Whoever performed this installation must not have even known that the NEC has rules for temporary wiring.
While it's true that, by necessity, the NEC rules for temporary wiring are not nearly as strict as those for permanent installations, there are still rules. One that's been violated here is the concern for “protection” of the conductors. Section 590.4(H) states, “Flexible cords and cables shall be protected from accidental damage. Sharp corners and projections shall be avoided. Where passing through doorways or other pinch points, protection shall be provided to avoid damage.”
Although that wording doesn't specifically prohibit the temporary wiring from being strung across this staircase, the basic requirement to essentially route and locate the cables so as to prevent damage has not been satisfied — therein lies the problem. It seems pretty clear that people traveling up and down those stairs are going to (at some point) come in contact with the cables and either pull the conductors apart or trip and injure themselves. A little bit of common sense can go a long way toward providing a safer working environment for job-site personnel, not to mention offering a modicum of legal protection for the installer.
Another problem is the means of support — or lack thereof. Part (J) of 590.4 says, “Cable assemblies and flexible cords shall be supported at intervals that ensure that they will be protected from physical damage. Support shall be in the form of staples, cable ties, straps or similar fittings installed so as to not cause damage. Vegetation shall not be used for support of overhead spans of branch circuits or feeders.”
In this case, the installer failed to support the conductors in manner that will prevent damage, which is a violation. In addition, although not visible, the installer used electrician's tape as a means of support. Tape is not specifically identified, and it doesn't seem to me that tape is a “similar fitting,” as required by the wording of this rule.
We know the wording of 90.3 provides guidelines on “which rules apply when.” As this section states, “This Code is divided into the introduction and nine chapters, as shown in Fig. 90.3. Chapters 1, 2, 3, and 4 apply generally; Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions. These latter chapters supplement or modify the general rules. Chapters 1 though 4 apply except as amended by Chapter 5, 6, and 7.” With the foregoing in mind, one can immediately see that the rule of 110.12, “Mechanical Execution of Work,” must be satisfied. Here, the Code says, “Electrical equipment shall be installed in a neat and workmanlike manner.” No one in their right mind would characterize this knotted mess of cables as “neat and workmanlike.”