Aluminum conductors provide an economical alternative to copper and have been used for many years in various types of insulated wire and cable.

Aluminum conductors used today in building wire and service cables are more than likely manufactured from an aluminum alloy known as an ACM alloy. ACM stands for Aluminum Conductor Material. ACM alloys are in the Aluminum Association’s 8000 series of alloys and are recognized for use in various wire and cable products by standards organizations such as Underwriters Laboratories and the Canadian Standards Association.

ACM alloys were developed by aluminum producers in response to problems experienced with aluminum conductor building wire in the late 1960’s / early 1970’s. These were mainly connection problems associated with the use of aluminum alloy 1350 which was, and in some products still is, the alloy used for electrical wire and cable. Connections were made using devices that were not designed for use with alloy 1350 conductors and because of this there was overheating at connection points and even fires that were attributed to the use of aluminum conductor cable. These were mostly with solid #12 and #10 AWG conductors used in residential branch circuit wiring. Because of a property called cold flow that was not considered in the design of earlier splicing and terminating devices, problems were experienced that gave aluminum conductors a bad reputation. To a certain extent that reputation exists even to today. Aluminum alloy 1350 conductors were and still are perfectly acceptable if proper splicing and terminating devices as well as good installation practices are used.

In this case cold flow is the property of an aluminum conductor to flow away from the pressure exerted by a terminating device on that conductor. In an effort to overcome this tendency and in that way improve the image of aluminum conductors, the aluminum producers developed the ACM family of alloys that are now in the 8000 series of alloys. They did this by adding other elements such as iron, magnesium and copper to what was basically alloy 1350. By adding these alloying elements cold flow was greatly reduced as well as the degree to which the conductor surface oxidizes. This improved the performance of these 8000 series alloys over that of 1350.

Chemical physical and electrical properties of the 8000 series alloys are detailed in ASTM Standard B 800. There are several ASTM standards for alloy 1350 drawing stock (rod) and conductors. The physical, chemical, and electrical properties of alloy 1350 rod is detailed in ASTM Standard B 233.

Conductors are made by taking rod and drawing it down to form a wire. Drawing is really a process where the rod is stretched by pulling it through a series of dies that gradually reduces it’s diameter to what is required. This wire can then be used on it’s own as what we call a solid conductor or stranded ( twisted ) together with other wires to form what we call a stranded conductor. Drawing is a mechanical process that work hardens the metal whether it’s copper or aluminum. In order to make the completed conductor softer and therefore easier to install it must be heat treated in some way. This can be done be heat treating the individual wires ( usually called annealing ) before stranding or by heat treating the completed conductor before insulating. With alloy 8000 conductors the heat treating softens the conductor but it also increases the metal’s conductivity to approximately 61% IACS ( pure copper being 100 % ). 61 % IACS minimum conductivity is the U.L. and C.S.A. requirement.

Over time 8000 series conductors became accepted for use in larger and larger stranded conductors by both the standards writing organizations and users. Solid aluminum conductors are still not used to any great extent in building wire.

Terminations and splices must still be made using approved devices and installation practices. If these are followed reliable connections are ensured and the problems experienced with the use of alloy 1350 conductors many years ago will be avoided.

Nexans uses alloy 8030 as it’s ACM conductor material. Our raw material specifications for purchasing both rod and completed bare conductor detail that the alloy be 8030. This is exactly the same alloy as Alcan call NUAL in Canada and Stabiloy in the U.S.

By : D.S. Reith, C.E.T. – Applications Specialist

August 23, 2001