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Selects appropriate circuit breaker to protect circuits from overcurrent while allowing normal operation. Wrong sizing causes nuisance trips or fire risk.
Формула
Typical breaker = current × 1.25 (non-motor) or × 2.5 (motor)
Водич корак по корак
- 1Calculate circuit maximum current
- 2Breaker must exceed running current for motor inrush
- 3Typical breaker = current × 1.25 (non-motor) or × 2.5 (motor)
- 4Match breaker to wire ampacity (wire must handle breaker rating)
- 5Select trip curve (A, B, C, D) for application
Worked Examples
Инпут
40A circuit, #8 wire
Резултат
50A breaker
Common Mistakes to Avoid
- ✕Oversizing breaker to avoid nuisance trips (creates fire hazard)
- ✕Using undersized wire for breaker rating
Frequently Asked Questions
Why not just use larger breaker?
Oversized breaker won't protect from short circuits, creating fire/electrocution risk.
What's the difference between breaker curves?
A: sensitive (electronics), B: general, C: motors, D: high inrush; choose for application.
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