Solid Conductor Aluminum Wiring
Small, solid conductor aluminum wiring, such as 10 gauge, rated 20 amps and 12 gauge rated 15 amps, was used from 1965 to 1974. In 1975, the NEC prohibited the use of solid conductor aluminum wiring.
The main concern with small gauge, solid conductor aluminum wiring is its expansion characteristics when heated. If the wire is in a situation where the amount of current that is being drawn does not heat the wire, there will be no typical aluminum wire related concerns (i.e., if an aluminum wire circuit only serves a lamp and a TV, it will not draw enough current to cause expansion problems). A 15-amp circuit that is serving a lamp and a TV will have a maximum load of only about 3 or 4 amps. This is not nearly enough to cause aluminum wire concerns due to heat.
To determine how much current a circuit is drawing, divide the wattage rating of the lighting and or appliances on the circuit and divide by the voltage. Watts = Amps X Volts so a 100 watt light bulb divided by 120 volts equals .8 amps.
When almost anything is heated, expansion will occur. Materials of different densities will expand at different rates. When an aluminum wire is attached to a steel alloy contact with a similar steel screw, and the contact, screw and wire is heated by the current moving through the circuit, everything expands. During this process, the density of the steel will tend to distort the aluminum wire. When the contact cools, the steel alloy will return to its original size, while the aluminum, which was distorted, will not.
When aluminum is exposed to air, a film of aluminum oxide forms on the metal's surface. The oxide formation causes the wire to loosen under the mounting screws. When the screws are worked loose, the oxidation of the aluminum wire under the screws heat and create a fire hazard.
When there is enough distortion, the aluminum wire will become loose at the contact. It may not appear loose, because it may not come off, as you would expect from a loose wire. The loose aluminum wire may function with micro arcing, which will cause more heat at the contact and make the problem worse. The additional heat causes stress on the wire, and may cause a slight fracture in the run of the wire about 1/8 inch from the contact. This fracture causes additional micro arcing and even more heat. Fractures occur at this point because this is the point of maximum temperature difference or change. When multiple arcing occurs, the potential for excessive heat and possibly a fire may be present.
The apparent solution to the problem would be to remove the aluminum wire from the steel alloy contacts. The original suggestion was to pigtail the aluminum wire with a piece of copper wire and to attach the copper wire onto the steel contact. This would have been acceptable, except for the fact that the aluminum and copper, being dissimilar, corrode due to oxidation when they are in contact with each other.
To help eliminate the problems and concerns, device manufacturers developed switches and outlets designed to receive copper or aluminum. These devices were called co/al devices, however, they were not as effective as the manufacturers had anticipated, and were revised. The revised devices are called co/alr, the "r" meaning revised.
With the co/alr devices, the switch and outlet concerns were addressed, however, there is still a concern with fixtures that are wired directly, such as a chandelier. In most cases, and assuming they are wired correctly and the loads are properly calculated, there should be no problems, because the amount of heat generated by these fixtures is not enough to stress or overload the wire. The concerns are related to situations that are unknown or where the wiring or calculations are incorrect.
AMP Corporation designed a wire crimping tool and system that will provide dependable results with aluminum to copper connections. The crimp is designed to ensure that air does not come between the aluminum and copper. After the connection is crimped, it is covered with a sleeve, which is shrunk around the connection. This process minimizes oxidation at the contact. This is the only system that the Consumer Product Safety Commission (CPSC) has accepted. 1. The CPSC does not recognize any other system or correction as acceptable. This creates legal concerns for anyone who may recommend a different solution. 2. AMP Corporation does not sell the crimping tool; they have patents pending and only allow users to lease the equipment. This limits access for residential or small work, because it is difficult to justify leasing costs for one house. 3. The number of "qualified" electricians that have gone through the AMP training creates further limitations. There are very few electricians in the country that have gone through the training, and most are commercial electricians. Based on this situation, we as home inspectors cannot recommend this as a solution, because most of our clients will not be able to find a qualified electrician in their area. 4. Our posture is to explain the aluminum wire situation so that our client understands the concerns, and recommend a licensed electrician to determine the best action.
The NEC and most jurisdictions recognize twister wire nuts and co-alr device usage. The CPSC has not required the removal of the other two methods from the marketplace. This would suggest that there is insufficient research to ban the use of these products.
ASHI and NAHI standards, as well as the ERC inspection guide require inspectors to report the presence of solid conductor aluminum wire.
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