I have basic doubt regarding snap acting pressure switches with Intrinsic safe.

To avoid arc during snap action / position of contacts change over, we need to limit the current to switch using barriers in the control room.There is no electrical part in the switch.Since snap acting pressure switches are passive components, is intrinsic safe protection for switch required?

May be my understanding might wrong. Pls correct and advise why intrinsic safe protection is required for switch.

And also I have one more doubt, in intrinsic safe loop whether all the instruments / components needs to be with intrinsic safe protection?
Please explain

 

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> we need to limit the current to switch using barriers in the control room. There is no electrical part in the switch. <

Yes, the switch doesn't 'store' any energy.
Yes, it could be a low power circuit that will not arc or spark with the energy contained in it.

But, the purpose of I/S barriers is to protect the hazardous area during normal operation, but to protect the hazardous area from faults in the safe area. A fault in a safe area can put unexpected amounts of energy into a normally low energy circuit.

Your switch connects to the control room via copper wires. Suppose someone accidently drops a wrench in a control panel. The wrench manages to break an AC hot wire crimp connector, free the wire, and expose part of the formerly insulated crimp connector. The 'hot' connector lands on the terminal of the wire coming back from your switch, applying its ac voltage.

High current flows through a normally low energy circuit. But before the circuit burns open, the switch in the hazardous area opens, creating a spark. Now you've got a spark in a hazardous area - an ignition source.

So it isn't the fact that your circuit is low energy under normal circumstances, it's the unexpected, unplanned for, accidental faults that I/S is there to protect from.

Whether my scenario is likely or unlikely in your specific circumstances (there's no AC in your panel), it doesn't matter. The path for large amounts of arcing/sparking energy exists in the copper wires running out to the hazardous area. You MUST protect against faults getting to the hazardous area. That's what I/S barriers and isolators do.

 

It's hard to edit or proof one's own writing. Correction, adding the word NOT:

But, the purpose of I/S barriers is NOT to protect the hazardous area during normal operation, but to protect the hazardous area from faults in the safe area.

 

>(Based in Usa and the NEC)

To answer your last quetion, NO, all instruments do not have to have intrinsic safety protection.

I.S. is merely one type of protection for electrical equipment operating in hazardous areas. The installation in a Class 1, div 1 area can be done, for example, using rigid steel conduit w/ proper explosionproof materials, enclosures, etc w/ conduit seals, etc. however, those methods and materials are much more expensive.