Generator starting kVA in Australian backup-power planning
How generator starting kVA uses running load, selected motor, starting method, multiplier and voltage basis.
What Generator Starting kVA Means
Generator starting kVA is a planning value used when a generator must support motor starting or another high-starting-current event. It sits beside other running load, the selected motor, motor full-load current, starting multiplier and voltage-dip context.
The value screens a starting event. It does not select a generator, prove transient performance, approve a changeover arrangement or settle earthing, MEN, neutral switching, RCD or protection questions.
Formula Fields
The motor starting current estimate is:
I_start = I_fl x m.
For a three-phase motor, S_motor_start = sqrt(3) x V x I_start / 1000. For a single-phase motor, use S_motor_start = V x I_start / 1000.
The starting-event kVA is S_event = other running load + S_motor_start.
For Australian worksheets, 230 V single-phase and 400 V three-phase are common nominal bases when they match the project. The starting multiplier should come from manufacturer data, starter type or a clearly entered assumption.
| Input | Use it for | Why it matters |
|---|---|---|
| Other running load | Loads already connected before the start. | Starting event includes the running load that remains on. |
| Selected motor | The motor or load being started. | The largest or first-starting motor often drives the review. |
| Starting multiplier | DOL, star-delta, soft starter, VSD or manufacturer-entered value. | The multiplier changes starting current directly. |
| Voltage and phase | 230 V single-phase or 400 V three-phase where applicable. | Apparent power calculation changes with phase. |
| Generator comparison kVA | Optional entered comparison value. | It is a screening comparison, not product selection. |
Worked Starting Event
A 400 V three-phase pump has I_fl = 32 A and a DOL starting multiplier of 6. The starting current is:
I_start = 32 x 6 = 192 A.
S_motor_start = sqrt(3) x 400 x 192 / 1000 = 133.0 kVA.
If other running load is 35 kVA, then S_event = 35 + 133.0 = 168.0 kVA. A generator comparison value must come from supplier, manufacturer or project review before it is used.
| Field | Example entry | Reading |
|---|---|---|
| Other running load | 35 kVA already connected. | The motor does not start into an empty load list. |
| Selected motor | 32 A three-phase pump. | The worksheet focuses on one named starting event. |
| Starting method | DOL with multiplier 6. | Replace with manufacturer data where available. |
| Starting-event kVA | 168.0 kVA. | Compare only with entered generator or supplier data. |
Load Sequence And Product Review
The load sequence matters. Some loads may already be running, some may be delayed or shed, and some motors may start one at a time. Do not add every possible motor start unless the project sequence says they start together.
DOL, star-delta, soft starter, VSD and other starting methods can all change the multiplier. Alternator transient capability, engine response, fuel system, voltage dip, controls and manufacturer limits can change the final generator review even when the worksheet value looks acceptable.
Next checks
- Use generator load and starting kVA when running loads, selected motor, starting method and comparison basis are ready.
- Use motor starting current when the selected motor starting value needs its own estimate first.
- Use motor nameplate fields to keep FLC, starting method and product data traceable.
Boundaries
- This page does not select a generator or approve a backup-power installation.
- It does not model all voltage dip, alternator, engine, fuel, changeover, earthing, MEN, neutral switching, RCD or protection behaviour.
- Manufacturer data, supplier advice, AS/NZS 3010 context, AS/NZS 3000 context, DNSP or local authority requirements, project requirements and engineering review remain controlling inputs.