Aluminum is an excellent conductor of electricity and has been used successfully as a varnished magnet wire for many years. It has its own unique properties and, like all wire, is most useful when its unique characteristics are fully utilized. Specified by makers of fluorescent and H.I.D ballasts and other electrical equipment - GE, T&B, Cooper, Advance and Universal Lighting Technologies - for over 30 years, aluminum is the dominant wire in 15-1500 KVA dry-type transformers.
UL and the Arrhenius Curve
Underwriter's Laboratory is generally recognized as the primary electrical safety organization in the U.S. They have been focused on fire prevention and safety since their origins after the Chicago fire in 1892.
U.L. not only recognizes the use of aluminum magnet wire as satisfactory, they rate the varnish insulation system used on the Universal Lighting aluminum wire at 20C higher temperature than they do the equivalent copper magnet wire.
These temperature ratings are based on the Arrhenius curve, which predicts the rate of degradation of a given insulation system based on its survival under specific test conditions. U.L. has used this principle to establish that for this insulation system, every increase of 8.2 degrees Celsius reduces the life of the insulation system by one half. Based on these tests an aluminum ballast coil, run at the same temperature as a copper coil, can be expected to have more than five times the average insulation life of the copper coil.
One of the inherent properties of aluminum is that in the presence of oxygen it quickly forms a very tight oxide skin that is also a good insulator. This adds to the wire varnishes ability to provide good insulation over a long time. Copper, on the other hand, inherently catalyzes the thermal degradation reaction of all organic polymers. In other words, the chemical nature of copper accelerates the thermal breakdown of the insulating varnish over time. This characteristic accentuates the differences between aluminum and copper when they are used as insulated magnet wire in a ballast coil.
This insulating oxide film must be dealt with to terminate aluminum wire successfully. A connection to aluminum wire must be properly plated and crimped (or soldered with a special solder) to be gas-tight. This prevents the formation of aluminum oxide film that could raise the resistance of the joint and cause a problem. Quality suppliers of electrical terminals have a complete line of crimp connectors for aluminum wire that have been used successfully in a variety of applications, including ballast coils, for many years. Of course, these aluminum connections are solely internal - Universal Lighting Technologies still useshigh quality brass terminals and copper leads in all ballast designs.
More wire can be made from a pound of aluminum than a pound of copper because aluminum is less than 1/3 the weight of copper. This is a better use of natural resources and reduces the weight of the ballast. The ballast and the luminaire will be lighter to ship and less prone to shipping damage.
Aluminum's electrical resistivity is higher than gold, silver, or copper. So, although it is still a very good conductor, wire size must be accurately specified. Universal Lighting has found that if the wire size is increased, usually two AWG sizes, coil resistance is the same as if the coil were made with copper wire. However, not all ballast designs have sufficient room for the increased wire size, so some designs must use copper unless they are re-tooled for a larger coil window in the steel frame.
In summary, a properly designed ballast with aluminum wire is generally superior to an equivalent copper-coil ballast. The aluminum ballast is lighter (therefore less costly to ship, easier to mount in a fixture), gives the same electrical performance and losses, and can be expected to give significantly longer ballast life.