How to Calculate Motor Starter
What is Motor Starter?
Motor Starter Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
Starter Size = Motor HP × FLA × Service Factor
Step-by-Step Guide
- 1Look up motor FLA from nameplate, select starter amperage class
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
10 HP motor, 28A FLA, 1.15 SF
Result
Starter must handle 28 × 1.15 = 32.2A → use Size 1
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
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