The Siemens 5SV8704-0KK is a SENTRON summation current transformer, Type A, designed for AC systems. It carries a rated operational current of 250 A and a minimum residual current detection down to 100 mA, with a 105 mm internal diameter that accommodates multiple conductors or busbars through the window.
The 105 mm internal diameter is the key mechanical fit dimension — it determines the maximum bundle or busbar cross-section that can pass through the transformer. Rated for 250 A continuous, it suits main feeders or large sub-distribution circuits. The 100 mA minimum residual current means it can detect earth faults down to that threshold, which is typical for Type A devices that catch AC and pulsed DC fault currents. Screw-type terminals accept conductors from 0.13 mm² to 2.1 mm², so the secondary wiring is straightforward for standard control cables.
This transformer mounts in the enclosure around the main conductors or cable bundle — it is not a DIN-rail component. The IP20 rating at the connection terminals means it is suitable for dry, clean indoor panels where no water ingress is expected. The 146 mm depth and 170 mm width give a compact footprint for a 105 mm ID window; plan for at least that clearance around the mounting surface.