Where must an additional grounding connection be made when the utility transformer is outside the building?

An additional grounding connection must be made at the transformer because it is crucial for ensuring the electrical system is safely grounded at the point where the electrical service enters the building. This connection helps to mitigate the risk of electrical faults, lightning strikes, or other disturbances that could lead to electrical shocks or equipment damage.

By grounding at the transformer, you are establishing a solid reference point for the electrical system, which helps to limit overvoltage conditions and provides a path for fault currents to safely dissipate. This is particularly important when the transformer is located outside the building, as it ensures that the ground potential is maintained consistently from the transformer through to the service panel and throughout the electrical system within the building.

Other options may not establish the necessary grounding consistency or may not adhere to the requirements outlined in electrical codes, which call for grounding at the utility transformer as an essential safety measure.