Use of IS Barrier for Intrinsically Safe Instruments

Yes.

The barrier prevents electrical faults in the safe area from getting into the hazardous area.

Barrier absolutely required. Yes. Yes.

Our friend Iris is correct, one need to protect IS barrier although fieild instruments are of selected based on particular Group / Zone. For instance the instruments are usually powered through 24V DC supply but what about load. For any unforeseen reason if any mishap occurs then how sure that this load is insufficient to get a spark or flame or static charging. More over, you stated that it is a lube oil refinery hence safe design first.

We see very poor practice of people using ATEX field instruments but the most danger zone which is neglected is the control panel and it's lead wires in and out of control panel.

The factory supplied wiring diagrams for hazardous areas are very explicit about barrier or isolator protection.

You need not think at all about this point.

Just follow, whatever is specified in ATEX / FM certificate. There, you will find that the certificate not only asks for using external barrier, but also will specify the entity parameters of the barrier to be used.

Intrinsic safety is a method of protection where the voltage and current levels in the hazardous area are too low for an incendive spark capable of igniting a potentially explosive atmosphere to occur.

Therefore some method of preventing higher voltage/current levels from outside the hazardous area getting into the hazardous area is required.

The PLC is outside the hazardous area and the instrument is inside the hazardous area.

Therfore a barrier device is needed between the PLC and the field instrument, and the instrument manufacturer's instructions may even state the parameters of the barrier that is required.

Is the selected interconnecting cable correct?

DO NOT SELECT, INSTALL OR TEST HAZARDOUS AREA EQUIPMENT WITHOUT HAVING RECEIVED AN APPROPRIATE LEVEL OF TRAINING!

Risk of

Intrinsically safe field equipment is only approved for use in Zone 1 environments when used with approved intrinsically safe barriers (ISBs).

As others in this forum have stated, the device itself can not garuntee that current through the conductors would be limited in the event of a short circuit or damage to the device, thus all conductors that feed IS devices must be completely isolated from non-IS wiring (even within panels) and supplied by ISBs.

ISBs do not have to be located in the PLC panel; they can be located anywhere you want to put them, if you follow the installation guidelines correctly.