Although the actual wire used may be no different from that used today for the most part, it consists of only a hot (black) and neutral (white) wire with no ground wire. Both wires must run separately to fixtures as opposed to those used now which are contained within one plastic sheathing.
Knob and tube wiring can be safe and functional. Hire a qualified electrician to inspect the wiring to determine its safety. With proper documentation from a certified electrician many insurance companies will readily insure your home. While I have safely owned many homes with knob and tube, there are some issues to be concerned about, such as, the fact that there is no ground wire, which may be an issue for today’s lifestyle, high electricity usage and technology. Also, there are potential fire hazards with the break down of the insulation around the knob and tube wiring that comes with age, and should the black and white wires make contact.
In recent years some home insurance companies have begun to refuse to insure homes with knob and tube wiring, however, there are companies that continue to offer regular priced policies for homes with knob and tube, and others who ask a premium for this insurance. If you have any qualms about the safety of your knob and tube wiring, you can hire an electrician to update your home wiring. Be sure to get a quote, and expect to pay more to update a two- or three-story home, than you would for a bungalow. Keep the receipt to show prospective buyers when it comes time to sell.
If you intend to purchase a home in an area where knob and tube wiring was used then ask your realtor for advice on securing insurance and peace of mind. Your realtor may recommend the use of a condition in your offer to purchase that allows you the buyer to satisfy yourself that the house is insurable. That way you won’t be stuck struggling to find insurance right before closing.
Electrical Dangers in Homes With Knob and Tube Wiring
A common danger relating to knob and tube wiring is the use of electrical devices requiring grounding that are connected to "ungrounded, 3-prong receptacles" (found in virtually all homes examined). This situation, the "lack of ground" can easily be remedied with the replacement of the ungrounded 3-prong receptacles with GFCI receptacles (or GFCI protection at the panel). This is an excellent solution that in my opinion provides equal if not better ground protection than standard 3-prong grounded receptacles.
In summary, electrical hazards have been found both in homes with and without knob and tube wiring, but the hazards have by-in large not been related to the knob and tube wiring itself. Homes with significant hazards have by-in-large been related to (a) the age of the house (the number of years where Handyman tampering could have occurred), (b) the application of the house (secondary suite or not), and proximity of trees to the service supply conductors. A comprehensive electrical inspection by qualified personnel is the only sure way to identify if and where there are electrical hazards.
BCTQ Electrician, Field Safety Representative (Electrical) and owner PowerCheck