What this control unit does
The Schneider LUCA12BTQ is a standard control unit in the TeSys U motor starter range, designed for basic motor protection: overload, short-circuit, phase failure, and earth fault. It operates on a 24 V AC control circuit and is rated for motor power up to 5.5 kW at 400...440 V AC, 5.5 kW at 500 V AC, and 9 kW at 690 V AC.
Mounts via plug-in front face onto a TeSys U power base or contactor — no DIN-rail tool needed, just snap it in. Dimensions are 66 mm high, 45 mm wide, 60 mm deep, fitting the standard TeSys U footprint. IP20 on the front panel and wired terminals; IP40 on the front panel outside the connection zone. Control circuit voltage limits are 20...26.5 V AC for operation, with dropout at 14.5 V AC — so a saggy 24 V supply that dips below 20 V will drop the starter out, which matters if you're sharing a control transformer with other loads.
Protection and coordination
Tripping threshold is 14.2 x Ir ±20 %, giving a short-circuit trip fast enough to coordinate with most upstream MCCBs or fuses. Phase failure sensitivity is built in — no separate module needed. Immunity to microbreaks is 3 ms, so brief line sags won't cause nuisance dropouts. Safe separation of 400 V SELV between control/auxiliary and main circuits means you can share a 24 V control bus without worrying about creepage to line voltage.