Image by robby-T, used under the CC BY-ND 2.0 license.
Electrical insulation
Electrical wires and cables are insulated to help protect the wires from damage, corrosion and electromagnetic interference. Over time though, this insulation may become brittle or worn, or may be attacked by pests. The breakdown of electrical insulation is a cause of house fires - as well as many other electrical problems. Insulation testing can be done by an electrician using an insulation tester. Insulation is measured in ohms (the unit of resistance - expressed as Ω).
The insulation of a circuit has to be at least 1 megohm (one million ohms). The insulation of house wiring is tested at a high voltage, 500 volts which is more than twice the normal voltage for the circuits.
Old wiring may well have serious insulation problems. Serious problems come about in part through the insulation material becoming brittle, and exposing live copper wire. Continuous operation at high ambient temperature can cause ‘carbonisation’, and that can allow leakage current and cause further breakdown.
Breakdown of wiring insulation is responsible for 30 percent or more of fires caused by electricity in the home. If you are in a house that's more than thirty years old and you haven't done so, you should get an electrician to inspect the condition of the wiring.
Thermal insulation and house wiring
Thermal insulation is a good thing for economic heating and cooling, but is a potential problem for house wiring. Long term overheating of wires buried in insulation can cause the insulation to be degraded, and PVC insulated cables are no exception. If you're getting insulation or wiring installed, check with your installer to make sure there aren't any problems with this.
