Instrument/Electronic protection for equipment working in hazardous areas (with flammable gas) requires Ex certified protection.

So far I have come across a few common protection method: Ex'd' (Flame), Ex'e' (Increased safety) & Ex'ia', 'ib', 'ic' (Intrinsic Safety).

So far I only know the definition of them, but apart from Ex'd' which prevents explosion from coming out of the enclosure, I have problem understanding Intrinsic Safety & Increased Safety.

What is the difference between Ex'd' & Ex'e'? Is it more on testing to make sure equipment is safe or do they apply certain things to keep it safe?

Also regarding Intrinsic Safety, all i know is they keep the voltage low so it won't cause ignition, utilize some enclosures, barriers like Zenger but if somebody knowledgeable can give a proper explanation and brief methology would be great.

I tried reading IEC 60079 but it's too detailed and deep for me to understand the basic fundamentals of these protections.

 

Go buy Ernie Magison's book from ISA. It has been the bible for decades.

Walt Boyes
Editor in Chief
Control and Controlglobal.com
www.controlglobal.com

Mailto:[email protected]
Read my blog SoundOFF!! At www.controlglobal.com/soundoff

 

A brief summary of the different methods ...

Ex d flameproof - an enclosure can contain equipment that can cause ignition, and the external atmosphere can penetrate the enclosure. If ignition does occur, the effects are confined to the enclosure interior and not passed to the external atmosphere. OK in Zone 1 and Zone 2.

Ex e Increased Safety - the risk of ignition due to electrical effects is greatly reduced by attention to detail in terminations (making sure there is very little chance of a terminal coming loose, etc), reducing specifications for voltage and current-carrying capability, specifying minimum separations between potential-carrying parts, etc. OK in Zone 1 and Zone 2.

Ex i intrinsically safe - explosion protection involves maintaining the energy level in electrical circuits in the flammable atmosphere below a level that could cause ignition by limiting voltage and current, and controlling circuit inductance and capacitance. Comes in 2 flavours - Ex ia is specified to be safe with 2 internal faults and is good for all zones, while Ex ib is safe with 1 fault and can be used in Zone 1 and Zone 2.

Ex n non-sparking - is actually a catch-all for different methods, most of which are reduced-performance of the above. Ex n is safe in normal service but not necessarily under fault conditions, so is good for Zone 2 only.

Then there are all the others - Ex m encapsulation (which also comes in a and b variants); Ex o oil-filled, Ex p pressurisation, Ex q sand-filled. And of course the dust versions - Ex iD IS for dusts, Ex pD, Ex tD protection by enclosure ...

For a bit more info contact me off-line and I'll flick you a pdf version of some teaching notes I have available. bmdurdle !at clear !dot net !dot nz

 

Thanks, may i know how to contact you offline thankyou.

Also interested in how Intrinsic safety actually works with all these barriers.

dot nz

 

Email address was given at the end

- bmdurdle !at clear !dot net !dot nz

Replace the words beginning with ! with the relevant symbols ...

Cheers,
Bruce