Load current basics in Australian electrical work
How Australian load-current checks use power, voltage, phase arrangement and power factor before cable or switchboard review.
What load current means
Load current is the current associated with an electrical load. It may come from a nameplate, a measurement, a design schedule or a calculation from power, voltage, phase arrangement and power factor.
In Australian 230/400 V a.c. work, the phase basis matters. A single-phase active-to-neutral load is not calculated the same way as a balanced three-phase line-to-line load.
Formula basis to keep visible
For a simple single-phase real-power estimate, the relationship is commonly read as I = P / (V x pf). For apparent power, use I = S / V.
For a balanced three-phase real-power estimate, the relationship is commonly read as I = P / (sqrt(3) x VLL x pf). For apparent power, use I = S / (sqrt(3) x VLL). A three-phase current result is normally line current, not the sum of three lines.
| Input basis | Keep beside the current | Why it matters |
|---|---|---|
| Nameplate current | Equipment label, duty, phase and source. | Shows the current came from product data rather than a calculation. |
| kW or W conversion | Voltage, phase arrangement and PF where used. | Prevents single-phase and three-phase values from being confused. |
| kVA or VA conversion | Voltage and phase arrangement. | Keeps apparent-power current distinct from real-power current. |
| Measured current | Measurement condition and date where available. | Helps separate site data from design assumptions. |
Worked current examples
At unity power factor, a 10 kW load on a 230 V single-phase basis is about 10000 / 230 = 43.5 A. The same 10 kW on a balanced 400 V three-phase basis is about 10000 / (sqrt(3) x 400) = 14.4 A per line.
Those examples are reading aids, not fixed answers. A real check still needs the entered voltage, phase arrangement, load type, power factor where relevant and the source of the load value.
| Situation | Wording to keep visible | Better next check |
|---|---|---|
| Single-phase final circuit | kW or VA, 230 V basis, active-neutral context and PF where used. | Load-current calculator. |
| Balanced three-phase load | kW or kVA, 400 V line-to-line basis and line current. | Load-current calculator in three-phase mode. |
| Submain or cable follow-up | Current value, source, cable route and conductor data. | Cable-size or voltage-drop calculator once cable inputs are ready. |
| Switchboard schedule | Board label, load group, phase allocation and current source. | Load schedule and maximum-demand checks. |
Next checks
- If the question is current only, keep power, voltage, phase and PF source together.
- If the current feeds voltage drop, carry the current source into the cable route and conductor data.
- If the current feeds demand or phase balancing, keep board label and phase allocation visible.
- If the current will affect wiring, protection, connection or testing work, keep licensed project review in control.
Boundaries
- A load-current value does not size a cable or protective device by itself.
- It does not replace measured values, product data, project schedules or current standards context.
- It does not decide demand, diversity or current-carrying capacity.
- Final installation and verification decisions belong to qualified project processes.