What is the difference between IS and Non-IS cables?

[sivaranjith]

IS cables means intrinsically safe and non IS means non intrinsically safe. IS cables are used in intrinsic safety circuits. Before we look into the IS and Non IS cables we have to know about intrinsically safe circuits.

Intrinsic safe systems are indented to use in the hazardous locations where there is a high chance of ignition.

Intrinsic safety system, wires, earthing

What is an intrinsic safe system? A system, comprising apparatus and interconnecting wiring, in which any spark or thermal effect in any part of the system intended for use in hazardous areas is incapable of causing ignition. The cause of ignition is controlled by using barriers in the circuit and by using IS cables. Intrinsic safety is the only techniques considering faults in the connecting cables. Why is intrinsic safety should be implemented in hazardous area? Many field instruments such a…

Intrinsic safe circuit:

Intrinsic safe circuits are those in which no spark or thermal effects generated during normal and specific faulty conditions.

Every equipment used in the hazardous zone including resistors, capacitors and wires should be intrinsically safe.

An electrical circuit, no matter how complex it is, is examined sequentially as resistive, inductive and capacitive. If the different types of circuits satisfy the safety criteria, the circuit can be considered intrinsically safe.

What is the difference between IS and Non-IS cable?

Non IS cables are used in non-hazardous area, where no special consideration is needed in case of safety.

When designing the Intrinsic system all components used must satisfy the required specification.

The cables that are safe in faulty situations, protected from damage caused by the external electrical or magnetic field and used in intrinsic circuits are called intrinsically safe cables or IS cables.

In IS cables, additional sheathings are used to avoid mechanical damages. The cable is coloured as blue. The length and electrical properties of the cable must be such that the maximum permitted values of inductance and capacitance of the circuit are not exceeded, but this is a value that must be calculated for the circuit as a whole and not only for the cable.

Features of IS cables:

• Blue colour

• Must withstand 500v in insulation test done for 1 minute.

• Protected by sheathing materials such as polyurethane.

• The selection of IS cable is based on the transmitters used and the overall value of capacitance and resistance.

• They are normally used as Control as well as Signal cables.

• The analog pair cable is used as a method of construction of the aids to prevent the signal from being interfered with by noise sources.

• Marking of Is cables is not necessary if either the Is or non-Is cables are armoured, screened or metal sheathed.

• IS is the only technique which permits live working without gas clearance certificates.