What is the earliest type of residential wiring still observed in older homes?

Knob-and-tube wiring is recognized as one of the earliest types of electrical wiring used in residential properties, especially prominent from the late 1800s to the early 1900s. This system consists of individual wires that are run through wooden knobs for support and insulated with tubes where they pass through framing members. Its design was a significant advancement over previous methods, allowing for safer installation and insulation of electrical cables.

Though other options such as Romex and flexible conduit have become more common in modern wiring practices, they were developed much later. Romex, for instance, was introduced in the mid-20th century as a convenient way to wire homes with multi-conductor cables, which significantly differs from the older technologies. Similarly, metal-sheathed cable appeared after knob-and-tube wiring but is not as outdated as knob-and-tube itself. Therefore, knob-and-tube wiring remains the earliest type observed in older homes, highlighting the historical evolution of electrical systems in residential construction.