The Siemens 5TT5843-2 is a SENTRON insta contactor with 4 normally-closed (NC) contacts, controlled by a 24 V AC coil and rated for 400 V at 40 A.
The 4 NC contacts are all normally-closed — zero NO contacts — so this contactor is designed for fail-safe circuits where the load must be disconnected when the coil is de-energized. Think safety interlocks, emergency-stop chains, or holding circuits that drop out on power loss. The 400 V / 40 A rating on the description covers resistive and motor switching at that voltage level. The 24 V AC coil means it pulls from a control transformer, not a DC supply — verify your control voltage type before wiring. IP20 protection means it's safe from finger contact but not water ingress — strictly indoor panel use. The 71 mm depth and 90 mm height fit standard DIN-rail enclosures; the 54 mm width (3 MW) occupies three adjacent 18 mm module slots.
Installation note — spacing matters
Siemens explicitly requires spacers between adjacent units for heat dissipation. Plan for the extra width when laying out the panel.
The 4 NC contacts can handle up to 4,000 W incandescent lamp load across the set.