If you aren’t familiar with the NFPA, here is a brief summary from their website:
“The mission of the international nonprofit NFPA, established in 1896, is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating consensus codes and standards, research,training, and education.” http://www.nfpa.org/
As I’m sure you are very aware, sensors and sensor cables end up on machines in every corner of the US. Check out the furniture testing displays the next time you are at IKEA, there are proxes and cables all over those things. On industrial equipment, the NFPA calls for very specific types of raw cable not to be used. These specifications are in the document NFPA 79. I’ve not encountered many private companies that enforce this standard to the letter; but many government facilities and contracts require that this standard be followed closely.
Exact Text of NFPA 79 2007 Standard
The exact text from NFPA 79 page 79-34 of the 2007 Edition states this:
22.214.171.124* Appliance Wiring Material. Single conductor or multi-conductor Type AWM shall not be permitted.
Exception: When part of a listed assembly suitable for the intended application, Type AWM shall be permissible.
With a simple glance at a normal sensor cable, alarms go off in my head. Most sensor cables are made with multi-conductor AWM type cables. Can I not use standard sensor cables on a government project?
Clarification of the Exception
I think the Exception part needs to be clarified a little bit to better understand this requirement. To make a general summary from the Exception, UL Recognized wire types are not permitted but Listed wire types are permitted. An AWM cable cannot be used UNLESS:
1) The raw AWM rated cable is used as a component in another assembly that is UL Listed. An example of this would be an overmolded cordset that is UL listed.
2) It conforms to a specific list of UL listed cable types. These can be found in the table below taken from chapter 12 of the NFPA 79 document.
But how do I even figure out if the cables I use conform to this or not?
Finding the UL Information
Information on the raw cable is usually printed on the cable jacket or can be found on the raw cable datasheet. For example, the raw cable used in a certain sensor cordset spells out the below information:
4/C 22AWG E41663 яU AWM2661 105°C 300V LL33361 CSA AWM I/II A/B 80°C 300V FT1
The “E41663 яU AWM2661” part of this number helps us find the detailed UL information by then using the UL website’s certification search engine.
This raw cable does not have any of the exceptions listed in the table above; so it, by itself, is non-compliant. If the raw cable did carry a PLTC or other approved rating it would be compliant by itself.
In the situation I have presented, the “E41663 яU AWM2661” raw cable is used in an assembly to make a certain sensor cordset. That particular cordset is UL listed, and thus the overall cable assembly is compliant to the NFPA 79 Standard.