Motor protection relay for screw-terminal panels
The Siemens 3RU1146-4KB1 is a SIRIUS thermal overload relay — the part that sits between the contactor and the motor to protect against sustained overcurrent. Rated for screw-type terminals on both the main circuit and the auxiliary/control circuit — no crimp lugs or ring terminals needed for the power wiring. The S3 frame size accepts stranded conductors up to 70 mm² on the main poles.
Trip class, coordination, and ATEX
Short-circuit coordination is specified for both Type 1 and Type 2: with a gG fuse rated 250 A (Type 1) or 160 A (Type 2), the relay withstands fault currents without damage to the downstream contactor. Surge voltage resistance is 8 kV. Carries ATEX approval (DMT 98 ATEX G 001) for use in potentially explosive gas atmospheres — the relay can be part of a motor protection scheme in Zone 1 or Zone 2 areas when paired with an appropriate contactor and upstream protection.
Panel fit and environmental tolerance
Dimensions are 70 mm wide, 120 mm high, and 140 mm deep — the S3 footprint matches the SIRIUS 3RT2 contactor range for direct mounting. Stand-alone installation is standard, with the mounting surface vertical and rotatable ±135° or tiltable ±45° front/back. Rated for 100 % relative humidity during operation. Shock resistance is 8 g for 10 ms — suitable for machine-mounted panels on presses, conveyors, or compressors where vibration is present.
Wiring and auxiliary contact ratings
Auxiliary terminals accept AWG 20…16 and 18…14 (two wires per terminal). Power dissipation is 6.3 W per pole — account for this heat in the panel thermal budget, especially when multiple relays are ganged side-by-side. Minimum side clearance is 6 mm.