When calculating available short-circuit current without motor contribution, which multiplier is best used?

When calculating available short-circuit current without considering motor contribution, a multiplier of 4 or 6 is often utilized. This range is generally accepted in industry practices to provide a conservative estimate of the short-circuit current that may occur in an electrical system under fault conditions.

The reason for using a multiplier in this context is to account for the potential contributions to short-circuit currents from various factors in the electrical system, such as transformer impedance and the contributions from other connected equipment, while excluding the dynamic contribution of motors during fault conditions. This helps ensure system protection devices are appropriately rated and configured to handle the short-circuit scenarios that could arise, thus promoting safer operation and preventing equipment damage.

Using a multiplier of 4 or 6 acknowledges a balance between safety concerns and practical considerations, taking into account the foreseeable variations in system behavior during faults. In contrast, higher multipliers might overestimate the calculated short-circuit current, leading to unnecessarily large protective devices or components, increasing costs and complexity in system design. Therefore, this selection provides a practical approach to assess short-circuit current effectively while maintaining safety standards in electrical systems.