Why is Knob and Tube considered so dangerous? Other than being old with the potential for brittle wires and other than modifications, improper splices, etc. If the insulation is brittle it can be a big hazard where exposed (basement, crawl space, etc.) With K&T theres no risk of shorting in the walls since the wires are seperated. Theres a risk of overheating if installed in insulation, is this because its a single wire and no return current running next to it to cancel out the induction, so the magnetic field will cause heating? If there is original un-altered K&T, wire insulation still decent, serving only light duty loads (heavy load areas re-wired) is there any safety risk leaving it?