Vladimir said:
Horses for courses Vlad. Belden clearly have an axe to grind here, but to be fair the cat 5 spec does specifically mention solid copper conductors. I wouldn't use CCA with punchdown insulation displacement connectors as the copper sheath is pierced. It is also more fragile than solid copper cable.
If weight was a major concern however, or if the design spec called for minimum price, then CCA might make sense. As mentioned above, I wouldn't use CCA for hifi.
I recall reading that aluminium is used for loudspeaker voice coils as weight is the constraint, not size.