What material is typically used for the maximum size conductor in push-in connections?

The correct choice is copper because it is the standard material used for maximum size conductors in push-in connections due to its excellent electrical conductivity, flexibility, and durability. Copper allows for reliable and efficient electrical connections, minimizing the risk of overheating and ensuring optimal performance in electrical systems.

Given the other materials listed, aluminum, while also conductive, is typically used for larger conductors and requires more consideration regarding oxidation and connection techniques. Steel might not provide the required electrical conductivity for reliable push-in connections and is more commonly associated with mechanical structure rather than electrical conductivity. Brass, although it has good conductivity and is often used in connectors and terminals, does not match copper in terms of performance for electrical wiring applications, especially in high-current situations. Hence, copper stands out as the most suitable material for this application.