The Siemens 5TT5851-2 is a SENTRON Insta contactor with a 24 V AC coil and a 3 NO + 1 NC contact arrangement, rated for 400V 63A main pole switching.
Panel fit and heat management
The 54 mm width (3 MW units) matches the common breaker footprint, so it rows cleanly alongside SENTRON MCBs. The 71 mm depth leaves clearance behind the mounting plate — no overhang issue. The critical detail: the spec explicitly requires spacers between adjacent units for heat dissipation. At 8 W per pole in hot state, stacking contactors without gaps will derate the assembly. Plan for a 1-module spacer or leave an empty slot between each 5TT5851-2 if you're grouping several. IP20 rated — fine for enclosed panels, not for washdown zones or outdoor cabinets without a secondary enclosure.
What the contact arrangement means on the line
The single normally-closed contact gives you a feedback or interlock path without adding an auxiliary block. The 5 000 W incandescent lamp rating confirms it handles the high inrush of cold filaments, so it's a fit for lighting contactor duty where incandescent or halogen loads are present.