Intrinsically Safe Circuits

M

Thread Starter

mriksman

I work in the middle east, and I see awful practices being performed every day. I do not profess to be an expert in the instrumentation side of things.

But I was concerned when I saw an instrument guy opening the cover of a Ex device in a hazardous location. When I approached him, he said "it's OK, there is a barrier to limit the power and prevent sparks."

Hell, even the device itself has labelled on the cover - DO NOT REMOVE IF CIRCUIT IS ALIVE. I am pretty sure BOTH barrier and device need to be Ex; the barrier manages power/shorts, and the device can store energy (hence why you shouldn't remove the housing).

Can someone provide a nice, technical explanation on my limited understanding of WHY the cover shouldn't be removed? What dangers are there if a barrier is "there to limit the power and prevent sparks."

Appreciated thanks.
 
OK, so after some research, my current understanding is:

Ex ia/ib devices can have their housing opened, display removed, and HART terminals connected in the field.

The warning IN EXPLOSIVE ATMOSPHERE KEEP TIGHT WHEN CIRCUIT ALIVE may not even apply. I read on one such Certificate of Conformity that the same housing is used on different instruments.

So - regardless of the body warnings, if the device has Ex ia/ib - the housing can be removed?
 
That is correct - provided the ONLY means of protretion is Ex ia/b/c. If the apparatus uses dual protection, such as Ex d ib, or Ex e ib, then there may be circuits that could cause ignition exposed if the enclosure is opened.

Also, anyone working on the apparatus needs to remember that all test equipment needs to be Ex i rated as well - anything applied to the circuit must be certified as being incapable of adding sufficient energy to cause a spark.
 
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