According to NEC Article 250, both the neutral and ground wires must be connected only in the main panel or at the first service disconnect. They should never be connected together downstream of the service equipment, such as in subpanels or other parts of the circuits. This practice is essential. Primary distribution systems consist of feeders that deliver power from distribution substations to distribution transformers. Many feeders leave substation in a concrete ducts and are routed to a nearby pole. Proper grounding and bonding of this secondary panel are necessary safety. For a Single Phase Transformer with dual 120V secondaries, to derive a 240/120V system with a neutral, connect terminals X2+X3, which will then be the neutral terminal. 240V will be available between X1 and X4.
