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Can anyone advise on IS (intrinsic safe) or non-IS cable to wire up a transmitter/device? Does it depend on the type of the device, location of the device, whether it is located at hazardous area, current rating of the device, or other factors as well? I appreciate that anyone can advice... Thank you.

There is no such thing as an IS cable. Cables used in IS loops (between haz area mounted devices and safe area mounted interfaces) have certain parameters that they have to respect.

Please give more details of your application so we can give you more concrete information.

Steve
MTL
www.mtlblog.com

Dear Steve,

Thank you for your reply. My understanding of IS or non IS cable is as follows, and correct me if I'm wrong.

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. If I'm not mistaken there are no special requirements for construction of an IS cable, but I'm not sure whether any other special requirements to be complied with such as construction (ex., stranding size), conductor materials (ex., Fe, Cu, Al, T/C), parameters (ex., inductance & capacitance...

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, and for non IS circuits the cable generally use black sheathing on the outer. During construction these cables have to be segregated to differentiate the circuits.

An example of application is I want to connect a flow transmitter, flow control valve with positioner and turbine flowmeter at Zone 2 area. How do I determine whether it is an IS or non IS circuit for these devices, thus using a different cable to connect it plus have to install barrier at the DCS panel for the IS circuits? Your advice is very much appreciated. Thank you.

Firstly, you need to decide whether the loop will be IS or not as there are other techniques that can be used for Zone 2. Best guide for this is your company standard practices or rules. If this is an existing plant, how are other loops protected?

If it is to be IS, then the transmitters and positioners will need to be IS and protected by suitable barriers/interfaces mounted in the safe area. There are constraints for the cables used between the two, these mainly concern the insulation thickness and you will need to refer to the appropriate Installation standard for your country (e.g. EN60079-14 in the EU). There are restrictions on cable inductance and capacitance, but unless you have a IIC risk with long cable lengths, you will not have problems. Marking/segregation will again depend on the installation standard applying in your country.

If you want to email me offline, I will forward some of our Technical Literature.

Regards,

Steve
MTL
syates(AT)mtl-inst. com
www.mtlblog.com