Hazardous Location and Intrinsically Safe Barrier Requirement for Simple Apparatus'


New member
Have a question I have been mulling around for a while now.

There is an explosion proof motor located in a Class I Division 1 location, the motor has RTDs (simple apparatus) for winding temperature monitoring. Are the RTDs required to pass through an intrinsically safe barrier, or is it exempt from that protection technique because it is located within an explosion proof motor.

The same question would go for submersible pump with leak and overtemp detection. Pump is explosion proof but there are simple apparatus' within it.

I have trouble understanding whether devices protected by one protection technique (explosion proof) would have to comply with another (IS).

Any guidance would be appreciated.


Staff member
Mission Viejo, CA
Professional Electrical Engineer
The simplest response is the motor enclosure is irrelevant. Unless the "simple apparatus" is installed in accordance with a control drawing [Section 504.10(A)], it isn't part of an IS installation. If it is installed in accordance with a control drawing, then any suitable wiring method [Section 504.20] (subject to proper sealing and separation) is acceptable.
"Simple apparatus" ceases to be simple apparatus as soon as it's integrated into other equipment. So, my first response would be that the RTDs are no longer simple apparatus because they're incorporated into the motor.

Also, per the usual IS analyses, the RTDs could fault to the motor windings and (presumably) become energized well beyond IS ignition limits. Thus, attempting to wire them as IS, and/or allowing the RTD connections to exit the explosion-proof envelope, would not be allowable.

Attaching the RTDs to an IS barrier that lives ouside the Div 1 area would not help. Barriers are designed to keep energy outside the Div 1 area from entering; they are not designed to limit energy already within the area.

(I guess if you somehow integrated an IS barrier into the XP motor to limit the worst-case energy exiting the explosion-proof envelope, that would work. But that would seem stupid, not to mention extremely impractical.)

From this, the RTDs would have to be wired as for a non-IS system, with appropriate Div 1 wiring methods (i.e. conduit or armored cable), exactly the same way that the motor itself would be. They could not be considered as simple apparatus.