What it is and what it does
The Siemens 3RB1246-1QB20 is a solid state overload relay for full motor protection, covering the 6.3...25 A range with adjustable trip class from 5 to 30. It mounts individually in size S00 or S0 contactor footprints — common on smaller motor starters up to about 7.5 kW at 400 V. The auxiliary circuit runs on DC 24 V and provides monostable outputs for ground fault signaling. Reset is selectable between manual, automatic, or remote via the screw terminals. The integrated ground fault detection is the standout here — it catches leakage to earth before a hard fault develops, which saves chasing intermittent trips on wet or dusty lines.
Sourcing and lifecycle reality
For a BOM line that specifies the 3RB1246-1QB20, the supply posture is straightforward — quoted to order against an RFQ. No cross-reference or second-source is listed; the part is sourced as the original Siemens order code.
What the ratings mean for fit
The 6.3...25 A current range covers FLA for a typical 5.5 to 7.5 kW motor at 400 V three-phase. The adjustable trip class (5 to 30) lets you match the thermal curve to the motor's starting profile — Class 10 for standard starts, Class 20 for longer acceleration like conveyors, Class 30 for high-inertia loads such as fans or centrifuges. The DC 24 V auxiliary supply is common in modern control panels with PLC-based safety circuits. Ground fault detection with a monostable signaling output means the relay latches on a ground leak and sends a discrete signal back to the controller — no separate ground-fault module needed.