It is of extreme importance that any amateur realize the incredible and grave danger the electrical circuitry of the modern home poses. It is therefore strongly recommended that only trained and certified technicians perform any kind of electrical work. Many "weekend warriors" in fact only succeed in creating perilous shock or fire hazards when attempting to install additional electrical circuitry. Even simply removing the outlet or switch covers for painting purposes poses a deathly threat. The voltage traveling through home wiring and fixtures can seriously injure, maim, dismember or easily kill!
Most home buyers disfavor discovering a home constructed with aluminum wiring. But most do not know why. The point is that in some cases aluminum wiring is completely safe. In fact, if your home was built or remodeled before the early 90's, the house probably does have aluminum wiring installed in at least some components. If your home was constructed during the copper shortages of the 70's era, most or all of the circuits are wired in aluminum. In some cases, however, the condition of the aluminum wiring can be catastrophically disastrous.
First, aluminum is electrically less conductive. That is to say that it offers more resistance to the passing of electrons. All electrical circuits are resistant to the flow of electrons, most of which is at the electrical appliance doing the "work". The heating elements in an electric oven, for example, are specifically engineered to offer electrical resistance because the direct by-product of electrical resistance is heat. Therefore ideally, it is preferable that conductors (the product designed to carry electrons such as wiring) offer as little resistance as possible. In fact, aside from the common Al-Cu rated breakers, the other components of a electrical circuit are not engineered to compensate for the "excess" heating of aluminum wiring.
The "excess" heat produced from the passing of electrons through aluminum wiring is not itself significant. When heated or cooled, however, aluminum expands and contracts at a greater rate and to a greater degree than copper. Each cycle of heating and cooling, (expansion and contraction) results in mechanical stress at the circuit connectors. The long term, repeated mechanical stress at the connectors then manifests significant loosening. A loose connection, by definition, allows for less surface area contact between the materials being connected, and in turn, ultimately results in significantly hazardous heating. Indeed, poorly crafted aluminum wiring is suspected as the root cause in many residential fires.
Secondly, aluminum tends to corrode more quickly and readily than copper. Corrosion along the length of the wire is not necessarily problematic. But corrosion at the joints and connectors destroys the conductive efficiency from one surface to another. Generally, a metal raised to a higher oxidation state is less receptive to the passing of electrons. And again, the decrease in the permissive surface tension causes significantly hazardous heating.
The above scenarios are common, but are only found in certain circumstances. Problematic corrosion can mitigated with the correct application of a non-flammable anti-oxidant. Electrical connectors are on the market that are approved for use with aluminum, and correction of aluminum faults. Lower gauge aluminum wires do not significantly stress connections because they have multiple strands, allowing for expansion to consume residual volume. And still yet, some wires visually appear to be composed of aluminum, but upon closer inspection it is revealed that the wire is actually aluminum plated.
Electricity, or electrons are not "spent" when the current travels through an appliance. It is in fact the movement of electrons which do the "work." So that the electrons travel into an electrical appliance through the "hot" wire and return through the "neutral" wire. Ground fault interrupters (GFI's or GFCI's) cut off the voltage within a few seconds if they detect an imbalance between the current flowing in the hot conductor and that flowing through the neutral conductor. This imbalance need not be any greater than 0.006 amps to cut off the power within a six seconds (cut-off time is much more rapid when the current difference is greater).
GFI's are wired to do this on the assumption that if the currents are not identical, some of the current is being diverted to "ground" through an unintended path. That path could be through the human body, a shock hazard, or through a faulty appliance, a fire hazard. Contrary to myth, GFI's can detect this imbalance equally well with or without a grounding wire at the receptacle (some circuit analyzers will not trip the GFI without a circuit ground).
Class 8 GFI placement requirements have evolved over the years and their are not any requirements for updating placements in a transfer of ownership of the property. Any remodeling projects which require a city or county issued building permit will require updating the circuitry to current codes and require a subsequent inspection. As of adoption of the 1996 NEC (National Electric Code), GFI protection is currently required for: all kitchen counter receptacles; all garage, grade-level, and below grade receptacles unless dictated for dedicated circuits for permanent appliances (for example, a sump pump or garage freezer); at least one basement receptacle; and all outdoor receptacles, including those more that 6'6" above grade. The NEC also specifies that GFI protected outlets with open-grounding must be provided with a label stating that no equipment ground is present.