Electricity as an energy source was discovered in the late 1800s. While some early cutting-edge buildings adopted the technology early on, electricity was still in its infancy. It wasn’t until the 1900s that electricity became more common within buildings.
In the 1920s, the installation and commercialization of electric supplies in buildings increased dramatically. Only 50% of homes in America had electricity installed in 1925 and businesses were still incorporating electricity into buildings. Electrical installations in homes and other buildings become more and more popular in the proceeding years. Today, practically all buildings in America and developed nations have electrical installations.
Electric is now an essential part of modern life and a buildings’ operation. The use of metal (notably copper) to conduct electrical current has generally not changed since electricity was introduced. However, it wasn’t until the 1960s that plastic-covered cables were invented. Before this, cables were often covered with cloth to insulate and protect the conductors.
Aluminium wiring is also a concern with buildings of this age. Within article The Dangers of Aluminum Electrical Wiring we discuss the issues associated with aluminum as a conductor, compared to copper.
In this article we will explain what cloth-covered wiring is, and why it causes problems in buildings.
What is Cloth-Covered Wiring?
Modern electrical cables are covered with plastic (usually polyvinyl chloride (PVC)) insulators over the conductors to protect from shocks, arcing and short circuits. Insulated cables are either run individually within protective conduit; or cable manufacturers group the individual insulated conductors into multiple-conductor cables. The cables are then protected and grouped together with an external outer plastic sheathe.
Plastic is an excellent material for insulating copper as it does not conduct electricity and protects the conductors from air and moisture which can damage the conductors. When electricity was first introduced, plastic in its modern-form had not been invented.
Before plastic-covered wiring and until the early 1960s, cloth-covered wiring was common practice. Conductors were often individually insulated with vulcanized rubber (an early plastic) which was then wrapped with an exterior braided cloth sheath. This is known as cloth-covered wiring.
Why is Cloth-Covered Wiring Dangerous?
While cloth-covered proved effective at the time installation, over the years the rubber perishes and breaks down, and the cloth covering deteriorates.
Deterioration of the rubber can lead to exposure of the conductors which can cause shocks, arcing or short circuits. Eventually this may cause overheating of the electrical systems which may lead to fires.
The National Fire and Protection Association (NFPA) reported that “Home fires involving electrical failure or malfunction caused an estimated average of 440 civilian deaths and 1,250 civilian injuries each year in 2012-2016, as well as an estimated $1.3 billion in direct property damage a year.” A large proportion of these were a direct result of aging and defective electrical wiring and low voltage distribution.
Cloth-covered wiring is also susceptible to damage from rodents and insects, which can chew through the exterior cloth and rubber coverings exposing live conductors.
How is Cloth-Covered Wiring Installed?
Cloth-covered wiring is generally installed as individual conductors and not grouped into multiple-conductor cables like modern cables. Cloth-covered wiring can be found running in conduit, much like modern PVC cabling.
In older buildings in the United States, an alternative method called knob-and-tube (also referred to as K&T) is common (although many original installations have now been removed and rewired using modern methods). The K&T method consists of running individual hot (live) and neutral conductors throughout the building. Cables are supported off ceramic knobs which are fixed to the buildings’ structure and pass through ceramic tubes at walls and structure junction points.
Where electric connections are needed, a small section of the cloth insulation is removed from the main hot and neutral cables, and secondary cables are spliced and wrapped/soldered onto the main cables. Where connections occur, the joints are wrapped with rubber insulation tape (sometimes called “friction tape”).
The K&T method was installed without a ground (earth) wire. Today the installation system is regarded as outdated and does not meet modern building code and electrical installation standards.
Should cloth-covered wiring, or K&T installations be discovered in a building, it is indicative that the wiring system is past its useful life and should be replaced.
Is all Cloth-Covered Wiring Dangerous?
Cloth-covered wiring is a concern. It can be easily found by building owners, electricians and consultants due to its tell-tale woven cloth exterior. However, in certain situations not all cloth-covered wiring is dangerous.
In the 1970s, manufacturers sometimes grouped individual conductors with an exterior braided cloth covering. While this gives the appearance of cloth-covered wiring, this may not be the case. The insulators inside the outer cloth covering may in fact be covered with modern PVC insulation and are grouped together with an exterior cloth sheath. The only way to find out if the insulators are PVC covered is to inspect the wiring at a termination point, i.e. within a receptacle outlet or panelboard.
On some products, cloth covered cable is used as an appliance cord, especially in hard-wearing or vintage-style items. Examples include irons and modern antique-style items such as lamps. The cloth-covered wire can give the impression of older wiring, but this may not be the case. The insulators inside the outer cloth covering may in fact be covered with modern PVC insulation and only be grouped together with a cloth sheath. The PVC connections can be determined at termination points in the appliance or plug.
If in any doubt, consult a professional certified and competent electrician who can recommend whether your cloth covered wiring is dangerous.
What Happens if I Discover Cloth-Covered Wiring?
Cloth-covered wiring, other than the exceptions listed above, is generally a sign that the wiring systems within your building are old and past their useful life. Given the age of the wiring and associated deterioration and risks, it is highly likely that cloth-covered wiring will have to be removed and replaced and either a partial or full rewire will be needed.
If you decide that you need to replace your cloth covered wiring, we suggest you consult with a qualified electrician. In addition to the wiring, you may need to replace junction boxes, receptacles, breakers and possibly ground fault interpreters. The cost to complete this work can range from $6.50 to $12.50 per SF depending on complexity of the work and type, location and size of your building.
If you discover old cloth-covered wiring in your building, proceed with caution. If in poor condition and touched or disturbed, the insulation may be brittle and can easily fall off the wire. This can expose live conductors creating a shock or fire risk. If in any doubt, consult a professional, certified and competent electrician who can advise further.