Motor Protection Circuit Breaker (MPCB) Selection
Select MPCB frame, thermal-magnetic trip range, and breaking capacity from motor rated current, starting current, and prospective short-circuit current.
Key points
Motor Protection Circuit Breaker (MPCB) Selection: Select MPCB frame, thermal-magnetic trip range, and breaking capacity from motor rated current, starting current, and prospective short-circuit current. Formula: I_set ≈ I_e | magnetic trip ≈ 12×I_n | I_cu ≥ I_sc. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. An MPCB combines thermal overload and magnetic short-circuit protection; set the thermal trip to motor FLA and keep the magnetic trip above starting current. Breaking capacity must exceed the prospective short-circuit current at the installation point; if not, add backup fuses or use a higher I_cu model.
Inputs
I_set ≈ I_e | magnetic trip ≈ 12×I_n | I_cu ≥ I_scCalculation model (updates with parameters)
| Recommended MPCB frame | 32 A | 所needs ≥ 26.32 A（含Temperature降额） |
| Thermal trip setting I_set | 25 A | 按motor FLA 整定，留 ±10% 调knot |
| Magnetic trip current (approx.) | 384 A | 常见 12×I_n，实际以厂家曲线为准 |
| Motor starting current | 150 A | I_e×6.0 |
| Starting nuisance-trip check | 通过 ✓ | 磁脱扣 ≥ 启动current |
| Breaking capacity check | 通过 ✓ | I_cu 25.0 kA ≥ I_sc 10.0 kA |
| Ambient derating | 95 % | 30°C 为基准 |
| Protection coordination | MPCB + 接触器 + 热继 | MPCB 可替代Thermal relay + 微断组合，但仍需按启动and短路配合选型 |
Engineering notes
- An MPCB combines thermal overload and magnetic short-circuit protection; set the thermal trip to motor FLA and keep the magnetic trip above starting current.
- Breaking capacity must exceed the prospective short-circuit current at the installation point; if not, add backup fuses or use a higher I_cu model.
- For frequent starts, heavy starts, or high ambient temperature, follow manufacturer derating and coordinate with contactor / thermal-relay characteristics.
FAQ
- What is Motor Protection Circuit Breaker (MPCB) Selection for?
- Select MPCB frame, thermal-magnetic trip range, and breaking capacity from motor rated current, starting current, and prospective short-circuit current.
- What is the formula for Motor Protection Circuit Breaker (MPCB) Selection?
- Core formula: I_set ≈ I_e | magnetic trip ≈ 12×I_n | I_cu ≥ I_sc. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Motor Protection Circuit Breaker (MPCB) Selection?
- An MPCB combines thermal overload and magnetic short-circuit protection; set the thermal trip to motor FLA and keep the magnetic trip above starting current. Breaking capacity must exceed the prospective short-circuit current at the installation point; if not, add backup fuses or use a higher I_cu model. For frequent starts, heavy starts, or high ambient temperature, follow manufacturer derating and coordinate with contactor / thermal-relay characteristics.