Which of the following is NOT a condition that installations must be free from, as per NEC guidelines?

In the context of the NEC, installations are indeed required to be free from certain electrical conditions that can create hazards, including ground faults, short circuits, and inappropriate connections to ground. Each of these conditions can lead to unsafe situations, requiring attention and mitigation through proper installation practices and maintenance.

Electrical resistance, while it is a natural characteristic of circuits and conductors, is not classified in the same risk category as the others. Resistance is simply a measure of how much a material opposes the flow of electric current, which is an inherent property of electrical components. Instead of being a hazardous condition, managing resistance is part of the normal functioning of electrical systems. Therefore, it does not qualify as a condition that installations must be free from according to NEC guidelines.

Understanding the nature of these conditions helps clarify why some are critical to avoid, and others, like electrical resistance, are necessary properties that must be managed rather than eliminated.