The Siemens 5SV8700-0KK is a SENTRON summation current transformer designed for AC systems. It's the sensing element for residual current monitoring — you pair it with an RCCB or RCBO to detect leakage currents down to 30 mA minimum (Idn). The 20 mm internal diameter passes the phase and neutral conductors through; the transformer sums their magnetic fields and reports any imbalance as a residual current signal.
Screw-type terminals accept 0.13 mm² to 2.1 mm² conductors — solid or ferruled stranded. The housing is IP20 at the connection terminals, so it's intended for enclosed panel mounting, not washdown zones. Dimensions are compact: 46 mm wide, 60 mm deep, 32 mm tall, which fits a standard DIN-rail footprint alongside a 2-pole or 4-pole RCCB. Maximum wire length from the transformer to the evaluation unit is 10 m — keep that in mind when routing in a large panel. The transformer itself has no error memory (no latching fault indication), so the connected RCD handles the trip and reset logic.