What it is and what it does
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. It occupies 3 modular width units (54 mm) on a DIN rail and carries an IP20 finger-safe enclosure for panel-mount duty.
Key ratings and what they mean for fit
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. This is not optional — the 4 W power loss per pole at rated current adds up, and stacking contactors without airflow gaps will shorten coil life. Plan for the extra width when laying out the panel.
Where it fits in the panel
As a DIN-rail mounted insta contactor, it's used in distribution boards and control panels for switching lighting, heating, and motor loads where the NC contact configuration is needed. The 4 NC contacts can handle up to 4,000 W incandescent lamp load across the set.