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Plant Automation/Controls/Intrinsically safe USB barrier


Robert wrote at 2009-05-11 17:32:36
Hi Steve,

I would like to add to Mike's answer.  Your vendor is correct you MUST use a barrier that has Class I Div 1 rated USB outputs. You cannot just simply run a standard USB cable out to your field device, this will violated installation and NEC regulations and result in a very dangersituation, if too much voltage or current get out to your field device.

As Mike said I would start with your vendor and see what his suggestion is.  If I would check with company's that deal with IS barriers.

One last note, once you find an IS barrier, make sure you check the entity parameters of the barrier with the Entity of the field device, to make sure they comply with the NEC standard and to ensure intrinsic safety.

I hope this helps.

Best regards,


Spark Institute wrote at 2013-04-22 21:23:40
Sorry to disagree, but there is no way that you would be allowed to connect "ordinary" USB equipment directly to a piece of intrinsically safe equipment in a Division 1 area.  A barrier will be required.

Though USB would fall under the I.S. limits for normal operation, that does not mean it is safe to use.  The worst-case scenario for such a bus would be, effectively, an AC mains line direct into the hazloc, which is obviously not terribly safe.  A barrier is required to ensure that this does not happen and ignition limits for the target explosive atmosphere are not exceeded.

Moreover, the scale should have operational limits known as "entity parameters" defined.  Exceeding these parameters will cause the I.S. certification of the scale to become invalid.  The barrier used will need to be chosen to meet these entity parameters.

"Normal" USB equipment - i.e. not hazardous locations rated - would also not be allowed in the Division 1 area.  Or any hazardous area, for that matter.  

Most such equipment would likely qualify for Division 2 use - if the vendor could be bothered to acquire such a certification for it, that is - but "will likely qualify" and "has been qualified" are two entirely different things.

Unfortunately I do not know of any potential suitable barriers - I was searching for the same thing when I ran across this post.  

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Mike Nager


General range of knowledge of industrial controls and connection technologies as well as B2B Sales and Marketing.


Industrial controls including Moore Products (now Siemens), Leeds & Northrup (now Honeywell), ifm efector and Phoenix Contact.

former Director of ISA's Food and Pharmaceutical Divion, BiSCI, WEF, Chairman Integrated Systems and Controls of Material Handling Industry of America (MHIA),

Authored technical articles in Industrial Computing, I&CS, WEFTECH, Control Engineering, PackWorld, Modern Material Handling, Control

BS Electronics Engineering from the University of Scranton

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