Pictured here is knob and tube wiring. This type of wiring can date back as far as the 1880’s and was popular well into the 1940’s to distribute power throughout a home usually for a single receptacle or light fixture. The knobs are the porcelain cylinder like objects pictured toward the middle right of the photo where the conductor is looped and nailed taunt. The tubes, also porcelain, are pictured going through the ceiling joists right below the knobs in the photo. When a conductor was ready to be terminated additional insulation sleeves would be slid over the single conductor (black tubular wires pictured) and installed into a clamp box. This system is obviously tampered with and needed replacement. Some homes today still have this wiring hidden in crawl spaces, attics and in basements. K&T, if it has been tampered with from its original installation; can result in loose and exposed connections that can lead to over-heating, arcing and fires. These systems were never designed to power appliances, air conditioning or heaters. If your home has knob and tube wiring, it should be at minimum inspected and powered only by an arc fault breaker or GFCI combo; but ideally removed and replaced by a professional local electrician ,especially if it has been compromised or utilized by newer systems.