The Siemens 5TT5042-2 is a SENTRON Insta contactor with 2 normally-open and 2 normally-closed contacts, rated for 400 V AC and a 40 A switching capacity. The coil is 24 V AC/DC, so it works with either supply — no separate coil voltage variant needed for mixed-control panels. At 3 modular width units (roughly 53.5 mm wide), it snaps onto a DIN rail inside an enclosure. The 71 mm depth (64 mm installation depth) fits standard 80 mm deep enclosures, but the manufacturer notes that spacers are required between units for heat dissipation — don't pack them tight without air gaps.
Contact configuration and coil drive
The 2 NO + 2 NC contact arrangement gives you one set for the load and one for a feedback signal or interlock, without adding an auxiliary contact block. The 24 V AC/DC coil draws 4 W per pole in hot operating state at rated current — factor that into your power supply budget if you're running several contactors in a row. The coil accepts both AC and DC, so a single 24 V power supply can drive the whole panel. No need to run a separate AC control transformer just for this contactor.