Uses and limitations of intrinsically safe I/O

[Megabyte]

Hello,
I am working on a control system which contains devices in a classified area (class 1, div1 --Alcohol vapors normally present). I have selected all intrinsically safe devices and am using an intrinsically safe barrier. My layout is like this:
|.........control enclosure..........|
|unclassified area (outside) |-------->|SEAL OFF|------->| classified area with field devices|
|IS barrier for all IO.................|

I would like a check on my understanding:

• The seal off is placed to prevent vapor from returning to the control enclosure
• Once in the classified area, do I need class 1 div1 rated conduit and misc. parts if the devices and source are intrinsically safe?
• I'm not sure why I would, if the current is limited from the barrier, there shouldn't be any risk within the conduit. But I could be wrong on this.
• Can someone please point me to the relevant code sections?

Additional information:

• Field devices are 24vdc and 12vdc
• There are a few pneumatic valves with IS components and asco IS rated solenoids
• Aside from that, it's flow meters and switches all IS

Thank you for your time and assistance!

 

[tom baker]

There is a specific UL listing for IS control panels.We have some moderators who are experienced in IS systems and they can review and comment. My advice is to provide the classification per 500.4 to a UL IS panel shop, it will be less expensive and safer to have them fabricate your panel. They need to know what devices do it can be listed as a system
There is an article on IS systems, it’s maybe 504, that would be good to review

 

[rbalex]

Do you have a control drawing? Along with Tom’s comment with respect to a classification document, a control drawing is essential.

Article 504 is also essential. The scope references the ISA Standards that should also be followed.

Your “lay out” confuses me a bit. It appears you have the IS barriers inside the Classified location. That is a big no-no.

Sealing is covered in Section 504.70.

Grounding and bonding requirements are in Sections 504.50 and 60. They are more complex than you might imagine.

Other Sections on circuit separations may also surprise you.

IS it’s not the magic solution many think it is.