Knob and tube wiring still exists in older homes today and it still can be found during New Jersey Home Inspections. Knob and Tube (K&T) was an early residential wiring that was used in homes from the 1880's to the 1940's. It is considered to be obsolete and by some unsafe.
Knob and tube wire is a system of wiring that is installed in open air. The wiring has both hot and neutral connectors. The notable missing wire is the ground. Knob and tube does not have a ground wire. The wiring is protected by an outer sheath that is made from asphalt and then in later years the wiring was protected with a rubber outer sheathing.
The Knob and tube wire is installed through porcelain knobs. These knobs keep the wire from touching combustible surfaces such as wood members for example floor joists or ceiling joists. When the wire has to pass through a piece of wood framing porcelain tubes are used so the wire does not come into contact with the wood or other combustible surface. K&T wire was named for these characteristic knobs and tubes.
The wiring is not inherently unsafe but due to its age and many times improper modifications the wire should be considered for replacement. K&T wire requires air space around it in order to properly dissipate heat. As current moves through the wire, the wire heats up. The big issue here is insulation touching or installed close to the old knob and tube wire. If insulation is present around the K&T wire a significant fire safety hazard will exist.
Another problem with Knob and tube wire is that due to its age the insulation material tends to get brittle and crack. When this happens, the wire is exposed and thus unsafe. If the live electrical conductor is exposed a person can come into contact with it causing a serious electrical shock hazard. Knob and tube wires are also usually undersized for modern electrical applications. Another consideration is that the old wire is not grounded so three prong electrical appliances cannot be safely powered by this ungrounded wiring.
Bar far the biggest issue that NJ Home Inspectors see with knob and tube wire is improper modifications. Due to its age, there has been plenty of time for people to splice, modify or reconfigure the old knob and tube wiring in homes. When Moden Romex or BX is improperly spliced into an old knob and tube circuit a serious fire hazard can exist.
Attempts are usually made in order to help increase the amperage load on the knob and tube circuit to better meet the needs of a modern lifestyle. A problem exists when non-professional electricians make modifications causing serious overload hazards on the old wire. It is very common to find improper splicing of modern wire into the older knob and tube wire which is a fire and shock hazard.
Modifictions are so prevalent that insurance companies will often not underwrite homeowners' insurance when a home has knob and tube wire present. If the home has K&T wire the client should check with their insurance company in order to determine if homeowners insurance will be available and at what price.
If you have knob and tube wire in your home or a home you are considering purchasing the safe way to deal with it is to have it replaced. However, if that is not an option you can consider the following.
If you are contemplating keeping the wire in the home, you should have it professional evaluated by a licensed electrical contractor in order to determine if the system is still safe for use. If you keep the knob and tube do not overload the wiring by operating too many high draw appliances on the knob and tube circuits. Knob and tube wire is not safe to power kitchens and bathrooms. Proper grounded electrical circuits are required in these rooms for safety. If there is any insulation touching or close to knob and tube wire the insulation should be removed and if that is not possible the wire should be replaced.
Home inspectors in New Jersey should be well educated about knob and tube electrical wiring and provide helpful information to their clients regarding this very old wiring.
John Martino
LookSmart Home Inspections
973-407-9621
NJ Home Inspectors Lic # 24GI00058700
5 Preston Ave
East Hanover, NJ 07936
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