The ABB F204 B-125/0,5 is a 4-pole residual current circuit breaker (RCCB) rated for 125 A continuous current and 500 mA residual trip threshold. It is a Type B device, meaning it detects smooth DC fault currents as well as AC and pulsed DC — essential for drives, UPS systems, and PV inverters where pure sine-wave residual currents can blind a standard AC or A-type RCCB. Rated 230/400 V AC, it fits three-phase four-wire networks (TN-S, TT) common in European industrial panels.
The 125 A rated current (In) is the continuous load the RCCB can carry without overheating. For a 125 A frame, expect the upstream breaker to be sized at or below this — coordination studies typically target 80 % loading for thermal headroom in a 40 °C ambient. The 500 mA residual current is a high-threshold device — not for personnel protection (which needs 30 mA or less), but for equipment protection or fire prevention on large feeders where nuisance tripping from cable capacitance would plague a lower-sensitivity unit. Type B detection covers frequencies up to 1 kHz or more, so it handles the mixed-frequency leakage from VFD output cables without false trips. Pollution degree 2 means the RCCB is rated for non-conductive pollution that might become temporarily conductive due to condensation — typical of a clean industrial panel, not a washdown zone. The IP2X housing protects against fingers (12 mm probe), not water ingress. Power loss per pole is 7.5 W at rated conditions, so the total dissipation across four poles is 30 W. That heat must be considered in a crowded DIN-rail enclosure — adjacent devices may need derating or spacing.