The Siemens SENTRON 5TT5043-2 is an insta contactor with 4 normally-closed (NC) contacts, rated for 40 A operational current at 400 V AC, with a 24 V DC control coil. This is a compact, panel-mount switching device — 3 modular width units wide (53.5 mm) — designed for DIN-rail installation in distribution boards and control cabinets. The 4 NC contacts stay closed when the coil is de-energized, so this contactor suits fail-safe or normally-on circuits where the load must remain connected unless the coil is actively held open.
The 40 A AC rating at 400 V defines the maximum resistive or lightly inductive load this contactor can switch. For motor loads or other inductive circuits, derate per the AC-3 duty curve — 40 A is the AC-1 (resistive) figure. A critical installation detail: the manufacturer requires spacers between adjacent devices to ensure adequate heat dissipation. This is not optional — stacking these contactors without the specified air gap will shorten coil life and may cause nuisance tripping under sustained load. Factor the spacer width into your DIN-rail layout before committing the panel design.
Its 3-module footprint (53.5 mm wide, 90 mm tall, 71 mm deep with 64 mm installation depth) fits standard SENTRON and SIRIUS enclosure cutouts. Typical deployment: switching resistive loads such as lighting banks, heating elements, or transformer primaries where the normally-closed contact arrangement is needed for a safety or standby circuit.