Choose thermal-magnetic when the load is simple and the protection curve does not need adjustment — distribution circuits, standard motor circuits, and applications where the breaker is set once and left alone. Choose electronic trip when you need an adjustable setting current range (our GNM1E covers 0.4–1.0In), configurable long-time / short-time / instantaneous protection, or communication capability for remote monitoring. Electronic trip units also handle wide current ranges better, reducing the number of SKUs a panel builder needs to stock.

Because the rated current is defined at a reference ambient temperature — typically 40°C. Above that, the bimetal strip inside the thermal element sits closer to its trip threshold even at normal current, so it takes less overload to trip it, and it may nuisance-trip on a healthy circuit. At 50°C the factor is 0.91, at 60°C it drops to 0.82. If your calculated load is 220A and you select a 250A frame, at 50°C the effective capacity is only 228A — a narrow margin that leaves no room for transient peaks or future load growth.

Icu (ultimate short-circuit breaking capacity) is the maximum fault current the breaker can interrupt without failing catastrophically — but after a fault at this level, the breaker may not be reusable. Ics (service short-circuit breaking capacity) is the fault current the breaker can interrupt and then continue to operate normally. Ics is always lower than Icu, and the ratio between them tells you how robust the breaker is. A high Ics/Icu ratio (for example, 65kA Ics against 85kA Icu on the GNM1-250H) means the breaker can clear a severe fault and still be put back into service.

Choose the motor protection type when the MCCB feeds a motor directly, without a separate overload relay. The motor protection trip unit has a magnetic trip threshold set higher — typically 12–14In instead of the standard 10In — so it does not trip on the motor's normal starting inrush, which can reach 6–8 times rated current for several seconds. The distribution type would see that inrush as a short circuit and trip. If you already have a separate thermal overload relay in the motor circuit, the standard distribution type is sufficient.

At high altitude, the air is thinner, which affects the breaker in two ways. First, cooling is less effective — the bimetal strip and current-carrying parts run hotter for the same current, so the working current must be reduced. Second, insulation withstand is lower — the reduced air density makes it easier for an arc to form across the contact gap, so the breaking capacity must also be corrected. IEC 60947-2 provides correction factors for altitudes above 2000m. Both corrections are required, not just one.

Yes. MOQ is 1 unit, and standard lead time is 7–15 working days. This allows buyers to verify the trip characteristics, mounting dimensions, and terminal arrangement on a real unit before placing a production order. Custom configurations — special trip curves, non-standard terminal types, or specific nameplate requirements — are also available on request, with lead time confirmed at the time of order.