Apparently about half of it went for electrical purposes

Aside from telephone, telegraph, and various power distribution lines which gobbled up copper, you also had massive amounts of wiring going into businesses, and various electrical fixtures and fittings.

The high cost of copper encouraged the development and use of aluminum wire in long distance power transmission lines. Pacific Gas and Electric was a common user of aluminum transmission lines for cost saving purposes.

As an aside, I have a high voltage power insulator that once served a Michigan copper mine, which was built around 1906, and carried 20,000 volts.