Electrical connections made with copper are stronger, more corrosion resistant, less susceptible to cold flow and thermal influences and therefore more reliable
There are four main mechanisms by which the choice of conductor material affects electrical connections - Oxidation, Galvanic action, Cold flow / Creep and Thermal expansion.
Oxidation: When exposed to air at connections and terminations, the surfaces of both copper and aluminium form thin oxide, sulfide and inorganic films which reduce the metal-to-metal contact and effectively increase the contact resistance. The contact temperature rises, and if this is excessive, the connection deteriorates over time leading to overheating and ultimate failure. Where copper scores is that its oxides are soft and electrically conductive whereas those of aluminium are hard, tenacious and effective electrical insulants. As a result, in contrast to aluminium, connections and terminations with copper seldom overheat and do not require surface preparation or the use of oxide-inhibiting compounds.
Galvanic action: When two dissimilar metals such as copper and aluminium come in physical contact in the presence of an electrolyte such as moisture, aluminium as the less noble metal loses material through electrolytic action. The connection deteriorates in two ways – electrically, through a reduction in the contact surface area, and mechanically, through the severe corrosion of the aluminium connector. Therefore, aluminium conductors require a number of jointing techniques dependent on the materials typically used in equipment and accessories such as outlets, plugs and breakers, such as the use of contact sealants, bi-metal terminations or special equipment. By contrast, copper remains unaffected by galvanic corrosion when connected to these less noble metals and alloys.
Cold flow / Creep: High contact pressures are applied on the conductor at mechanical joints and terminations in order to make a good connection and this causes the conductor metal to “flow” away. This effect is pronounced with aluminium conductors but significantly lower for copper due to its greater hardness. Similarly, ”creep” is the plastic deformation of metal conductors that occurs when these are subjected to an external pulling force (stress) and depends on the stress level, its duration and the temperature. Both cold flow and creep lead to a reduction in contact pressure, increased joint resistance and overheating. Aluminium creeps more, faster, and at lower temperatures than copper.
Thermal expansion : When heated by load current, copper to copper, copper to brass or copper to plated steel terminations, tend not to loosen the connection due to the relatively similar rates of thermal expansion, thus remaining secure throughout the installation life.
However, with aluminium conductors in similar terminations, the relatively high difference in thermal expansion can result in loosened terminations over time. The contact resistance increases progressively leading to overheating, arcing and potential fire risks.
Thus electrical connections made with copper are strong, reliable and long-lasting.
- Copper in Electrical Contacts book, ECI publication no. Cu0169, July 2015
- Reliability of power connections, BRAUNOVIC Milenko, Journal of Zhejiang University SCIENCE A,ISSN 1009-3095 (Print); ISSN 1862-1775 (Online), January 2007
- CONNECTABILITY TESTING OF COPPER AND ALUMINUM WIRING, PHASE 2: Current Cycling Tests – Mechanical Connectors - POWERTECH LABS INC. Report #: PL-00236-REP1 , 27 June 2014. https://www.youtube.com/watch?v=ninqsZihz7g