Disadvantages of Knob and Tube Wiring
-Knob and tube wiring system does not incorporate a ground. The ground wire on any circuit is the most important wire, as it is there for safety. Also, some electronic equipment requires a ground to operate correctly.
-Switched neutrals. Electricians in the early 1900’s would switch the neutral feeding a ceiling light instead of the hot wire, which is today’s standard. Switching the neutral, would turn off the light, but live voltage potential would still be present at the fixture. Making a dangerous situation for a homeowner that is trying to change the light fixture.
-Insulation becomes very brittle and breaks down when heated too much. Older light fixtures had no insulation in them to prevent overheating. These older light fixtures were usually not marked with a maximum wattage for light bulbs. Homeowners could be installing 100 watt bulbs in fixtures that were never meant to have such a high wattage bulb, the wiring above the ceiling fixture could break down, and sometimes the insulation would disintegrate.