What equation is used to estimate the available fault current at the secondary of a service transformer?

The equation used to estimate the available fault current at the secondary of a service transformer is based on the full load amperage (FLA) of the transformer and its impedance percentage (%Z). The correct formula expresses the relationship between these two variables in the context of calculating short-circuit current.

When applying the formula I_SCA_ = (Trans FLA * 100) / (%Z), you are taking the transformer’s full load amperage (Trans FLA) and multiplying it by 100, which allows you to convert the impedance value to a percentage format that is required for the calculation. The division by the percentage impedance (%Z) indicates the impact of the transformer’s impedance on the available fault current. This equation effectively shows how the transformer characteristics influence the maximum fault current that can occur at the transformer's secondary side during a short circuit event.

Understanding this relationship is crucial for electrical safety planning and ensuring that the protective devices and equipment are adequately rated to handle potential fault conditions.