Intrinsically Safe Circuits

ProjectDelta

Member
Location
Michigan
Occupation
Electrician
I’m currently working on a paint booth project and am trying to understand some of the concepts behind the installation. We have several intrinsically safe circuits running to different instruments within the booth. The circuit runs from inside the booth, through a seal off to the clean room (unclassified location, and into a cable tray with several other circuits both IS and otherwise. It then comes to an enclosure where the barrier is located. My question is:

Is the circuit considered “intrinsically safe” through it’s entire length from the instrument to the barrier?

If it is not, at what point is the circuit no longer defined as intrinsically safe? The reason I ask is because I want to know if the requirements of separation apply and at what points do they apply. My thought is that a short circuit or ground fault that occurs outside of the class I division I location would not cause a spark. Therefore, a circuit would not need to be considered IS. Hoping someone can help clarify this concept for me as I’ve only been in the trade 3 years. TIA
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It seems to me that contact with a foriegn voltage source outside the Classified Area could compromise the IS status of the circuit within the Classified Area.
That in turn seems to me to justify applying separation rules to the entire length.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
See Section 504.30 for specific requirements. Essentially, everything downstream of the barrier(s) must maintain the separations indicated. Incidentally, the control drawing requirements Section 504.10 will often also indicate additional separations.
 
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