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a question about intrinsically safe instrument
What happens if we install an intrinsically safe instrument without installing a safety barrier before it?

As we know for any intrinsically safe instrument we should install a safety barrier to limit the energy fed to the instrument.

My question is: what happens if we install an intrinsically safe instrument without installing a safety barrier before it?

Will it operate/run well?

What will be its Ex protection capability in that case?

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The barrier is for Fire Safety.

You should know that it is based on the Area Classification for your section of plant.


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The instrument will operate and run properly. However, it will no longer be an intrinsically safe installation, it will not meet Ex requirements because in the event of a power supply failure there will be the capability of producing a spark with sufficient energy to ignite an explosive gas.

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The purpose of the I/S barrier is to prevent electrical faults (over voltage) in the safe area from getting to the I/S device in the hazardous, where the fault could damage the device and create an arcing-sparking ignition source.

No barrier; no protection from faults on the 'safe' side.

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You will find that most modern 2 wire instruments are supplied rated as general purpose NEMA-4, IS and explosion proof.

If you install it without an IS barrier it is only certified for GP service.

Install it is a proper IS loop with correct wiring and an IS barrier and it is rated IS.

Install it with the proper Ex-d rated conduit, fittings and cabling and it is Ex-d.

good luck

By Heinz Janiec on 28 September, 2019 - 9:57 am
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It may technically work, but it not legal to operate in a classified area. You will not be able to calculate the EX(i) proof, because you would not have the required data.

It is not a good idea to use it in this way in an classified area.

If you have it in a non classified area, it may be your choice, but you need to mark it so nobody can do something wrong.