Few Aspects of Copper versus Aluminium

Conductor connections and terminations

The constructions of aluminum wire and terminals have both been revised from past years. At one time the conductor was nearly pure aluminum, now they are all much stronger 8000 series alloys, with physical characteristics similar to copper.

The wire terminations also have much more severe UL test requirements, resulting in reliable long-term connections when installed in accordance with instructions. There is a common misconception that only compression (crimp) lugs should be used with aluminum cables, but this is not true.

The terminals on molded case circuit breakers are typically plated aluminum alloy with mechanical setscrews, listed for use with either aluminum or copper conductors.

These lugs rated ALCU alleviate the need for more expensive compression connectors and the more laborious installations for these connectors.

It is more common to have compact stranding of aluminum wire than copper, which can reduce the conduit upsizing required. Even though physically larger the aluminum wire is lighter and easier to handle than the equivalent copper conductor. In
most cases the same lug can accommodate either aluminum or copper and has adequate wire range.

Any lug marked ALCU is suitable for use with either conductor. Another factor with the use of aluminum wiring for the supply or load from a piece of the electrical equipment is the size of the conduits. The use of aluminum conductors will result in either larger conductor size or more quantity of conductors. Either way, more or larger conduits will be utilized.

A design trend is always toward equipment with smaller footprints. Cost of the space in the structures housing the equipment is constantly increasing.

However in many cases there might not be physical space in the equipment for the termination of the conduits using aluminum conductors while there is adequate space for the quantity and size of the conduits for the copper conductors.

Plating and environmental concerns

Both Al and Cu will oxidize when exposed to the atmosphere. Oxides, chlorides, or sulfides of the base metal are much more conductive for copper than aluminum. For a low resistance aluminum joint, the aluminum bar conductors must be plated to minimize oxidation.

Concern over the Al oxidation away from the joint is not an issue and will act to protect the conductor from further corrosion in most environments. Aluminum bus conductors depend upon the plating for the integrity of the electrical connection.

The presence of hydrogen sulfide (H2S) in the atmosphere is of main concern for base metal Cu and silver plating. Both corrode heavily in a relatively low concentration of H2S and most intensely in locations usually having an elevated temperature while the equipment is energized. Two processes are active at the same time, general corrosion of the silver and creep corrosion of Cu. Silver plating is widely used on contacts and other conductive parts in electrical equipment due to its superior conductivity, abrasion resistance and longevity.

Hydrogen sulfide is usually present at chemical plants, oil refineries, steel mills, pulp and paper mills, and wastewater treatment facilities.

In a H2S environment metal filaments (whiskers) start to grow as soon as a thick enough layer of silver sulfide has been formed. This silver corrosion results in a high resistance producing more heat, which further stimulates tarnishing and growth of whiskers. This process if allowed to continue leads to failure due to over heating or short circuit.

Tin plating displays good environmental protection and is a practical solution to the H2S corrosion problem of copper and silver-plated copper.

Cost comparison

The cost difference between copper and aluminum varies with the fluctuating cost of the base metals on the commodities market. However this cost difference is many times the deciding factor when a customer is considering aluminum conductors in their equipment.

All of the references on the cost differences are based on the effect that the current commodities market has on the components into electrical equipment.

The percentage difference in the cost between aluminum and copper also varies as the percentage that the conductor is a component of the overall equipment.

A contrasting example of the conductor being a large percentage of the overall assembly is with busway. The larger the amperage of the busway, the greater the base conductor is to the percentage of the overall equipment.

An example would be comparing 3 phase, 4 wire busway at 1000A to the same busway at 4000A. At 1000A, the adder to go from aluminum to copper would be approximately 50%, but at 4000A, the adder for copper over aluminum is almost 100%.

Panelboards both distribution and lighting class can have a copper to aluminum price differential anywhere between 10-50%. This varies as explained above with the overall price of the breakers and other components installed in the panelboards. Switchboards on average will have a 25-30% premium for copper bus over aluminum bus.

With respect to percentage of conductor content within the equipment, transformers have a higher percentage of the conductor than a panelboard, but much less than busway.

Currently electrical equipment with aluminum conductors designed to perform identical to the same equipment with copper conductors will provide a dollars savings to the end user.

Reference // A comarison of aluminium vs. copper as used in electrical equipment – GE, Larry Pryor, Rick Schlobohm and Bill Brownell,