Current limits for different types of motors

4 October 2023

This article provides clarification on determining the maximum allowable inrush current for various motor applications, including single-phase, three-phase and rural single/split-phase loads as per Section 10 of the WASIR.

Single-phase starting currents

Table 5 in Section 10 of the WASIR covers single-phase starting currents. The starting current for metro and major regional areas is limited to 45A. Other locations in the SWIS network are limited to 18A.

Three-phase starting currents

Table 6 in Section 10 of the WASIR covers the requirements for three-phase starting currents. There are three sections, and loads greater than 6kW require a small calculation.

For example, a 10kW motor requires the current to be reduced to 45A as follows: 10kW –  6kW = 4kW,   4kW x 3.2A = 12.8A,   12.8A + 33A = 45A.   

Note: Table 3 in Section 7 states the kW values for starting currents on the Horizon Power network. 

Inrush currents for motors in rural supplies with single/split-phase loads

Table 7 of Section 10 of the WASIR covers these motor types.

240V single-phase motors may be started direct online (DOL).

Provided the inrush current does not exceed the maximum levels in the table below, 480V split-phase motors up to 7.5kW may be started DOL, where the installation is served by a sole use transformer 25kVA or larger.