Understanding General Requirements of the NEC, Part 7

Article 110 provides general requirements for all installations. Section 110.12 is the famous “mechanical execution of work” part of the NEC. A recurring criticism of Sec. 110.12 is it’s not specific enough. It starts with “Electrical equipment shall be installed in a professional and skillful manner.” But there’s no explanation of what this means. We go back to the “Use and Application” Section of Article 90 and read the NEC is not intended to be "…an instruction manual for untrained persons” [Sec. 90.2].

Anyone who is “a qualified person” performing work in any trade knows what good workmanship means. Even so, the Informational Note for Sec. 110.12 identifies ANSI/NECA I-2015, Standard for Good Workmanship in Electrical Construction as a resource. It also says there are other ANSI-approved installation standards. The expectation is that a qualified person isn’t going to quibble over some rule to get by with something, but will instead consider his work to be his signature and take pride in doing it well. Even little touches occur to such a person. For example, he’s running EMT and notices a scratch running lengthwise. He turns this scratch to the wall so the umarred part of the EMT is facing out. There’s no rule book telling him to do this particular thing. He would not do this thing if the scratch were more than merely cosmetic; he would replace the damaged part.

Section 110.12 has only three subsections. It’s important to note that these three do not define professional and skillful work nor do they set its limits. They are three requirements that logically could go under some other Section but they are here and they fit. For example, unused openings are ugly and they show a poor appreciation for fit and finish. They are also dangerous. You have to close them up with a means that is substantially as strong as the enclosure wall [Sec. 110.12(A)].

The second requirement is that the equipment can’t be damaged [Sec. 110.12(B)]. There’s detail added, such as “damage” includes being contaminated or damaged by paint, cleaners, and other chemicals. You also can’t use parts that are bent, broken, cut or deteriorated by corrosion, chemical action, or overheating.

The third requirement applies to cables and conductors [Sec. 111.12(C)]. This mostly has to do with proper support and protection from damage. One aspect of this is any straps, staple, hangers, fittings, etc. you use must be designed and installed as not to damage the cable. One of the differences you may see between DIY installation of nonmetallic-sheathed cable (see Art. 334) versus installation by an electrician is the DIY installer typically uses flat staples instead of correctly-sized saddle staples. The result is the cable jacket is pinched too hard and thus damaged. The DIY installer will also typically cut this jacket back with a pocket knife and stretch the jacket trying to separate the two pieces, while an electrician will use wire strippers made for the purpose. The electrician does the work faster, and the workmanship is better.

Which brings us to an important point about doing work in a professional and skillful manner. It takes less time to work that way, partly because you use specific techniques to efficiently do the work. Another reason it saves time is you reduce rework dramatically. In the nonmetallic cable example, the DIY installer is likely to nick the conductors, which often means cutting off that chunk of cable and trying again. The professional and skillful electrician never has that problem.