Present IEC reports (e.g. IEC 61000-3-13 or IEC 61000-3-14) provide a simplified assessment rule based on the ratio of the single-phase equivalent power Sui of an unbalanced customer installation and the short-circuit power Ssc at the point of connection. However, the calculation of the unbalanced power Sui is not clearly defined in the documents, but is crucial for the proper application. This paper provides a general definition to this power equivalent for a customer installation which defines its contribution to voltage unbalance at the point of connection. This definition covers both consuming and generating equipment and can be applied for planning purposes and to assess unbalance of customer installations in operation by measurements.