What it is and where it fits
The Siemens 5TT5802-2 is a SENTRON Insta contactor — a compact, DIN-rail-mounted switching device with a 24 V AC coil and two normally-closed (NC) contacts rated for 20 A at 250 V AC. It occupies a single modular width (18 mm), so it slots into a standard distribution board or control panel without crowding adjacent breakers or relays. The 2 NC contacts mean the load circuit is closed when the coil is de-energised — useful for fail-safe shutdown, emergency-stop chains, or holding circuits where loss of control power must open the load. There are no normally-open contacts on this variant.
What the ratings mean for your panel
The 20 A AC operational current is the continuous carry rating under AC load. That covers most lighting, resistive heater, and small motor contactor duties within the 250 V AC line-to-line or line-to-neutral envelope. The 1000 W incandescent lamp switching capacity gives a quick check for lighting-circuit replacement: if the lamp bank pulls under 1 kW, this contactor handles the inrush without welding the contacts. Power loss runs 1.7 W per pole in hot operating state. That is low enough that a single unit in a closed panel won't need derating, but the installation note explicitly calls for spacers between adjacent devices to ensure heat dissipation — so don't pack them tight without the recommended air gap. IP20 means it's protected against solid objects larger than 12 mm (fingers) but not against moisture. It belongs inside a panel or enclosure with a higher-rated door — not on a washdown line or outdoors without a cover.