MAN_Cable Laying Practices -1

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Electromagnetic Compatibility Contentsof Industrial Networks and Fieldbuses

Section Page

1 Summary and Definitions 3

1.1 Electromagnetic Compatibility (EMC) 3

1.2 Earth Ground and Machine Ground 4

1.3 Differential Mode and Common Mode 6

1.4 Shielded Cables 81.4-1 Choice of cable 81.4-2 Where should the connection be made? 9

1.5 Sensitivity of Different Cable Families 10

2 Wiring Rules 11

3 Wiring of Enclosures and Small Machines 13

3.1 Electromagnetic Caging 13

3.2 Protective Effects Inside an Enclosure or a Small Machine 14

3.3 Protection of External Connections to the Equipment 15

3.4 Internal Wiring of Enclosures 21

3.5 Using Cable Ducts 22

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Electromagnetic Compatibility Contentsof Industrial Networks and Fieldbuses

Section Page

4 Connections in Buildings and Large Machines 25

4.1 Electromagnetic Caging 25

4.2 Islands 26

4.3 Using Cable Ducts 284.3-1 Principle 284.3.2 General case 294.3.3 Methods for checking the length of uniform wiring 314.3.4 Methods for checking the length of mixed wiring 33

4.4 Other Protective Effects 34

5 Connections Between Buildings 35

5.1 Wiring Connections 35

5.2 Protection Against Penetration 36

Introduction

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This document (1) is intended for designers, contractors and installers of all SCHNEIDERELECTRIC installations containing digital connections.With the rapid changes taking place in industrial application electronics and for thereasons below it is no longer possible to ignore the problems of electromagneticcompatibility.

Equipment complying with industrial standards (electromagnetic compatibility) operateseffectively when it is stand-alone

Precautions should be taken, however, when devices are interconnected (networkedequipment, distributed control systems, remote I/O, etc) to ensure that they operateeffectively in their electromagnetic environment

For each installation configuration (fieldbus or industrial local network), ensure that thereare no additional requirements given in the relevant documentation (example : maximumlength, number of cable ducts, distance between two ducts)

Warning

CE marking is obligatory in Europe. It does not, in itself, guarantee the actualperformance of systems in terms of EMC.

(1) replaces the former guide "Wiring recommendations" TSX DG GND.

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Summary and Definitions 1

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1.1 Electromagnetic Compatibility (EMC)Electromagnetic compatibility is the capacity of a device or system to operate in itselectromagnetic environment without producing unacceptable electromagnetic interferencefor that environment or for any neighboring device.If problems occur (EM incompatibility), modification costs rise quickly when, in principle,many effective EMC solutions exist which are free of charge. Poor EMC choices can leadto high costs and should be avoided!

Section 11 Summary and Definitions

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1.2 Earth Ground and Machine GroundThe role of an earth grounding network is to discharge to ground all leakage and faultcurrents from equipment, common mode currents from external cables (mainly power andtelecommunication) and direct lightning current.Physically, low resistance (in relation to a distant earth ground) is much less relevant thanthe local equipotentiality of the building. In fact, the most sensitive lines are those whichconnect equipment together. In order to limit circulation of common mode currents oncables which do not leave the building, voltages between equipment interconnected on thesite must be limited.

Interconnecting buried networks is recommended. When the area of a building is small,that is, approximately ten square meters, a simple buried belt is sufficient. For newbuildings with a large surface area, we recommend linking buried conductors in a cagemeasuring approximately 10 m on each side.

Grounding belt of the buildingGrounding strip


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A machine or chassis ground is any conductive part of a device which is accessible tothe touch and, although not normally live, can become so if a fault occurs. The contactvoltage of two machine grounds which are simultaneously accessible must belower than the conventional contact limit voltage (25 or 50 V depending on the case).This is fundamentally all that is important in terms of safety of personnel, and in particularneither ground resistance nor the way in which machine grounds are earthed.

Electronic equipment and systems are (or are to be) interconnected. The best way ofensuring efficient operation is to maintain good equipotentiality between the differentdevices. Unlike safety of personnel which is an LF constraint, inter-device equipotentialitymust remain satisfactory, particularly for digital equipment, up to very high frequencies. In cases of incompatibility, safety rules take precedence over EMC constraints. In cases of incompatibility between the recommendations in this manual and specific

instructions for a device, the latter take precedence.

U

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IDM

IDMUDM

1.3 Differential Mode and Common ModeElectrical signals are normally transmitted in differential mode. All power supplies andelectronic signals are transmitted in differential mode. The current flows out along oneconductor and returns along the other. Differential voltage is measured between theconductors.

When the inward and outward conductors are side by side and separated from currentswhich cause interference, differential mode interference is negligeable in mostcases.

Common mode is an interference mode in which the current flows in the same directionon all the conductors and returns via the machine ground.

ICM

ICM UCM


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A machine ground (a conductive enclosure for example) acts as the reference potentialfor electronic signals and the reference return for common mode currents. Any commonmode current which, via a cable, penetrates a device isolated from machine grounds,leaves it again via the other cables. When machine grounds are inefficiently linked, a cablecarrying a common mode current has an interfering effect on all the others. Effectiveelectromagnetic caging reduces this phenomenon.HF interference transmitted along cables in common mode is the main EMCproblem.

The TN-C neutral point connection, by combining the neutral conductor (marked N, whichis live) with the protective conductor (marked PE) allows high currents to circulate throughthe machine grounds. This system is therefore harmful to the equipotentiality of the site andto the magnetic environment. The TN-S neutral point connection (with or without residualdifferential current protection) is far preferable.

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1.4 Shielded CablesA shielded cable provides excellent protection against electromagnetic interference,particularly high frequencies. The effectiveness of a shielded cable depends on the choiceof shielding and, even more importantly, on how it is installed.

1.4-1 Choice of cableThe choice of shielding quality depends on the type of connection. SCHNEIDERELECTRIC defines the cables for each fieldbus and local network so as to ensure theelectromagnetic compatibility of the installation.The problem with taped cables is their fragility. The protective effect of taped cables at HFis reduced as the cable is subject to different forces, such as traction and torsion.Single braid cables are the most common minimum solution for industrialapplications.

Average

Steel tape

Longitudinal drain

Good

Braid


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From a few MHz, the protective effect can reach several hundred MHz using a single braidif the shielding connections are suitable. Flexible, strong shielding makes installation fairlysimple, and is compatible with Sub-D or mini-DIN connectors.

1.4-2 Where should the connection be made?Unidirectional connection of the shielding prevents LF currents from flowing on thebraid. The shielding masks the LF electric field.Differential signals are thus protected in LF. In HF, this type of connection is noteffective.

Bidirectional connection of the shielding can be used to protect against the mostsevere interference : HF common mode.The problem with bilateral connections is that at low frequencies a current can flow onthe shielding (voltage between the two ends or looped field coupling). This currentgenerates a low voltage, sometimes called "hum", or 50 Hz noise, on the pair inside.

Both ends of the external shielding of all digital or power connections should beconnected to the machine ground at their point of entry into the equipment. Onlylow-level low frequency unshielded analog connections should be connected at oneend only.

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1.5 Sensitivity of Different Cable Families

Family Cables Comprising : EMC behavior1 Analog supply and measuring circuits These signals are sensitive

for analog sensors2 Digital digital and databus circuits These signals are sensitive.

and telecomm. They also cause interferencefor family 1

3 Relay volt-free contact circuits with risk of These signals cause interferencereactivation for families 1 and 2

4 Power supply supply and power circuits These signals cause interference

Wiring rules 2

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Whenever possible, installers must observe the following rules.

Rule no. 1 :The outward and return conductors must always be adjacent to each other.For digital or analog signals, the use of pairs is a minimum requirement. Special attentionshould be paid to wiring inside enclosures which use separated conductors. The wiresmust be labeled by signal type and by pair.Special case : the wiring for chains of emergency stop and alarm systems must never besingle wire point-to-point but in pairs.Rule no. 2 :Fastening all connections against grounding equipotential structures isrecommended in order to benefit from an HF protective effect.

The ideal would be to systematically use shielded cables or shielded multiple strands.However, the use of ducts for conducting cables provides a satisfactory level of protectionin most cases. As a minimum requirement, connection cables between or within buildingsshould also have a grounding connection : grounding wire or cable ducts.For connections inside enclosures and machines, cables should be systematicallyfastened against metal plate. In order to maintain the correct protective effect, the followingratio should be observed :

Distance between cablesRadius of thickest cable > 5

Section 22 Wiring Rules

Cable causinginterference

d

Signal cable

d/R > 5

R

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Rule no. 3 :Only pairs for analog, digital and telecommunication signals may be adjacent toeach other in the same bundle or laid in the same cable group.Relay, speed drive, supply and power circuits should be separated from the abovepairs.When installing variable speed drives, it is important to ensure that power connectionsare clearly separated from data links.

Whenever possible, a cable duct should be reserved for power connections inenclosures.

Rule no. 4 :The same connector should not be used for connecting different families (exceptfor relay, supply and power circuits).If the same connector is used for both analog and digital signals, these must beseparated by a row of pins at the 0 V connection.

Rule no. 5 :All unused conductors in a cable should be systematically connected to the chassisground at both ends (except for analog cables).This provides a protective effect with a factor of approximately 5 at HF.

Rule no. 6 :Power cables do not need to be shielded if they are filtered.

The power outputs of variable speed drives must therefore be either shielded or filtered.

Wiring of Enclosures and Small Machines 3

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3.1 Electromagnetic Caging

Linking the grounding elements inside an enclosure or a small machine is essential sincethese elements are directly accessible to electronic equipment. All the metal structuresof the bay will thus be interconnected. Equipotential connections for safety purposesmust be complemented by direct connections between all elements in the machine orenclosure.

Systematic use of a grid or cage at the back of the enclosure for mounting allequipment is recommended.

Warning : most protective coatings have an insulating effect.

Electromagnetic caging :DIN rail + enclosure ground

Mounting with electricalcontact

(lock washer)

Grounding stripSafety conductors

Electrical contact must be established for all mountings :REMOVE PAINT FROM CONTACT POINT

Section 33 Wiring of Enclosures and Small Machines

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3.2 Protective Effects Inside an Enclosure or a Small MachineThe presence of many grounding structures in machines and enclosures makes itpossible to benefit from a maximum protective effect.

All cables should be systematically fastened against the grounding elements.Plastic cable ducts are permitted in enclosures if they are systematically mounted onthe cage at the back or on DIN rails which are themselves connected to the groundsin the enclosure.

The design of enclosures means that many elements, including the doors, are onlymounted at particular points (using screws, welding, hinges, etc). This results in manygaps. Entry and exit of cables must be systematically located near these mountingpoints or duplicated by a grounding braid. This layout means the gap can be maskedand the protective effects thus maintained.

RILSAN clip

NO

YES

Grounding braid


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3.3 Protection of External Connections to the EquipmentMost of the problems encountered on site are related to conduction.

It is essential that all wiring connections outside enclosures or machines areprotected.

A grounding strip or Potential Reference Plate (PRP) will be defined for each enclosure andeach machine. All shielded cables and all wiring protection outside that enclosure ormachine should be connected to it.

This PRP can be one of the metal plates of the enclosure or its DIN cage. The PRP shouldalways be connected to the electromagnetic caging of the enclosure or machine andto that of the island (see section 4.2). In plastic enclosures (not recommended), a DIN railor grounding terminal should be used.

PRP

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Connection of shielded cablesThe way in which shielded cables are connected directly determines the HF protectiveeffect.

If the connection is made using a pigtail, that is, a single wire, protection is no longerprovided at HF.

A shielded fixed connection through the wall using a metal cable gland is the bestsolution, providing the paint is removed in order to ensure good electrical contact.A jumper can also be used, to ensure contact over at least 180.

Grounding strip


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Use of the pigtail is not recommended.

Poor

Fairly good

Groundingstrip

Good Excellent

PRP on chassis

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When connecting to screw terminals where use of a jumper for shielding connections isnot possible, the pigtail must be as short as possible. This type of connection should beavoided.

Ground terminals with metal mountingsystem using the DIN rail

No

Groundingstrip

YesAcceptable ifconnectionvery short


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When using a connector, its design must ensure 360 electrical continuity between thecable shielding and the machine ground.

Contact betweenthe connector shell

and shielding

Connector withgrounding bosses

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Installing filtersThe effectiveness of an AC power supply filter is determined at HF by its mounting ratherthan by its electrical operation. Three rules must be followed when mounting a filter : the filter must be referenced plate to plate the upstream and downstream cables must be wired on each side of the filter in order

to limit stray coupling between the input and output the upstream and downstream cables must be fastened against the plate in order to

limit radiation from the input to the output

Emissionand/orpick-up

No

No

Filtered conductor

Capacitive orinductivecoupling

Conductorsubjected tointerference

Fastenagainst the

plateFilter

Screw directly ontothe plate of the

chassis

Yes


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3.4 Internal Wiring of Enclosures

Numerical controllers, variable speed drives and PLCs can all occupy the same enclosureprovided that : the speed drives are installed with shielded cables all the wiring rules described above are observed : use a PRP or grounding strip for

example.

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3.5 Using Cable DuctsCable ducts outside enclosures must be made of metal if over 3 m long. These ductsmust have end-to-end electrical continuity and be directly connected to the groundsof enclosures and machines using trunking joints or connection bars.

Any other cable should only be used in cases where no other solution is possible.

If a single duct is used, it must be no longer than 30 m if possible. Unshielded cablesmust be fixed in the corners of the ducts as shown in the figure below.

Electrical contact must be established for all mountings :REMOVE the paint


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Vertical separation in the duct avoids mixing incompatible cables (see section 1.5). A metalcover on signal half-ducts is recommended. It should be noted that a full metal cover onthe duct does not improve EMC. Take possible future developments into consideration.

Power or speed drivecables

Relay cables

Shielded digital cables

Shielded analog cables

Unshielded digital cables

Unshielded analog cables

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Connections in Buildings and Large Machines 4

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4.1 Electromagnetic CagingSafety conductors (green/yellow) can be used to ensure the safety of personnel byinterconnecting low frequency grounds but this in itself does not ensurethe HF equipotentialityof equipment since the impedance of these conductors is too high (approximately 1 H/m). Electromagnetic caging is therefore necessary, that is, systematically interconnectingall the metal structures in the installation (framework, rails, sheathing, etc). A cage linkingmetal structures measuring approximately 3 m x 3 m is suitable.In particular, the chassis of enclosures and bays must be interconnected to nearbygrounds (cable ducts, casings, machines, framework, etc). A standard immunity test(IEC 61000-4-4) with repetitive steep front pulses can be used to quickly ensure correctlinking of grounds (cable ducts in particular) close to injection points and the shieldingconnections of shielded cables.

Crow's footBuried grounding belt

Principle of a grounding network

Iron strip

1 m

Lightningconductor(s)

Computerisland or room

< 2 mMetalcasing

Verticalgrounding

< 3 m

< 10 m

Section 44 Connections in Buildings and Large Machines

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4.2 IslandsExperience shows that in industrial environments, electronic equipment is generallygrouped into dedicated areas. Consequently, a grounding network does not have tocover the whole of a building. Instead, the islands grouping together electronicequipment should be defined. Sensor and actuator cables outside these islands mustbe carefully shielded.

When electronic equipment is grouped into an area which is larger than approximatelyten square meters, a cage measuring 3 m2 to 5 m2 should be created by interconnectingthe different grounding structures and enclosures.

Equipment

Vertical cableduct

Horizontal cableduct

Iron strip


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When equipment is grouped into several enclosures side by side, they are boltedtogether and thus make up an island.Conductive false floors can be used to create effective caging. For practical reasons, onlyone out of three supports needs to be connected. This then gives a cage of 1.80 m2.In this case the different grounding connections can be made using either copper roundbars, wide and short connector bars or tinned braid. Whenever possible, direct contactshould be made.

When two enclosures are side by side, they should be directly interconnected by at least2 contacts at the top and bottom of the bays.

Ensure that paint does not prevent electrical contact. The use of lock washers is highlyrecommended.

The cross-section of straps is not relevant since only their length is important. Thegrounding connections must not exceed 50 cm.

Interconnection of grounds

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4.3 Using Cable Ducts

4.3-1 Principle

All cables must be routed with protective effects by fastening them to groundingstructures.

Metal cable ducts with end-to-end electrical continuity should therefore be systematicallyused outside enclosures.

Use trunking joints to make the connections.It is very important that trunking joints or connector bars are used to make theseconnections rather than braids and particularly round conductors. These cable ductsmust be connected, using the same methods, to the grounds of enclosures andmachines, after removing any paint to ensure good contact.A vertical separation in the duct is used to avoid mixing incompatible cables (seesection 1.5).It should be noted that a full metal cover on these ducts does not improve EMC.

A backup cable (ground cable, see section 4.4) should only be used in cases whereno other solution is possible.

For each communication network, as a function in particular of its speed and the cablegauge used, a maximum initial limit for segment lengths (without repeater) must beobserved. This limit, shown in product documentation, may only be reached if theinstallation conditions are satisfactory in terms of EMC (in particular : cables laid inmetal ducts with end-to-end electrical continuity connected to electromagnetic cagingand earth ground).A maximum theoretical length for electromagnetic compatibility should thereforebe defined. This second limit is theoretical since it is usually greater than the firstone. It is used to optimize installation conditions and must be observed together withthe first limit. It also applies to a segment without a regenerative repeater.

equivalentto

equivalentto

+

-

Effectiveness


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4.3.2. General case

Two metal ducts should be used whenever possible : one reserved for power, relayand speed drive cables and the second for signal cables (sensors, data, telecommunicationsetc). The two ducts can touch if they are less than 30 m long. From 30 to 300 m, they shouldbe separated by 10 cm, either side by side or on top of each other. Over 300 m, they shouldbe 30 cm apart.

These special limits all derive from the same EMC Theoretical Length or ETL.Reaching this ETL assumes that the following three optimum conditions havebeen met :a - a second duct, at least 30 cm away, is reserved for power and relay cables,b - no more than 50% of the duct capacity is used,c - there are no analog cables or unshielded digital cables.

Relaycables

Analog cables(shielded)

Power cables

Digital cables(unshielded)

Digital cables(shielded)

Analog cables(unshielded)

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The EMC theoretical length is on average 1200 meters, but this value can varydepending on the type of communication network.

The ETL is : 2000 m for FIP at 1 MBit/s and for Unitelway, 1000 m for ModbusPlusand for Ethway with 50 Ohm triaxial cable, 700 m for Mapway, and 400 m for the X Bussystem used by PREMIUM PLCs.

Whenever one of the 3 conditions is not met over the total length, the physical length ofthe duct must be assigned a coefficient in order to maintain electromagnetic compatibility.These coefficients Ki, defined in the table below, measure the degree to which theprotective effect is reduced. The resulting authorized length will therefore be less thanthe ETL.

In addition, in the case of single ducts for power and signal cables, the coefficientwill, if necessary, take into account the absence of any metal separation or metalcovers on them.

Sym- Installation condition Coef- Totalbol ficient length (1)

Ki ETL x 1/KiOne or two ducts :

K20 Analog cable or unshielded 2 600 mdigital cable

K50 50% or moreof duct filled 2 600 m

K10 Ducts separatedby 10 cm (instead 2 600 mof 30 cm)

Single duct or two adjoining ducts :

K6 With separation and coveron signal half-duct 4 300 m

K8 Without cover on 6 200 msignal half-duct

K0 Without separation 12 100 m

(1) Maximum total length if this is the only unfavorable condition (with ETL = 1200 m)

or

or

10 cm10 cm

or


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4.3.3 Methods for checking the length of uniform wiringThe coefficients Ki can be used in two ways.To obtain the authorized physical length, start with the ETL and divide it by Ki (examples1 and 2 below).Conversely, in the case of actual physical lengths, these are multiplied by Ki and theresult compared with the ETL to check whether they comply with EMC requirements(examples 3, 4 and 5). If all of the signal cable is laid under uniform conditions, the maximum installation length

conforming with EMC requirements is obtained by dividing the ETL by each of the Kicoefficients in question (maximum of 3).

The physical length of the cable ducts must be multiplied by each of the Ki coefficientsin question (maximum of 3) to check that the ETL limit has not been exceeded.

Example 1 : Shielded digital connections less than 100 m, without analog cable.The connections can therefore be wired in a single metal duct (for ETL = 1200 m ormore).In fact - on condition that the duct is not more than 50% full - (take possible futuredevelopments into consideration), only coefficient K0 then needs to be taken into account,giving the maximum length 1200 m / 12 = 100 m.

Power cables and shielded digital connections should be fixed in the corners of the ductas shown in the figure below.

Relay cablesShielded digital cables

Power cables

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Example 2 : Shielded digital connections less than 300 m, without analog cableAs soon as the length calculated in an installation condition is no longer sufficient (100 min the first example) the EMC of the configuration must be improved.

A vertical separation in the duct is used to avoid mixing incompatible cables. A metalcover on the half-duct of signal cables limits the interference from signals.This is why the value of the coefficient then changes from 12 (=K0) to only 4 (=K6), giving(with ETL = 1200 m) the maximum length : ETL / 4 = 300 m.

The EMC conditions to be observed are thus : each half-duct is no more than 50% full the separation is made of metal and in contact with the duct throughout its length the cover is in contact with the separation throughout its length.

Take possible future developments into consideration.

Example 3 : Project for laying 60 m of signal cableYou wish to lay the cable in a single duct without separation, together with a power cableand an analog cable.This installation condition, based on the table of Ki symbols, is affected by twocoefficients : K0 (=12) and K20 (=2). The physical length should therefore be multipliedby 2 and by 12.Since the result of 1440 m (60 m x 24) is greater than ETL = 1200 m, the 60 m length installedin this way will not comply with EMC requirements. Example 4 (next section) provides apossible solution.

Shieldeddigitalcables

Powercables

Relaycables


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4.3.4 Methods for checking the length of mixed wiring When different installation conditions are present over the length of a cable duct, each

physical length of the same type must be multiplied by the relevant coefficientsfollowing the same rules as above.

The total of the different results must remain lower than the ETL (1200 m for example).

Example 4 : New project for laying 60 m of signal cableThe signal cable in example 3 is laid over 20 m using the type of installation describedabove. The remaining 40 m are laid, together with the analog signal cable, in one duct whichis separate from the power cable, but placed 10 cm away from the first one.

Length Ki coefficients Calculations Results

20 m K0 (=12) and K20 (=2) 20 m x 24 480 m40 m K10 (=2) and K20 (=2) 40 m x 4 160 mTotal (60 m) 480 m + 160 m 640 m

The result of 640 m now being lower than ETL = 1200 m, the 60 m length installed willcomply with EMC requirements.

Example 5 : Laying a FIP cable over 1000 mThe system documentation indicates that the first limit is observed provided that only trunkcable is used (1 large-gauge pair of 150 Ohms).

The ETL value for this system is 2000 m.Let us assume that the 3 optimum conditions (see section 4.3.2) are present over 700 mand that, over the rest of its length, the power duct is : more than 50% full only 10 cm away from the signal duct.

Length Ki coefficients Calculations Results

700 m none 700 m300 m K50 (=2) and K10 (=2) 300 m x 4 1200 mTotal (1000 m) 700 m + 1200 m 1900 m

The result of 1900 m being lower than ETL = 2000 m, the installed length will comply withEMC requirements and only the preceding condition remains (no small-gauge pairs used).

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4.4 Other Protective EffectsThe protective effect of a cable duct is approximately 50 between 1 MHz and 100 MHz.Other protective effects are possible in cases where this type of equipment cannot beused. Welded wire cable ducts are less effective and often more expensive than plateducting.

Welded wire cable duct :

Grounding cable :

Protective efffect 10

Protective efffect 5

Protective efffect 5Grounding cable

Connections between buildings 5

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5.1 Wiring ConnectionsConnections between buildings have two characteristics which can result in risks forthe installation : poor equipotentiality between the grounding elements of installations large loop areas between data cables and grounding elements.Before installing and connecting a data cable between two buildings, it is essentialto check that the two ground connections of the buildings are interconnected.All grounds which are simultaneously accessible must be connected to the sameground connection (or at least to a set of interconnected ground connections). Thisconstraint is fundamental for the safety of personnel.

The second risk related to connections between buildings is the loop area betweendata cables and grounding elements.This loop is particularly critical in the event of an indirect lightning strike on the site. Theovervoltages induced in these loops through indirect impact of lightning are in the order ofa hundred volts per square meter.

In order to limit this risk, all cables laid between two buildings must be duplicatedby a large-gauge equipotential connection ( 35 mm2).

Section 55 Connections Between Buildings

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5.2 Protection Against PenetrationCommon mode currents coming from outside must be discharged to the groundingnetwork at their point of entry to the site in order to limit any potential differencebetween equipment.

Any conducting trunking entering a building (conducting cable, conducting pipingor isolated piping carrying a conducting fluid) must be connected to the earthground at their point of entry to the building, using the shortest possible distance.Overvoltage protectors should be placed at the entry points in buildings for power,telecommunication and signal cables (data, alarms, access controls, video surveillance,etc). The effectiveness of such devices largely depends on their installation.Overvoltage protectors (varistors, arresters, etc) should be directly connected to theground of the electrical panel or equipment they are protecting. Connecting anovervoltage protector only to the earth ground (instead of the machine ground) is noteffective.

Whenever possible, the boards for power, telecommunication and signal protectionshould be located close to a grounding strip.

For data links between buildings, the use of optical fibre is highly recommended. This typeof connection is completely free of loop problems between buildings.

Earthground

Ground of the board

Ground of thetransformer

Upstream L.V.lightningconductors

ACsupplycable

Shieldedisolation

transformerNetwork

PE

Installation Wiring for PLCIntroduction1 Summary and Definitions 1.1 Electromagnetic Compatibility (EMC) 1.2 Earth Ground and Machine Ground 1.3 Differential Mode and Common Mode 1.4 Shielded Cables 1.4-1 Choice of cable 1.4-2 Where should the connection be made?

1.5 Sensitivity of Different Cable Families

2 Wiring Rules 3 Wiring of Enclosures and Small Machines 3.1 Electromagnetic Caging 3.2 Protective Effects Inside an Enclosure or a Small Machine 3.3 Protection of External Connections to the Equipment 3.4 Internal Wiring of Enclosures 3.5 Using Cable Ducts

4 Connections in Buildings and Large Machines 4.1 Electromagnetic Caging 4.2 Islands 4.3 Using Cable Ducts 4.3-1 Principle 4.3.2 General case 4.3.3 Methods for checking the length of uniform wiring 4.3.4 Methods for checking the length of mixed wiring

4.4 Other Protective Effects

5 Connections Between Buildings 5.1 Wiring Connections 5.2 Protection Against Penetration

Documents

MAN_Cable Laying Practices -1