What the ratings mean for fit
The SENTRON 5SM9642-0KK is a 4-pole residual current unit rated 40 A at 400 V AC, with a 300 mA trip threshold and Type AC waveform detection. The 300 mA sensitivity is for equipment protection or fire prevention, not personnel protection. The instantaneous design trips as soon as residual current exceeds 300 mA. The 50 Hz supply frequency is fixed.
Panel integration note
Snap-on DIN rail mounting, standard for SENTRON modular devices. The 4-pole width occupies the same footprint as a 4-pole MCB, fitting existing distribution boards.