Present IEC guidelines are difficult to apply to realistic cases because of the data load, the number of assumptions required and the computational complexity. A new approach is given based on the concept of voltage droop, to be detailed in a companion paper. The benefits of the approach are a simple calculation with minimal data and no required assumptions. It applies to radial or meshed distribution systems where feeders are sufficiently short that line capacitance can be ignored. The approach can be applied at the installation (MV or LV) and the equipment level and can be used to give reference values for equipment emission standards.