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I’m sure that all of you at one point or another have asked yourselves what is a manufactured wiring system. Well, maybe not all of you, but most of you…right? Well maybe not most, but some of you have... OK, so a couple of you have asked that question. The Code rules for manufactured wiring systems (MWS) are found in Article 604 and are quite easy to apply once you determine that, in fact, what you are looking at is a MWS.

The 1980 Report of the National Electrical Code Committee (NEC-TCR) contained two proposals for this type of wiring system. One was for a new Article 544 titled, Prefabricated Flexible Wiring Systems Type PFW, and another for a new Article 546 titled, Manufactured Wiring Assemblies. Responsibility for these was given to CMP-18 and a task force was formed to study them. The task force rewrote both proposals and recommended one new article titled, Manufactured Wiring Systems, which ultimately became Article 604 for the 1981 edition. A basic premise for this new article was to provide Code recognition for listed manufactured wiring assemblies that had been in existence since 1970 and had been installed in an estimated 40 million square feet of building space since 1976. Clearly it was time for the Code to establish rules for its installation. Responsibility for this article was shifted to CMP-19 for the 1984 Code and, with only relatively minor changes, most of the original rules remain in effect today.

Some of the confusion in dealing with manufactured wiring systems stems from the fact that there are two types of wiring assemblies marketed and, while similar in appearance, they are of somewhat different construction and designed for different purposes and use.

There are manufactured wiring systems (UL Category QQVX) which are investigated to UL 183 and intended for use in accordance with Article 604. Then there are wiring assemblies (UL Category QQYZ) which are not investigated to a particular UL standard but are intended for use in accordance with any NEC rules for the particular wiring method employed. Thus, the UL standard for that wiring method is what the product is investigated under. Manufactured wiring systems are typically comprised of cables, flexible metal, or liquidtight flexible conduit, with molded plugs, receptacles, or connectors that cannot be inspected on site without damage or destruction to the assembly. An exception was added to the 1999 NEC permitting a limited application of flexible cord for these systems [See 604-6(a) Exception No. 3]. They are also limited in use to accessible locations, with an exception of one end of a tapped cable being permitted to extend into hollow walls for direct termination at switch and outlet points. See Article 100 for the definition of "accessible (as applied to wiring methods)." This is an important distinction from wiring assemblies as they are permitted to be used where they will ultimately be concealed by the building finish.

Proposed changes for the 2002 NEC will clarify the acceptance of other types of cables used for systems identified in the scope of Article 604 and directly deal with support requirements for manufactured wiring systems as well as the uses permitted.

Your key to installing and inspecting these systems is to carefully review the listing mark to determine what type of system it is so you can apply the correct Code requirements.

Robert A. McCullough, director of Ocean County construction Inspection Department, is chairman of NEC® CMP-19 representing the IAEI, member of UL Electrical Council, IAEI Eastern Section Education Committee, Experior Assessments National Certification Program for Construction Code Electrical Test Development Committee, NFPA Task Group on the Usability of the NEC®, HUD National Manufactured home Advisory Council, and chairman of New Jersey State Electrical Subcode Committee.

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