Knobs and tube wiring are standard methods of residential electrical installations used during the dawn of house wiring. The method was used from the late 1800s to the beginning of the 1940s to supply power in houses. It consists of copper conductors that run on the ceiling or walls of a house covered in protective insulators or tubes. The system of wires is held by joints and studs drilled into a wall. Cables run from the source to a wiring device which is often protected by a rubber or asphalt-saturated cloth insulator known as friction tape.
To date, knobs and tube wiring are still used in house electrical installations under certain circumstances, as recognized by law. Countries and states have put in an effort to eradicate this ancient method that is considered unsafe for electrical installation. In circumstances requiring the use of knobs and tube wiring, for instance in the industrial or agricultural sector. Due to the costly nature of the installation, it is unlikely to see this installation used in modern houses, however, it still exists in basements or house attics in some homes.
Grounding knobs and tube circuits are unacceptable in some countries like the US that prohibit using the earth as an equipment grounding path. The national code states that the earth shall not be considered as an effective ground-fault current path. In some countries though, grounding is allowed but safety is not put into consideration over this system. Third world country homes still use the ancient system while there exists no government restriction from it.
If you have an ungrounded knob with a tube wiring system, you can safely ground it by attaching a pigtail to the box with a receptacle after splicing it together. Other grounding methods can be done in plastic boxes, fixtures, or switches. Unfortunately, these methods are considered not safe compared to modern ways of grounding causing a ban on it being used in some countries. Grounded wires are often exposed with no electricity running through them hence safe to touch but in case of a power surge, the wire will electrocute the person in contact with them.
In case of lighting or power surge in the knob and tube wiring, it is safe to use if the circuit is grounded. Grounding ensures the safety of your home by preventing short circuits as a result of faulty wires. This will prevent possible fire outbreaks from hot currents preventing a property from potentially damaging. As knobs and tube wires pass near materials that easily catch fire like wood or cloth, it’s important to ground the circuit for the flow of electricity to stay in the wires even in case of a power surge. This backup plan prevents danger caused by electricity faults saving lives or property.
When you have to use this method of electrical installation, grounding it may be a life-saving tip. Electrical surges and short circuits happen unexpectedly, but when they’re grounded, all currents are directed into the earth, preventing materials near the hot current from catching fire.