The metal box of the distribution box, the electrical installation board, and the metal base and casing of the electrical appliances in the box must be grounded. The protective neutral wire should be reliably connected through the terminal board. Correct grounding of services depends upon understanding the definition and role of the grounded conductor. The short answer is two rods at each transformer, 6' apart and 8ft deep. Circuits are grounded to limit excessive voltage from lightning, transient surges, and unintentional contact with higher voltage lines, and to limit the voltage to ground during normal operation.