What is knob-and-tube wiring and is it safe?
Quick answer: Knob-and-tube is an early wiring method used into the 1940s and sometimes later, recognizable by ceramic knobs and tubes supporting individual cloth-insulated wires. It appears in some of Bloomington's oldest homes. It lacks a ground, the insulation degrades with age, and it can be unsafe when buried in insulation, modified by amateurs, or overloaded by modern demand. An inspector flags any visible knob-and-tube and recommends evaluation by a licensed electrician, as insurers often have concerns about it.
The system was designed for the light electrical loads of its era and has no grounding conductor. Today's appliances and electronics place far heavier demands on circuits, which can overheat aging knob-and-tube wiring.
A particular hazard arises when later insulation is added over knob-and-tube, which the original design assumed would be open to air for cooling. Buried wiring can overheat, and amateur splices into the old system compound the risk.
Because of these concerns, many insurance companies hesitate to cover homes with active knob-and-tube. If your inspection finds it, an electrician can assess what is still in service and recommend replacement of the active runs, which is wise for both safety and insurability.
