In what scenario is it advisable to replace old knob-and-tube wiring?

Replacing old knob-and-tube wiring is advisable when it shows signs of wear or damage because this type of wiring can pose significant safety hazards. Knob-and-tube systems, which were commonly used in homes built before the 1940s, are often outdated and may not meet modern electrical code standards. Over time, insulation can deteriorate, connections may become loose, and the system may not adequately handle today's electrical loads, leading to potential overheating or electrocution risks.

Signs of wear or damage can include frayed wires, burnt marks, or exposed conductors, all of which indicate that the wiring is no longer safe for use. Addressing these issues proactively by replacing the wiring helps ensure the safety of the home's occupants and reduces the risk of electrical fires.

The other scenarios presented are less compelling reasons for immediate replacement. Selling the home can be a motivating factor, but it's not the only condition where safety should be considered. A new installation that complies with current standards does not apply because the question specifically concerns existing wiring that has already been installed. Lastly, while uninsulated and excessively long wiring presents concerns, any visible signs of damage are significant enough to warrant replacement as a priority safety measure.