Cable Design Parameters

8/16/2019 Cable Design Parameters

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Before we start with the details of the software bit, let’s have a look at what instrumentation cables

actually are, and what makes them different from other cables.

In essence, a cable is two or more wires running side by side and bonded, twisted or braided together to

form a single assembly. In mechanics, cables are used for lifting, hauling and towing or conveying force

through tension. In electrical engineering, cables are used to carry electric currents. An optical cable

contains one or more optical fibres in a protective jacket that supports the fibres.

They may look unassuming, but they are indispensable when it comes to the transmission of electric

power or electronic data, and they assure that mechanical systems function well.

Instrumentation cables are multiple conductor cables that convey low energy electrical signals used for

monitoring or controlling electrical power systems and their associated processes. The functions of

measurement and control are vital in manufacturing and processing applications. These functions are

greatly dependent on their electronic circuitry. Typical applications include industrial euipment control

broadcasting, assemble euipment, or mass transit systems.

Cable Construction



As discussed before, the different layers that a cable is made up of can be understood by studying the

following!

". ". #$%&'#T$(!

)*cept for thermocouple e*tension and compensating cables, shall be solid, stranded or fle*ible plain or

metal coated copper in accordance with class ", + or in the range of -.mm+ to +.mm+. or multi/

core cables the ma*imum conductor resistance shall be as 0& 121, and for finished multi/pair, multi/

triple and multi/uad cables the ma*imum resistance of 0& 121 shall be increased by +3.

#onductor joints shall be as )% -+22/".

4tranded and fle*ible conductors shall consist of wires circular in cross section assembled, without

insulation between them, by concentric stranding or by bunching.

5hen the installed length of cable results in a high conductor resistance. 6arger conductor si7es can be

used.

". +. I%4'6ATI$%!

The insulating material can be selected from those listed below.

A8 9:#

B8 9olyethylene

#8 9olypropylene

&8 0alogen free flame retardant compound

)8 #ross/linked polyethylene



The minimum thickness at any point of the insulation shall not be less than the ones specified in the

standard for the specified voltage rating, and the concentricity shall not fall below ;3. There may be

occasions when cables are reuired to have higher operating temperature ratings than those provided by

using the materials specified by )% -+<- series. 4uitable alternative materials are under consideration.

". 1. #AB6) )6)=)%T4!

The lay length of a pair, triple or uad shall not e*ceed "--mm for cables with conductor cross section

>? ".mm+, nor "-mm for cables with conductor cross section +.mm+.

". @. I&)%TII#ATI$% $ #AB6I% )6)=)%T4!

'nless otherwise specified e.g. by means of numbered cores or tapes, the coding for identification shall

be as given in I)# -"2</+ or )% -;-2, as appropriate. The colours shall meet the reuirements of @.@

of )% -+22/".

#oloured or numbered non hygroscopic binder tapes maybe applied over screened cabling elements as

identification.

". . 4#())%I% $ #AB6I% )6)=)%T4!

5hen screening of individual cable elements is specified, it shall be selected from those listed below and

applied in accordance with @. of )% -+22/".

A8 A plain or coated metal braid with a minimum filling factor of -.

B8 A combination of a foil, and a plain or coated metal braid with a minimum filling factor of -. The use

of a drain wire is optional when this type of screen is appliedC

#8 A foil applied with a minimum overlap of +-3 with a drain wire in direct contact with the metallic

side of the foil.

". . #AB6) =AD)/'9!

The cable elements shall be assembled together in concentric layers or in unit constructions to form the

cable core.



The cable core assembly shall be protected by wrappings of non/hygroscopic tape.

4uccessive layers maybe separated from each other by interlayer binders of non/hygroscopic tape.

". ;. I66I% #$=9$'%&!

5hen a filling compound is specified, it shall be selected from the compounds given in )% -+<-/+/+2

and shall meet the reuirements of @.; of )% -+22/".

". 2. I%T)(4TITIA6 I66)(4!

5hen filters are used they shall meet the reuirements of @.2 of )% -+22/".

". <. 4#())%I% $ T0) #AB6) #$()!

The cable core shall be protected with a protective layer as described in "" or "1. 5hen it is covered

with a screen.

5hen screening of the cable is specified, it shall be selected from those listed below, and applied in

accordance with @.< of )% -+22/"!

A8 A plain or coated metal braid with a minimum filling factor of -.

B8 A combination of a foil, and a plain or coated metal braid with a minimum filling factor of -.1. The

use of drain wire is optional when this type of screen is appliedC

#8 A foil applied with a minimum overlap of +-3 with a drain wire in direct contact with the metallic

side of the foil.

4creening over the cable core may also be in the form of a laminated sheath.

". "-. =$I4T'() BA((I)(4!

5hen a moisture barrier is specified it shall be selected from those listed below. It shall be applied to

meet reuirements of @."- of )% -+22/"!



A8 5ater swell able tapesC

B8 5ater swell able non/to*ic powderC

#8 illing compoundC

&8 6aminated sheath, consisting of longitudinal overlapped metal foil, bonded within the overlapping

and to the inner surface of the e*truded sheath. The foil shall be one or both side plastic coated, but in

the case of only one side being coated a thin copper drain wire shall be applied in direct contact with the

metallic surface of the foil. The thickness of the metallic part of the foil shall be at least -."mmC

)8 #ombinations of these four methods.

". "". 9($T)#TI:) 5(A99I%4!

A wrapping layer maybe applied under the sheath.

A wrapping layer maybe applied under a metallic protection layer.

The wrapping layer shall be of a material compatible with the cable components with which it is in

contact.

". "+. I%%)( 40)AT0

5hen an additional inner sheath is applied under a metallic sheath E@."@8 and may be applied under a

lead sheath E@."28, it shall be selected from the materials listed below.

A8 9:#

B8 9olyethylene

#8 0alogen free flame retardant compound

The nominal thickness EI4(t8 shall be calculated like the nominal thickness E4(t8 of the outer sheath

without metallic protection E@."8.

A 0alogen free flame retardant compound shall be used where the cores are insulated with a halogen



free compound.

There may be occasions when cables are reuired to have higher operating temperature ratings than

those provided by using the materials specified by )% -+<- series. 4uitable alternative materials are

under consideration.

". "1. B)&&I% 6AF)(4!

A bedding layer shall be applied between a lead sheath and a metallic protection. This layer maybe

e*truded Ematerials as in @."+8 or comprise helically applied tape or tapes.

The bedding layer maybe e*truded when gland diameter reuirements re specified.

There may be occasions when cables are reuired to have higher operating temperature ratings than

those provided by using the materials specified by )% -+<- series. 4uitable alternative materials are

under consideration.

". "@. =)TA66I# 9($T)#TI$%!

=etallic protection when specified shall be in accordance with @."@ of )% -+22/".

5hen round or flat galvani7ed steel wires are used, the minimum thickness shall be -.2-mm. lat

galvani7ed steel wire may only be applied to cables where the diameter under armour is G"mm.

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Cable Design Parameters