The Siemens SENTRON 5TT5840-8 is an Insta contactor with 4 normally open contacts, designed for switching loads on 400 V AC circuits up to 40 A, with a 24 V AC control coil.
The 24 V AC coil is standard for control transformers or PLC relay outputs; verify your control voltage is AC, not DC, because the coil is AC-rated only. Switching capacity for incandescent lamp loads is listed at 4 000 W, which is the figure to use when sizing for lighting circuits — the 40 A general rating is for resistive or motor loads, and lamp inrush current requires this derated power limit. The 4 NO contact configuration (zero NC) means this contactor is a make-only device — it closes all four poles when the coil is energized. If your circuit needs a normally closed auxiliary for status feedback or interlocking, you will need an add-on auxiliary contact block; the product extension slot supports supplementary devices.
Installation and panel integration
IP20 protection class means it is suitable for dry indoor panels only — no washdown, no outdoor exposure without an additional enclosure. Power loss is 4 W per pole in hot operating state at rated AC current. In a multi-contactor panel, sum these losses to check your enclosure thermal budget; four contactors at full load add 64 W of heat.