You may have bought a home and tried obtain insurance when you realize you may not be able to get home insurance. No insurance-no mortgage. No mortgage-no real estate transaction.
Some insurance companies consider knob and tube wiring unsafe or a significantly higher risk.
They requires two wires (normally a black one and a white one) to create a circuit. With modern wiring, these two wires (along with a ground wire) are bundled together in a single plastic sheathing. Older wiring was installed so that the black wire and the white wire ran separately. It was installed in houses up until about 1950. Knob and tube wiring used protective ceramic tubes placed in the holes to prevent the wire from chafing against the woodwork.
They used more elaborate ceramic knobs to clamp the wire to the structural member. Connections between modern wires are completed within enclosed junction boxes. Knob and tube wiring had visible connections. The wires were spliced and soldered together and then wrapped with electrical tape. Ceramic knobs were used to secure the wires so that anyone inadvertently tugging on the wire would not be tugging on the electrical connection. Modern wiring is typically #14 gauge copper wire and capable of handling 15 amps. Knob and tube wiring is often #12 gauge copper wire and can handle 20 amps. Note: Even though some knob and tube wiring is capable of handling 20 amps, we suggest that it be protected by 15 amp fuses because, in all likelihood, some modern #14 gauge wire may be connected to the older #12 gauge wiring.
The wiring which was installed properly, and has not been abused, can provide many more years of service. The biggest problem with these types of wiring has nothing to do with the original wiring. It has everything to do with what has happened after the fact.
For more information, please visit the Electrical Safety website and search for Flash 09-09-FL