I/ O, remote I/

O interfaces & commutation devices).

13.2.3 All Mountbases chassis devices in 12.2.3.

13.2.4 Earth terminal of the power line filters.

13.3 Dos:

13.3.1 Isolate the Mountbase from the Panel.

13.3.2 Run separate earth conductors to Primary & Secondary earth pits.

13.3.3 Short Primary, Secondary and Plant earth pits at pit level only.

13.3.4 Make Earth connections for Remote station similar to CPU stations.

13.3.5 Short the Remote stations & CPU station earth at the pit level.

13.3.6 Use port Isolators for RS232 communication port.

13.4 Donts:

13.4.1 Short Primary & Secondary earth bus bars within the Panel.


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ES3000

1Part-I(Rev.-

2)JULY2001

Control & Automation SectionLARSEN & TOUBRO LIMITED

!P.O. Box 7025, New Delhi 110002 Phone: (11) 372 1830 Fax: 371 3802!P.O. Box 8119, Mumbai 400051 Phone: (22) 654 1300 Fax: 654 1344

!P.O. Box 619, Calcutta 700071 Phone: (33) 242 2301/5 Fax: 242 7587/1025!Post Bag 5247, Chennai 600002 Phone: (44) 852 2141 Fax: 852 0769

Documents

Earthing Guidelines