Knob & Tube Wiring: 1800s–1930s

Knob and tube wiring was designed as an open air system that used ceramic knobs to separate wires from combustible framing. These suspended wires were directed through ceramic tubes to prevent contact with the wood framing and starting a fire. Today, knob and tube wiring is considered a fire hazard because it is not a grounded system, and is more susceptible to damage from aging and faulty renovations.

Aluminum Wiring: 1960s through 1970s

As the price of copper soared in the 1960s, it became commonplace for home electrical wires to be made using aluminum instead of copper. It is estimated that nearly two million homes were wired with aluminum between 1962 and 1972.

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Grounded Electrical Systems: 1940s through Present

Electricity always seeks to return to its source and complete a continuous circuit. A typical circuit in your home has two conductors: hot and neutral. Electricity travels from the service panel to home appliances through the hot conductor, and returns the current to the main service panel through the neutral conductor. A third or “grounding” wire is also connected to all outlets and metal boxes in your home.

This critical safety feature is designed to greatly reduce your chance of shock or electrocution should a short circuit occur. Grounding wires are connected directly to the earth through a metal grounding rod or a cold water pipe. Should a short circuit or an overload occur, any extra electricity will find its way along the grounding wire to the earth.