C1D1 Experimental Sensors

[-Eddie-]

University students are developing passive sensors that will measure ammonium, pH, and oxidation reduction potential in an anaerobic digester (class I Div I Group D hazardous location). I am working with the students to understand requirements to deploy these sensors in an actual digester (before deploying, a PE will have to approve our plans). I understand that I'll need zener barriers and C1D1 cabling for this application, as well as entity parameters defined, but I am unclear what is required for sensor approvals.

If the sensors are purely passive, that is they have no electronics, they are just electrodes with a chemical treatment used to detect particular ions, what would be required to allow these sensors to be used in a C1D1 location?

 

[don_resqcapt19]

That is an equipment design question and not code question. There may be a product standard that covers the requirements for listing this type of equipment.

It sounds like you are talking about intrinsically safe equipment and such equipment is required to be listed per 504.4. I can't imagine any PE would approve the use of such a system without an actual listing. The might approve it, if you install it using the traditional Class I, Division 1 wiring methods as required in Article 501.

 

[-Eddie-]

Thank you Don.

Looks like our best hope is that our device will meet the definition of simple apparatus and the PE agrees.


NEC 504.2 Definitions
Simple Apparatus.
An electrical component or combination of components of simple construction with well defined electrical parameters that does not generate more than 1.5 volts, 100 milliamps, and 25 milliwatts, or a passive component that does not dissipate more than 1.3 watts and is compatible with the intrinsic safety of the circuit in which it is used.

 

[don_resqcapt19]

You still need to connect that simple apparatus to listed equipment, in accordance with the control diagram for the associated listed equipment

504.4 Equipment.
All intrinsically safe apparatus and associated apparatus shall be listed.
Exception:
Simple apparatus, as described on the control drawing, shall not be required to be listed.

 

[-Eddie-]

For listed equipment, you mean the cable and barrier? Does equipment on the non-hazardous side of the barrier need to be listed?

 

[don_resqcapt19]

For listed equipment, you mean the cable and barrier? Does equipment on the non-hazardous side of the barrier need to be listed?

The complete system needs to be listed for the use.

 

[-Eddie-]

Thank you Don.