Final answer:
The smallest size copper grounding electrode wire for a separately derived transformer system with #1 AWG copper secondary wires is #8 AWG.
Step-by-step explanation:
The smallest size copper grounding electrode wire for a separately derived transformer system with #1 AWG copper secondary wires would be #8 AWG.
The American Wire Gauge (AWG) system is commonly used to measure the diameter of wires, where a higher gauge number indicates a smaller diameter. In this system, #8 AWG corresponds to a larger diameter than #10 AWG, #6 AWG, and #4 AWG, making it the smallest size copper grounding electrode wire for this system.