Knob-and-tube (K&T) wiring was a standard method of electrical wiring and common in North America from about 1880 to the 1940s. Problems with K&T wiring arise due to age, corrosion and improper modifications as today's home owners often have an increased need for more amperage that will make electrical upgrades necessary. Problems with K&T can arise as it lacks a grounding conductor (ground conductors reduce the chance of electrical fire and damage to sensitive equipment) and oftentime the insulation fabric that envelopes the wiring is a fire hazard and also tends to stretch and sag over time. But oftentimes the owners of historic homes try to preserve the historic value of their building in which case the continued use of the original K&T wiring should be accompanied by frequent maintenance and inspections.

Aluminum wiring was commonly installed by homebuilders from the 1960s to mid-70s when copper prices skyrocketed during the Vietnam War. Aluminum wiring was an available and cost-saving alternative and when installed properly, aluminum wiring will not pose a hazard. Aluminum wiring is often used today for feeders and large appliances. Problems with Aluminum wiring arise when it is not properly installed, when damaged, or when corrosion occurs. Aluminum must be terminated with crimp sleeves, lugs, and screw terminals. In addition, the wiring must be treated with an oxide inhibitor. The terminals and screws that were used in the 1960s are often corroded today. And, because electrical fixtures and appliances have copper wiring, when connected to aluminum wiring with its expansion and contraction rate being different from copper, the two metals can cause electrical problems when not properly terminated/connected. All wiring heats and expands when electricity passes through. When electricity passes through wire, aluminum wiring expands considerably more than copper wiring. With age, the wire can become loose at the connection from years of expanding and contracting. This is called creeping. Once the wire has become loose at the connection, electricity may arc or spark between the gap. The arcing may cause a house fire. Many insurance companies will not insure homes with aluminum wiring.