What is the minimum size of a copper equipment grounding conductor required for a 20-amp lighting circuit?

The minimum size of a copper equipment grounding conductor required for a 20-amp lighting circuit is indeed 12 AWG. This size is grounded in the National Electrical Code (NEC), which outlines the requirements for grounding conductors in various applications to ensure safety and mitigate the risk of electrical faults.

Using a 12 AWG copper wire ensures that the conductor can handle the potential fault current effectively and can safely carry any fault current back to the source, which is critical for the proper operation of protection devices like circuit breakers or fuses. Grounding conductors serve to reduce the risk of electric shock and ensure that electrical equipment functions safely under fault conditions.

For circuits with different amperage ratings, the required size of the grounding conductor may vary, which is why it's important to refer to the specific requirements set forth by the NEC. In this case, the selection of 12 AWG for a 20-amp circuit reflects both compliance with safety regulations and practical application for effectively grounding the circuit.