What it is and what it does
The Siemens 5TT5701-0 is an Insta contactor carrying one normally-open and one normally-closed contact, rated for 20 A at 230/400 V AC with a 230 V AC coil. The 1NO+1NC contact arrangement gives you both a make and break contact in a single device — useful for interlocking or signalling alongside the main load switching.
Where it fits
As a DIN-rail-mounted contactor in the Insta series, the 5TT5701-0 snaps onto standard 35 mm rail inside a distribution board or control panel. The 20 A rating at 400 V AC suits it for switching resistive or moderate inductive loads — lighting banks, small heaters, or as a slave contactor in larger motor starter assemblies.