Motors & Loads calculator
Motor Starter Calculator
Enter motor power, voltage, phase count, starter family, actual nameplate FLA, control-voltage data, enclosure context, and ambient assumptions to run a preliminary motor-starter screen for U.S. motor-control work. The page combines a common NEMA starter-size check for standard three-phase horsepower ranges, a controller current-class screen when a direct NEMA horsepower table is not the right basis, an overload-relay review from actual motor nameplate FLA, and simple control-package notes. It is intentionally narrower than a full MCC, SCCR, or drive-package study.
Updated July 10, 2026
Enter motor HP or kW, voltage, phase count, starter family, and actual nameplate FLA to screen starter size, controller current class, and overload-relay basis.
Method path: motor data -> starter family -> NEMA or controller-current screen -> nameplate FLA overload review -> catalog and SCCR checks.
Enter motor HP or kW, voltage, phase count, and starter family below to screen NEMA size, controller current class, and overload-relay basis
Example Calculations
More examples. Open to review 1 additional calculation example.
How to Use
How to use the motor starter calculator
- Select the calculation mode: starter sizing, overload review, control review, or the combined complete screen.
- Enter the motor power, voltage, phase count, and starter type.
- For a magnetic or combination starter, the calculator will screen the smallest common NEMA size that covers the selected motor in the chosen voltage group.
- For manual starters, soft starters, and VFDs, the calculator shifts to an honest controller-current review instead of pretending one universal NEMA horsepower table solves every package.
- If you want overload-relay guidance, enter the actual motor nameplate FLA. This is important because overload settings follow the installed motor, not the NEC table full-load current used for branch-circuit sizing work.
What each mode covers
| Mode | Primary outputs | Best use |
|---|---|---|
| Starter sizing | NEMA starter size or controller current class, duty-cycle note, and current basis | Preliminary starter or contactor screening |
| Overload review | 115% and 125% nameplate-FLA review range plus overload basis note | Checking relay setting range from actual motor data |
| Control review | Control-voltage note, starting-method note, enclosure note, and ambient review | Early package and panel planning |
| Complete screen | All of the above in one result set | Coordinating a starter concept before detailed catalog selection |
Why this page separates table current and nameplate current
For U.S. NEC-oriented work, branch-circuit sizing tasks often begin with the standard full-load current values in the motor tables, while overload-relay settings follow the actual motor nameplate current. This calculator keeps that distinction visible instead of pretending one current value handles every job.
What the page does well
- It gives a practical NEMA starter-size screen for common three-phase starter work.
- It switches to a controller-current review for soft starters, VFDs, and manual starters where a single NEMA horsepower table would be misleading.
- It keeps overload-relay review tied to actual nameplate FLA.
- It shows the control-voltage and enclosure discussion without inventing fake coil-VA precision.
What this page does not claim to do
- It does not replace manufacturer catalog selection, SCCR review, short-circuit protection, or coordination studies.
- It does not model every severe-duty case, reversing package, or special motor family.
- It does not replace a drive package review for harmonics, bypass logic, or commissioning settings.
For a worked scenario, load one of the presets into the calculator above, replace the motor horsepower, voltage, starter family, and nameplate FLA with the installed motor data, then use the result panel for the starter screen and overload-relay review. Treat the preset as an input shortcut, not as a catalog selection.
Use the Motor Current Calculator when you need NEC table current or branch-circuit conductor screening, the Motor Starting Current Calculator for inrush comparisons, the Motor Cable Size Calculator for conductor review, and the Breaker Sizing Calculator for upstream device checks.
Common Applications
More applications. Open to review 2 additional use cases.
Frequently Asked Questions
How do you size a motor starter?
Start with motor horsepower, voltage, phase count, and starter family. For a common three-phase magnetic or combination starter, use the smallest published NEMA size that covers the motor at the selected voltage group. Then confirm the actual catalog horsepower rating, overload range, enclosure, and short-circuit rating.
Why does overload-relay review use nameplate FLA instead of the table current on this page?
Because overload devices protect the installed motor. The final relay setting follows the actual motor nameplate current and the selected relay instructions, while table-based full-load current is mainly part of the broader NEC motor-sizing workflow.
Is a motor starter the same thing as a breaker?
No. A starter is the control assembly that starts, stops, and protects the motor from overload through the contactor and relay package. The upstream breaker or fuse handles short-circuit and ground-fault protection and is a separate selection step.
How do soft starters and VFDs change the selection process?
They move the selection basis toward the controller current rating and the selected package details. You may still need a line or bypass contactor, but the final choice depends on the specific soft-starter or drive catalog rather than on one universal NEMA horsepower chart.
Can I use a NEMA starter size directly for single-phase motors?
Not as confidently as for the common three-phase starter tables. Single-phase applications often need a product-family and manufacturer check, so this page shifts toward an honest current-based review and a warning to verify the actual catalog.
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