Circuit Breaker Selection
Select a miniature circuit breaker from load current, ambient temperature, and trip curve; check cable ampacity and motor-start inrush.
Key points
Circuit Breaker Selection: Select a miniature circuit breaker from load current, ambient temperature, and trip curve; check cable ampacity and motor-start inrush. Formula: I_n ≥ K·I_load/temperature factor | I_n ≤ I_z (cable ampacity) | magnetic trip > inrush. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. Breaker In must be both ≥ design load current (with margin) and ≤ cable ampacity Iz; both conditions are mandatory. B / C / D curves set the magnetic-trip threshold. Motor inrush can reach 6–8×In; if C still trips, use D or a larger frame.
Inputs
I_n ≥ K·I_load/temperature factor | I_n ≤ I_z (cable ampacity) | magnetic trip > inrushCalculation model (updates with parameters)
| Design load current I_load | 32 A | 已含load率 / 同时系数 |
| Ambient-temperature derating factor | 95 % | 30°C 为 100%, by近似曲线 |
| Required minimum current rating | 42.11 A | K·I_load/Temperature系数 = 1.25×32 A/0.95 |
| Recommended breaker In | 50 A | 按常用壳架额定current向上取整 |
| Actual current margin | 1.56 × | recommend ≥1.1~1.25× |
| Trip curve / magnetic range | C 曲线（5~10×In） | B 阻性、C General、D motor / 变压器 |
| Cable ampacity check | 通过 ✓ | In 50 A ≤ I_z 63 A |
| Motor starting check | 不适用 | 阻性Load无启动冲击 |
Engineering notes
- Breaker In must be both ≥ design load current (with margin) and ≤ cable ampacity Iz; both conditions are mandatory.
- B / C / D curves set the magnetic-trip threshold. Motor inrush can reach 6–8×In; if C still trips, use D or a larger frame.
- Ambient temperature, side-by-side mounting, harmonics, and altitude reduce actual ampacity; critical circuits also need breaking-capacity and selectivity checks.
FAQ
- What is Circuit Breaker Selection for?
- Select a miniature circuit breaker from load current, ambient temperature, and trip curve; check cable ampacity and motor-start inrush.
- What is the formula for Circuit Breaker Selection?
- Core formula: I_n ≥ K·I_load/temperature factor | I_n ≤ I_z (cable ampacity) | magnetic trip > inrush. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Circuit Breaker Selection?
- Breaker In must be both ≥ design load current (with margin) and ≤ cable ampacity Iz; both conditions are mandatory. B / C / D curves set the magnetic-trip threshold. Motor inrush can reach 6–8×In; if C still trips, use D or a larger frame. Ambient temperature, side-by-side mounting, harmonics, and altitude reduce actual ampacity; critical circuits also need breaking-capacity and selectivity checks.