We do use pair cable for digital signals too. For eg.HART - here high freq digital signals are superimposed on a current loop of 4 - 20ma on a two wire pair cable. IS and non IS is not clear. Do you mean Indian standards by IS? Please clarify.
It's not the cable that is I.S. or Non-I.S. it's the circuit!
An Intrinsically Safe (I.S.) circuit is where the current is limited, so that there is insufficient energy to cause a spark and is normally used in hazardous areas. Analogue circuits normally use a shielded twisted pair because it provides better noise immunity, digital circuits do not normally require the same level of noise immunity.
Outer sheath is Blue. They are normally used for Analog Signals i.e. Signal Cables. It will have individual for each pair as well as over all cable shields.
Non IS Cable: Non Intrinsically Safe (Circuits) Cable.
Outer sheath is black.
They are normally used as Control as well as Signal cables. It may have only an over all cable sheath or individual pair + over all shield according to Client's specification requirements.
I think the IS you are referring to might stand for Intrinsically Safe. This is a method of preventing a circuit carrying enough energy to ignite an explosive atmosphere of gas or dust. Non IS and IS cabling must be segregated to a certain extent to prevent voltages from non IS circuits coming into contact with IS circuits under fault conditions. A good link to get some information might be http://www.mtl-inst.com/support/tp.htm. This is orginally a British compnay specialising in the manufacture of this type of equipment.
Pair cable for analogues is used as the method of construction of the helps prevent the signal being interfered with by sources of noise. Important for accurate measurement not so important for on/off signals. digital communication cables are also likely to be pairs for the same reason as analogues as the previous repsonse indicated.
Like most questions relating to explosion-protection methods, the answer to this one depends on the local regulations, if any. If there are no applicable regulations in force, you should follow the IEC 60079 standards for gas or vapour service, IEC 61241 for dusts. In general, there are *no* special requirements or restrictions on cable methods in an IS system - except for the limitations on cable capacitance and inductance, which will be specified as part of the energy limiting device's entity parameters. There is a convention that IS circuits will be identified by a blue sheath, but this is not a requirement of the standards.
There is a world of difference separating (excuse the pun) IS and Non-IS cable, as different as apples and oranges:
The major differences are related to construction (ex., stranding size), conductor materials (ex., Fe, Cu, Al, T/C), parameters (ex., inductance & capacitance), connections (ex., terminal distances), and most often overlooked (at least in the USA) installation (ex., circuit segregation)!
The thing that makes a cable IS is that it is being used to carry IS circuits, with energy limitations imposed on them by some external energy limiting device such as a zener barrier or isolator. There are NO special requirements for construction of an IS cable - at least in the IEC standards, and as far as I understand them also the US ones. In fact, IS circuits are specifically excluded from many of the restrictions placed on wiring methods specified for other methods of explosion protection.
The only special requirement for cables carrying IS circuits is that they must be specifically identified as such, and they must be segregated from other non-IS circuits. The usual convention is to use blue sheathing on the cable outer, but this is not a code requirement - tape-on labels stating "THIS CABLE CARRIES IS CIRCUITS" placed every meter or so would also be acceptable.
The length and electrical properties of the cable must be such that the maximum permitted values of circuit inductance and capacitance are not exceeded, but this is a value that has to be calculated for the circuit as a whole and not just the cable.
This is referred the difference between Non I.S. and Non I.S. Cable.
Refer to application, I.S.normally applical for hazardous location or in an explosive atmosphere wherein explosive Gas is presence or applicable on only in Zone1&2 classification or it could be used also in Zone1/2&3 depends on client specification. the colors it could be blue or gray and with overall shield and with individual drain on n each conductor and shall be twisted pair thus protected the noise RFI
Non I.S. could be used only in Zone2/3 area of classification. the color might be black only as indentification.nonn I.S. could be twisted pr and overall shield only this is the commonly used now in oil and gas industry or petrochemical.
Hope this could clarify the issue
>I think the IS you are referring to might stand for
>Intrinsically Safe. This is a method of preventing a circuit
>carrying enough energy to ignite an explosive atmosphere of
>gas or dust. Non IS and IS cabling must be segregated to a
>certain extent to prevent voltages from non IS circuits
>coming into contact with IS circuits under fault conditions.
>A good link to get some information might be
>http://www.mtl-inst.com/support/tp.htm. This is orginally a
>British compnay specialising in the manufacture of this type
>of equipment.
>
>Pair cable for analogues is used as the method of
>construction of the helps prevent the signal being
>interfered with by sources of noise. Important for accurate
>measurement not so important for on/off signals. digital
>communication cables are also likely to be pairs for the
>same reason as analogues as the previous repsonse indicated.
