Sounds more like a punch line than an electrical system right? Knob-and-tube wiring (sometimes abbreviated K&T) is an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the early 1940s. Many homes in older neighborhoods around Central Ohio are still relying on wiring that predates the Model-T Ford. It has no ground wire and thus cannot service any three-pronged appliances. This greatly increases the risk to appliances from overcurrent and is a source of many electrical fires. The NEC requires that this wiring be entirely exposed and cannot be covered by any insulation. This essentially means that most attics with K&T wiring cannot be insulated due to fire risks. While there is no mandate that this be replaced across the board it has been banned for many decades. Older homes are spectacular and offer features and floor plans that are highly desirable and only found in these old treasures. That being said it is important that you know exactly what you are getting BEFORE you buy.