Primarily in the 1960s and 1970s, many electrical contractors used aluminum wiring instead of copper wiring as a way to save money and lower construction costs. However, a number of electrical fires have been attributed to aluminum wiring. Many building codes have been rewritten to not allow the use of aluminum wire for branch circuit wiring in houses.

Copper vs. Aluminum — The Test Results are in! Tests have demonstrated aluminum wiring has inherent properties that make it more susceptible to fires when it was not installed correctly. Here are some of the problems with using aluminum wiring to conduct electricity. Aluminum does not conduct electricity as well as copper. An aluminum wire generates more heat. Aluminum is more brittle than copper. Wire is more likely to break or crimp if it is brittle. Arcing can occur if a wire breaks or crimps. This can cause very high temperatures inside the wall or ceiling Aluminum is more likely to corrode than copper. Aluminum will oxidize if it comes in contact with moisture. This oxidation removes the pure aluminum and makes the wire thinner. A thinner wire creates more heat when electrical current is running through it. Oxidation also causes the wire to expand, puts pressure on the protective plastic coating on the wire, and can cause the plastic to split. If any of these occur, arcing may result which can cause fires. Aluminum expands and contracts more than copper. This puts additional stress at all connections such as outlets and switches. If these become loose, arcing can occur at these points. If contemplating buying an older home with aluminum wiring or updating a home with aluminum wiring, contact a certified electrician to gain their expertise and opinion regarding the dangers of aluminum wiring.

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Between 1965 and 1973, aluminum wiring was used to install electrical branch circuits in about 1.5 million homes in the United States and Canada. Subsequent fires in some of these homes were attributed to faulty aluminum wire connections. During this period, studies conducted by the National Fire Protection Association, in conjunction with the U.S. Consumer Products Safety Commission, revealed that homes using aluminum wires manufactured before 1972 are 55 times more likely to have one or more electrical connections reach fire hazard condition than homes wired with copper. Aluminum wiring in itself is not dangerous. Aluminum wiring, when properly installed, can be just as safe as copper. But if it has not been installed properly, the connections-where the wires join to the outlets and switches- can present a fire hazard.

How to Tell The wiring that is of concern involves the circuit wiring to your outlets and light switches, and to appliances that us 115 volt current, such as furnace and washing machine. It is a single-strand, solid aluminum wire, silver in color as opposed to the characteristic copper wiring color. Most homes of any vintage employ some aluminum wiring. Often service entrance cables from the street that run to the distribution panel and major appliance circuits (220v) are aluminum. The safety concerns are not with the cables, but rather with branch circuit connections involving the lighting and other 115 v circuits. The Problem Most problems arise with solid aluminum wire, sizes #10 and #12 gauge. These problems concern the ends, or terminations, of the aluminum wire, where they connect under the bonding screws. If the connections are improperly installed, there is a potential for intermittent, hot connections where the wires join to the outlets and switches. Again, the problem is with the connections, and not with the wiring itself. The main difficulty with connections using aluminum wiring is a phenomenon known as cold creep. Aluminums coefficient of expansion (how much it expands when electrical current passes through it) is higher than coppers. Simply put, when aluminum wiring warms up, it expands more than copper does, and when it cools down, it contracts more than copper does. This expansion and contraction, over time, will allow for loosening at the connections. Also aluminum wire needs to be larger than copper to carry the same amount of electricity. Because the wires are thicker, you cannot get the same tightness at the connections. Therefore, they may loosen more quickly. To make the problem worse, all metals oxidize or corrode in an oxygen environment. Copper oxidation forms as a conductor, while aluminum develops as a resistor. This resistance causes heat. Oxidation accelerates when two unlike metals are in contact with each other. This may be part of the source of increased resistance when aluminum wire joins to outlets or switches intended for copper. Eventually the wire may start getting very hot, melt the insulation or fixture its attached to, and possibly even cause a fire. Evaluation of Your Electrical System As mentioned above, aluminum wiring can be just as safe as copper when properly installed. Denver’s Building Department has always maintained-including during the years 1965 to 1977, when aluminum wiring was being installed nationwide- a force of electrical inspectors who themselves are licensed electricians and have worked diligently to ensure that all installations comply with local and national standards. Many of the incidents publicized from other parts of the country simply don’t occur here. Still, any potential electrical problem is a potentially serious problem.

There are several warning signs to look for that would suggest the possibility of connection problems. They are:
– Sparks emanating from outlets
– Warm-to-touch cover plates on outlets and switches
– Smoke coming from outlets, junction boxes or switches
– Lights that flicker for no apparent reason
– Melted insulation (plastic) at the connections
– Smell of burning plastic at outlets
– Light bulbs that burn out quickly, or shine unusually bright
– Blown fuses or tripped breakers for no apparent reason
– The size of your television picture shrinks

Making Sure Its Safe
If you are experiencing one or more of the above connection problems, or are otherwise concerned, we suggest that you hire a licensed electrician to check over the wiring for the following:
1. Outlets and switches directly attached to aluminum wiring shall be listed for that purpose. The device will be stamped with AL/CU or CO/ALR. The latter supersedes the former, but both are safe. These fixtures are somewhat more expensive than the ordinary ones.
2. Wire should be properly connected (wrapped at least way around the screw in a clockwise direction). Connections should be tight. While repeated tightening of the screws can make the problem worse, during the inspection it would pay off to have the electrician snug up each connection.
3. Push-in terminals (terminals where the connecting wire is pushed into a slot rather than wound around a screw) are an extreme hazard with aluminum wire. Any connections using push-in terminals should be redone with the proper screw connections immediately. 4. There should be no signs of overheating darkened connections, melted insulation, or baked outlets or switches. Any such damage should be repaired.
5. Connections between aluminum and copper wire need to be handled specially. Current Denver City Ordinance requires that the connections used must be specially marked for connecting aluminum to copper. The National Electrical Code requires that the wire be a connected together using special crimp device, with antioxidant grease (see Repair Options, over).
6. National Electrical Code, Sections 110-114 and 310-314 address electrical conductors of dissimilar metals and prohibit the use of unlisted twist-on connectors for connection of copper and aluminum wiring.

A Final Caution The United States Fire Administration reports that annually, of the nearly 800,000 residential fire nationwide, approximately 75,000 began in the homes electrical distribution system that is, in the circuit wiring, receptacles, switches, cords and plugs. When a part of this network fails or is misused, a fire may result. Many of these fires were attributed to old technology aluminum branch circuit wiring. Of the fires involving old technology aluminum branch circuit wiring, 75 percent of the incidents involved receptacles, 12 percent involved panel equipment terminals, and 10 percent involved twist-on connections. Fire investigators, including those of the Denver Fire Departments Fire Prevention and Investigation Division, determined that old technology aluminum-wired receptacles and twist-on connectors, when used with aluminum wire, were failure prone, even when installed carefully in accordance with the manufacturers instructions. Leave aluminum wiring safety improvements to licensed electrical contractors. Denvor Building Department electrical inspectors will monitor work done under City permit. Any time you suspect unusual heat or smoke generated from the electrical system in your house, do not hesitate to call 911 and request a Fire Company to respond and evaluate conditions. The safety of your family is of primary importance.

This article by the Denver Fire Department is brought to you by Napoleon Home Inspections – The Barrie Home Inspector