The 3RB1253-0FM00: This relay supports continuous or individual mounting, with busbar connection on the main circuit and screw terminals on the auxiliary circuit. It includes manual, automatic, and remote reset options, monostable outputs, and ground fault signaling — a feature that detects leakage current to earth and trips the contactor, which is useful on ungrounded or IT systems where a single ground fault won't blow a fuse but still needs to be caught. The control supply is AC 220-240 V, 50/60 Hz. That voltage powers the internal electronics for ground fault detection and the reset coil; the main power path through the relay is passive — it's the bimetallic or electronic sensing element that tracks motor current, not the control voltage.
There is no official Siemens successor order code listed for this relay; if you need an active-production alternative, a parametric search for a Size S6 overload relay with the same current range and ground fault signaling is the practical route.
Trip class adjustment from 5 to 30 means you can set the relay to ignore inrush current for up to 30 seconds at 7.2× FLC (the standard test point). Class 5 is for short acceleration times like fans; Class 30 is for high-inertia loads. The ground fault signaling output is a separate auxiliary contact that changes state when leakage exceeds the internal threshold — useful for feeding a PLC input or annunciator panel.