Copper conductor wires and cables are easier to install as these can be bent, twisted, tightened and pulled without stretching or breaking
Wires and cables need to be flexible as they are required to be installed in containment systems such as ducts and channels along physical routes that curve and bend repeatedly, sometimes by as much as 90 degrees.
The International Electrotechnical Commission has defined four classes of conductors graded according to their flexibility in the IEC 60228 standard:
− Classes 1 & 2 : solid / stranded conductors for fixed installations respectively
− Classes 5 & 6 : flexible conductors for mobile as well as fixed installations and appliances
For classes 1 & 2, both copper and aluminium conductors are permitted. The minimum size for aluminium conductors and strands is 10 mm2 making these inherently stiff. By comparison, a minimum of 0.5 mm2 is allowed for copper conductors, thus enabling multiple strands to be paralleled for enhanced flexibility.
Further, the limiting internal bending radii for copper and aluminium conductor cables are broadly similar and for comparable cable types are likely to be not less than 6-10 times the respective cable overall diameters, depending on cable construction, with aluminium usually having larger bending radii than copper. Since copper conductor cables have a lower relative cross sectional area for the same ampacity due to copper’s superior conductivity, their flexibility is further enhanced by the smaller diameter.
This inherent stiffness and larger bending radii (for the same ampacity) of aluminium conductor cables impacts the installation process in many ways. A physically larger space is required to achieve the bend resulting in larger containment systems or less headroom in switchgear panels. This can be a problem in buildings where other utilities such as HVAC compete for the same void space. Further, cables can become “set” during installation if these are bent with a shorter radius than the permitted minimum , resulting in kinks in the cable that are difficult if not impossible to remove, which remain as potential weaknesses or hot spots if the cable is subsequently straightened during installation.
Conversely, it is possible to install more copper cables into a given containment size, providing more options for future modifications or expansion.
For classes 5 & 6 (flexible cables) , only copper conductors are allowed to be used by IEC 60228, underscoring copper’s inherent flexibility. Aluminium usage is not permitted.
- International Electrotechnical Commission, IEC 60228