Friday, December 30, 2016

Electrical Conductors, Electrical Wires and Electrical Cables - Explained

Electrical Conductors, Electrical Wires and Electrical Cables

 Over the past 30 years the term Conductors, Wires and Cables have been intertwined in a world of misunderstanding and potential misapplication. This article will attempt to bring clarity to these terms for everyday use in the electrical industry from a manufacturers perspective.

The best way to begin to understand the differences is to attempt to define them in my own words.

Electrical Cable(s) - Electrical cable(s) are an assembly consisting of one or more conductors with their own insulations, individual covering(s), and protective jacketing.

Electrical Wire(s) - a thread or strand of copper or aluminum, typically manufactured from 5/16” or 3/8” solid copper or aluminum rods, then reduced down through a series of forming dies into specific standardized sizes and ultimately used as bare or insulated electrical conductors with thermoplastic, thermosetting or other listed insulating material along with additional coverings, where required by it’s associated UL Standard.

Electrical Conductor(s) - an electrical conductor, of the wire type, is an electrical wire, available in solid or stranded design, and is produced to allow the flow of electrical current in one or more directions. A copper or aluminum bare or insulated electrical wire is a common electrical conductor of the wire type.

While these definitions are my interpretation of their meanings, it is also important to understand that not all electrical conductors are actually of the wire type. There are other electrical conductors in the electrical industry that are not of the wire type yet considered to be electrical conductors. We are only focusing this article on the wire type of electrical conductor.

When you examine the term electrical cable, the reader has to understand that cables can be of the single or multiple electrical wire type. The single electrical wires of a cable would have the same basic electrical cable elements as a multi-conductor cable, having a core electrical wire, typically with an insulating material prescribed by the governing standard to which it is being constructed and used as an electrical conductor, which is ultimately protected by an outer jacket or sheathing, where required by the UL Standard. The combination of these elements creates a single cable. In a multi-conductor cable you have multiple electrical wires, grouped or cabled together to form the core, which is ultimately jacketed in a protective sheathing to form a completed, and UL listed cable assembly.

It is this author’s opinion that simply twisting or cabling electrical wires together doesn’t automatically create a cable assembly. Those would simply be electrical wires, being used as electrical conductors, which are simply twisted or cabled together to form the core design of an electrical cable assembly. All cable assemblies have to be listed by a Nationally Recognized Testing Laboratory (NRTL) and constructed in accordance with Underwriters Laboratory (UL) exacting standards. It is also important to understand that there are indeed cable assemblies that do not have an protective jacket yet are still UL listed for a specific application, for example, Deep Well Submersible Pump Cable which can come with or without a protective jacket or sheathing as long as it is listed and labeled for the specific application of use in accordance with UL. Simply twisting or cabling individual electrical wires would not by itself constitute a cable assembly unless it has been evaluated, listed and labeled as such.

 Now in support of this article we only need to examine the National Electrical Code [NEC] to see how the various terms are used. In Article 310, the code is clearly referencing conductors. The familiar conductor allowable ampacities, adjustments and corrections tables found in section 310.15 reference conductors and their association with how they are to be used. Chapter 3 of the code references the various acceptable wiring methods, which all of the cables associated are to be of the listed type.

The transition from a manufactured electrical wire to what the NEC considered an electrical conductor, of the wire type, is theoretically being transformed within Article 310 of the NEC. The articles within chapter 3 begin to take those electrical conductors and utilize them into listed cable assembly types for use in the building wiring industry.

Now, let’s look at the UL White Book, which I affectionately call the extended edition of the National Electrical Code. In examining the section titled “ Wire and Cable Markings”, the reader will quickly get an idea of what UL considered a wire versus a cable. Clearly electrical wires can be constructed into a cable assembly for ultimate listing and labeling but the difference is quite evident. In some cases like Type USE-2 cable, you indeed have individual electrical wires, now transformed into electrical conductors of the wire type, with or without a protective jacket or sheathing that have indeed been evaluated for use as a cable in or itself. However, what is clear is that you simply do not call an XHHW-2 or a THHN/THWN-2 a cable when it is indeed within the eyes of UL and the NEC an electrical conductor of the wire type, which was transformed from being manufactured as simply an electrical wire.

Lastly, while I do not put a lot of assurance in “Google™” searches, and the results below confirm this position, I did a search on the following phrase “ What is the difference between a wire and a cable” and the search results are interesting, which as expected I do not 100% agree with:
 “A wire is a single conductor (material most commonly being copper or aluminum) while cable is two or more insulated wires wrapped in one jacket.”

As we have seen it doesn’t technically take two or more insulated electrical wires or electrical conductors of the wire type to be considered a cable, and clearly in many cases the protective jacket or sheathing is optional. What is clear is that all cables have to be listed and labeled for their specific use and taking individually UL Listed electrical wires or electrical conductors of the wire type and twisting them together do not guarantee they are to be considered a cable assembly.

As opinions will vary, the goal here was to attempt to simplify the basic understanding of the differences in electrical conductors, electrical wires and electrical cables and I hope we have succeeded in that effort.

Update: Clearly the 2017 National Electrical Code and Code Making Panel 8 agreed with my interpretation as evident in this Chapter 9, Table 1, Note 9 change in the 2017 NEC :

"Assemblies of single insulated conductors without an overall covering shall not be considered a cable when determining conduit or tubing fill area. The conduit or tubing fill for the assemblies shall be calculated based upon the individual conductors"

Paul W Abernathy, CMI, CPI
CEO & President of Electrical Code Academy, Inc.

 References: 2014 UL White Book - Guide Information For Electrical Equipment
                       2014 National Electrical Code (NEC-NFPA70)

 NEC and the National Electrical Code are registered trademarks of the National Fire Protection Association and in no way endorse my opinions within this article.

UL is a registered trademark of Underwriters Laboratory and in no way endorse my opinions within this article.

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