Motor Starting kVA Calculator — Estimate Starting Demand Before Connection
Estimate a motor's running current, starting current and starting kVA from the motor rating and the electrical assumptions you provide. This makes a high-demand starting event visible before a project is reviewed.
Motor and supply inputs
How motor starting kVA is estimated
The motor output is first converted to electrical input power using efficiency. Running current is then estimated from voltage, power factor and phase configuration. Starting current is the modeled running current multiplied by the starting-current multiple.
Why starting kVA matters
Starting demand is an apparent-power question because the supply must support voltage and current at the starting condition. A motor can therefore have a modest running kVA but a substantially higher starting requirement.
Why the multiplier is important
The same motor rating can produce very different starting currents depending on how it is started. Entering a multiplier rather than hard-coding one keeps the assumption visible.
Worked example
A 15 kW, 400 V, three-phase motor at 92% efficiency and 0.88 power factor has a modeled running current of roughly 28 A. At a 6× starting-current multiple, the estimated starting current is about 168 A.
What this tool does not decide
It does not select a generator, transformer, breaker, starter, cable or protection setting. Manufacturer data and the complete electrical system should be checked before equipment selection.
Practical use
This calculator is particularly useful during generator planning, transformer checks, temporary power planning and early motor installation coordination where starting events need to be discussed separately from normal operating demand.
Frequently asked questions
Is starting kVA the same as motor running kVA?
No. Starting demand can be substantially higher because starting current can exceed running current.
Can I use single-phase motors?
Yes. Select single-phase to use the corresponding current relationship.
Should I use the motor nameplate starting current?
When reliable manufacturer data is available, it should generally take precedence over a generic multiplier assumption.
Does this predict voltage dip?
No. Voltage dip also depends on source impedance or available short-circuit capacity. Use the separate voltage-dip estimator for that question.