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Principle of Intrinsic Safety - Explanation of Intrinsic Safety Technology - Phoenix Contact - YouTube


Z.

I will start off with a disclaimer as anything commented on this forum is based on the understanding gained from your post and may not be fully correct for the situation you have.


Having said that, you need to look at the whole installation and not just the individual parts. I am not sure what you mean by an 'Ex e' enclosure as the enclosure of itself doesn't have any electrical parts, but presume that it means an enclosure which if Ex e equipment was installed within would meet the Ex e requirements (such as IP rating, etc.). If you install Ex nA electronics within it then it will no longer be considered Ex e. I would also add that my understanding is that Ex nA electronics could be installed in a non-Ex enclosure but the enclosure would need to comply with the relevant part of IEC 60079.


I would suggest you probably need to discuss this in full detail with somebody who understands the ATEX Directive/DSEAR Regulations to make sure you are fully compliant.

Alasdair has pretty much covered it, but I'll add a few comments on some of your specific questions


>>I'm building an instrumentation system for use in Zone 2 Hazardous Areas and want to install electronics >>within an enclosure to process the sensor(s) data. The electronics enclosure I want to use is built and certified >>Ex e.


Ex e component certified enclosures are available. This means they will have been thermally conditioned (typically soaked at elevated temperature and high humidity for 4 weeks), then impact tested at 7J (1kg mass dropped from 700mm), and then IP tested to minimum IP54, often higher. This saves you having to have this testing done on your own enclosure. Obviously the certification is valid as long as you don't make any additional holes in the enclosure, other than entries for suitably certified glands, following the installation instructions as to correct hole size, use of sealing washers etc.


>>I understand Ex d enclosures housing non-Ex rated electronics must be designed and certified "as-built" by an >>approved manufacturer or notified body.


Do you mean Ex d or Ex e? I'll assume it was a typo and you meant Ex e.

You are correct that the finished product needs to be assessed. As above, the enclosure component certificate just saves you having to retest the enclosure. Everything you put inside has to be shown to be incapable of causing an ignition. Even Ex certified building blocks have to be reviewed to ensure they are used within their specific conditions of use and Service temperature etc. Eg an Ex nA ethernet switch or similar module will often have a requirement for an external transient suppressor to limit transients to <140% of rated supply voltage. You will very likely have to do a temperature rise test. Eg if the eth.sw is certified for an ambient of 50C, and you get a 10C rise inside the enclosure then the finished product will be certified for 40C max.


You are also correct that for Zone 2 products, they can be self certified by the manufacturer with no legal requirement for a Notified Body to be involved in the Type Testing or quality audits of the manufacturing. However, without wanting cause offence, the fact you are asking these questions strongly suggests to me it would be wise to get 3rd party verification.

Regardless of minimum legal requirements, customers may insist on 3rd party verification.


>>Can anyone advise on the following:

1. >>Does the system still conform to ATEX / Ex standards if all electronics installed within the Zone 2 >>rated Ex e enclosure are also Ex rated minimum Zone 2 (e.g. all are ExnA)?
   
   
   I think this is answered above.
   
    

• >>Can Ex nA electronics even be installed within a non-Ex (just Stainless Steel) encsloure with the >>right design parameters?
  
  Yes, as above. However starting with a component certified enclosure saves a lot of testing. For a one-off or low volume, it is a no-brainer. For high volumes, which I'm assuming this isn't, the situation is more nuanced.
  
   

• >>If I am supplying the enclosure with 24VDC power feed and RS485 comms ...do these feeds >>need to be intrinsically safe i.e. barrier protected to minimum Ex ib, or would over-current >>protection fuses suffice?
  
  As a general requirement, no the power supply doesn't need to be Ex ib. Many Ex products are mains powered for example. However, you do need to check the actual requirements for input/output/power connections for each bit of kit included. (Fuses/OPD may be required for various reasons but they are not fast enough to  prevent an ignition.)

>>Thanks in advance


You may also want to be aware that Ex nA is effectively obsolete, or about to be. It is no longer included in EN 60079-15:2019 and has effectively been replaced by Ex ec in EN 60069-7. The Date of Withdrawal of 60079-15:2010 is about April 2022 from memory. So if it takes you 6+ months to get this design to market, you have 6 months before the protection concept expires. Technically you can keep selling provided you do a gap analysis and reference it in your EU DOC. If this is a one off project, it probably doesn't matter. But if it is intended for repeat sales it is worth remembering. Also a) the Notified Body will probably steer you that way anyway and b) if you are using 3rd party kit they may force your hand because they will update their certification away from Ex nA.


Also, 'ATEX' still tends to be used as a generic term, but remember that from Jan next year you will need UKCA approval rather than ATEX if selling in Great Britain (NI is slightly different).  


Whilst notified bodies strictly speaking cannot act as consultants, most of them are quite helpful at steering you through the process. You really need to engage one or both. I can recommend a NB via PM if you want.

Hope this gives you a few helpful pointers.