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We have a PLC in a Local Panel in Hazardous area, for the selection of the field instruments can we opt or Ex i transmitters with Barriers in the LCP. Normally barriers are located in Safe area and provide Isolation from Hazardous area. Hence please let me know if it is a good engineering practice to put barriers in field?

I see now reason why not except that the barriers would need to be approved for installation IN the hazardous zone. Or is the panel they will be in Z-purged?

The other way is to wire the transmitters Ex d or perhaps Ex e.
Either way you should get your inspectors interpretation before you start.

Regards,
Roy

I have previously done this by installing the IS barriers in a (suitably sized) Ex d flameproof box. Alternatively, if you do have a pressurised enclosure for your PLC, then the internals of this box should be non-hazardous, provided the box is certified Ex p.

Not sure of your situation here, however wiring from the Ex d box to your PLC may pose an issue, and you will need to be careful to ensure correct cable/gland selection, etc for this, if you go this way.

Where you are installing your panel? Zone 2?

If yes Barriers/isolators are available to be mounted in Zone 2 FROM truck. But in any case you need to have purge panel, which makes it Zone 2 area.

Jari
iconcnl [at] vsnl.net

Talk to your barrier supplier to see what certification they have for their barriers. MTL, for whom I used to work, had certification that allowed their passive zener barriers to be mounted in zone 2/div 2 in suitable (not Ex'd') enclosures. I think there were plans to get similar approval for the active (isolated barriers)

Steve

Dear Steve,

Thanks for your valuable comments. I will certainly get in touch with the vendors. But the enclosure selection is another big problem as client insists that all instrumentation shall be rated for Class1, Div1. Can you throw some more light on teh enclosure suitable for barriers.

You didn't say it was Div 1 in your original question so my answer may have been off track. Again I would talk to the manufacturer of the barriers you want to use, or his local rep and ask them to recommend an enclosure that they know will be acceptable to the authorities in the country you are working in (Local regulations in some countries are far stricter than in others)

Steve