MCB inrush compatibility method
The checker compares peak inrush current with the selected MCB magnetic-trip band and separately checks whether available fault current reaches the conservative upper magnetic threshold.
Kinrush = Iinrush / InImag = 3-5 × InImag = 5-10 × InImag = 10-20 × Inwhere:
- Kinrush
- Inrush current as a multiple of breaker rated current
- Iinrush
- Peak equipment energization current[A]
- In
- MCB rated current[A]
- Imag
- Generic instantaneous magnetic operating band[A]
Below the lower threshold magnetic tripping is not expected, inside the band operation is uncertain, and above the upper threshold magnetic tripping is expected. Exact time still requires the manufacturer curve.
How to check MCB inrush compatibility
Select the breaker rated current and curve, then enter peak inrush current, pulse duration, available fault current, and breaking capacity. The checker compares the pulse with the generic magnetic band while keeping fault clearance as a separate requirement.
- Confirm MCB rated current from load and cable sizing.
- Obtain peak inrush and duration.
- Compare with the B, C, or D magnetic band.
- Verify available fault current and breaking capacity.
- Read the exact manufacturer time-current curve.
B16, C16, and D16 example
A 90 A inrush equals 5.625 × In for a 16 A breaker. It is above the B-curve upper threshold, inside the C-curve tolerance band, and below the D-curve lower threshold. That comparison describes magnetic-trip likelihood, not final circuit suitability.
Kinrush = 90 / 16 = 5.625
B16: 48-80 A; C16: 80-160 A; D16: 160-320 A
Ride-through versus fault clearance
A slower magnetic curve can reduce nuisance trips but requires more fault current for instantaneous operation. Long cables and high loop impedance can make a C or D curve fail the required disconnection condition even when it rides through startup.
Why exact trip time is not shown
Pulse shape, duration, prior thermal loading, ambient temperature, product tolerance, standard, and manufacturer design all affect operation. Use this tool to identify safe, uncertain, and likely-trip regions, then verify the exact device curve.
Assumptions
- IEC-style B, C, and D magnetic bands
- Peak inrush and available fault current are known or reasonably estimated
- Thermal-memory and manufacturer-specific curve tolerances are not modeled
Important Warnings
- The checker cannot predict exact trip time across brands; use the selected manufacturer's time-current curve and equipment inrush waveform.
- A curve that rides through inrush may still fail required fault-disconnection time if loop impedance is too high.