Reply to original poster
Reply to original poster
I would like to start at the original question.
If I use a listed NEC Class 2 power supply with rated output below the ignition curves, does this make my circuits nonincendive and therefore able to feed NRTL approved nonincendive and intrinsically safe field devices; and use non-hazardous location wiring methods, quick disconnects and simple devices, such as switches, without intrinsic safety barriers?
The relatively easy answer is NO. Product defined as associated apparatus or used within a hazardous location (field devices) must be certified by an OHSA approved NRTL. A Class 2 power supply has been evaluated against fire or shock hazard. As part of this evaluation, there is no consideration as to its ability to cause/prevent ignition of a hazardous location. It seems simple enough to say that the Class 2 power supply must be safe as long as the voltage/current output is below the ignition curve. It?s true - physics state that a point below the ignition curve will not ignite the specified hazardous ?classified? area. However, there is more to consider.
Let?s deal with intrinsic safety first. A device is only considered intrinsically safe (associated apparatus or a field device) after multiple fault conditions are introduced at random places within the product and after additional safety factors of at least 50% (sometimes even more) are applied to the output as well as to the rating of components within the circuit. An intrinsically safe device is only safe after it meets a wide range of electrical and mechanical requirements. OSHA has granted the NRTL?s as the only agencies able to claim a product meets the requirements specified in the appropriate standards for safety. A Class 2 power supply is not evaluated to the appropriate ANSI standard(s) for intrinsic safety (or nonincendive/Division 2). Next, let?s consider nonincendive, this type of device does not normally have faults considered as part of an evaluation for safety; however, the output parameters are still just a small part to the overall certification of a product that is allowed to be connected to an NRTL approved field instrument or simple apparatus.
Simple apparatus, such as switches and quick disconnects, are not required to be certified by an NRTL but they still require connection to a certified intrinsic safety barrier or nonincendive barrier to operate within a hazardous location.