intrinsic and cl1 div 2 VS barriers

It's not a plc question but it's often comes with it...

Do some of you know exactly when we need to add an intrinsec barrier in a CL1 div 2 panel and when we don't.

I use to install them for my 4-20mA loop and for my on/off but i bet in some case i'm over designing it and lose some jobs

i have an actual application to retrofit where i would need to connect a CL1 div2 plc to a 4-20mA transmitter with internal isolation but not rated cl1 div2
The plc is in a cl1 div2 zone where the transmitter is in a safe zone...

Zone classifications

As far as i know you would use the barrier when your cabinet is in a safe zone and the instrument is in a hazardous area.


As for panels that are within a hazardous area the barrier would not be effective you would need a different explosion prevention techinque. In this case i would say purging the panel with nitrogen. Obviously the panel would need to be sealed properly to accomodate this.
Here is a link to other posts on this site.

http://www.plctalk.net/qanda/showthread.php?t=17671

Hope this helps
R