Post by Electrical Code Academy Staff on Apr 28, 2016 12:16:22 GMT -6
Greetings Folks,
As many of you know I wrote a blog that shed some light on the true meaning of "electrical wires, conductors and cables" for clarity and a better understanding of what constitutes what in the cable and wire manufacturing business. However, I eluded to the fact that simply pre-twisting or "plexed" conductors in our factory (or anyones factory for that matter) does not create a cable in itself. To define what is considered a cable for use in the National Electrical Code we have to look at the "NFPA Glossary of Terms" which was published (updated) in 2014. In that document is has the term "cable" and then references the definition for use in NFPA 70 (NEC) as follows:
Cable - A factory assembly of two or more conductors having an overall covering. per the 2014 Glossary of terms by the NFPA. They again reference this document to NFPA 70 for the effective use of the term Cable in that minimum safety standard.
Now, in order to be a cable it has to be a factory assembly (basically think of a Type MC Cable without the armor applied, it is pre-twisted prior to armoring)..that is simply a factory cabled assembly and nothing more. Once it is placed with an "overall" outer covering then it becomes a cable.
There is a lot of confusion out there in the NEC as well when you see terms like Single Conductor Cable......yet how does it meet the basic concept of Cable as defined by NFPA in their glossary of terms, but i digress.
So I am asked...what about USE-2 Cable? It is a single conductor cable and it does not contain two or more conductors with an overall jacket. The answer is easier than you think. Notice the below glossary term for Service Entrance Cable.
Service Entrance Cable - A single conductor or multiconductor assembly provided with or without an overall covering, primarily used for services, and of the following types:
As you can see and as I stated in my blog there are specific construction allowances to be considered a cable as part of its manufacturing and Type USE has that listing.........it is evaluated as such.
Simply taking THHN/THWN-2 or XHHW-2 and pre-twisting them, placing them on a reel and shipping them out does not mean it is a cable....it is simply individual conductors that are pre-twisted "plexed" which has some advantages in the pull...less contact friction, less change of jaming and results in many cases with an easier pull. However, it does not mean you can twist conductors together and then use the 53% fill allowance in Chapter 9, Table 1, Note 9.....typically USE-2 is one of the components for URD or UDC cables which are indeed individual cables because they are evaluated to UL-854 and are clearly defined in the NFPA Glossary of Terms as we examined.......so just plexing or pre-twisting THHN/THWN-2, XHHW-2, RHH, RHW-2 does not mean you have a "cable"....you just have twisted individual conductors.
Now in theory the 53% fill for those twisted cable should not be an issue and there are advantages but as the codes stands now it is not what I would call "CODE" but to each his own. I think a well constructed public input could change that but far be it for me to carry that sword as I like the 40% fill just fine.
FYI- Those are my opinions so please by all means feel free to state your case or present your own thoughts.
As many of you know I wrote a blog that shed some light on the true meaning of "electrical wires, conductors and cables" for clarity and a better understanding of what constitutes what in the cable and wire manufacturing business. However, I eluded to the fact that simply pre-twisting or "plexed" conductors in our factory (or anyones factory for that matter) does not create a cable in itself. To define what is considered a cable for use in the National Electrical Code we have to look at the "NFPA Glossary of Terms" which was published (updated) in 2014. In that document is has the term "cable" and then references the definition for use in NFPA 70 (NEC) as follows:
Cable - A factory assembly of two or more conductors having an overall covering. per the 2014 Glossary of terms by the NFPA. They again reference this document to NFPA 70 for the effective use of the term Cable in that minimum safety standard.
Now, in order to be a cable it has to be a factory assembly (basically think of a Type MC Cable without the armor applied, it is pre-twisted prior to armoring)..that is simply a factory cabled assembly and nothing more. Once it is placed with an "overall" outer covering then it becomes a cable.
There is a lot of confusion out there in the NEC as well when you see terms like Single Conductor Cable......yet how does it meet the basic concept of Cable as defined by NFPA in their glossary of terms, but i digress.
So I am asked...what about USE-2 Cable? It is a single conductor cable and it does not contain two or more conductors with an overall jacket. The answer is easier than you think. Notice the below glossary term for Service Entrance Cable.
Service Entrance Cable - A single conductor or multiconductor assembly provided with or without an overall covering, primarily used for services, and of the following types:
As you can see and as I stated in my blog there are specific construction allowances to be considered a cable as part of its manufacturing and Type USE has that listing.........it is evaluated as such.
Simply taking THHN/THWN-2 or XHHW-2 and pre-twisting them, placing them on a reel and shipping them out does not mean it is a cable....it is simply individual conductors that are pre-twisted "plexed" which has some advantages in the pull...less contact friction, less change of jaming and results in many cases with an easier pull. However, it does not mean you can twist conductors together and then use the 53% fill allowance in Chapter 9, Table 1, Note 9.....typically USE-2 is one of the components for URD or UDC cables which are indeed individual cables because they are evaluated to UL-854 and are clearly defined in the NFPA Glossary of Terms as we examined.......so just plexing or pre-twisting THHN/THWN-2, XHHW-2, RHH, RHW-2 does not mean you have a "cable"....you just have twisted individual conductors.
Now in theory the 53% fill for those twisted cable should not be an issue and there are advantages but as the codes stands now it is not what I would call "CODE" but to each his own. I think a well constructed public input could change that but far be it for me to carry that sword as I like the 40% fill just fine.
FYI- Those are my opinions so please by all means feel free to state your case or present your own thoughts.