The Eaton TF42-38 is a thermal bi-metallic overload relay in the A-Line family, rated for 35.0 to 40.0 Amp motor circuits. Selectable manual or automatic reset gives the commissioning engineer a choice: auto for remote or unmanned sites, manual for attended lines where you want a positive reset after a fault.
The 35-40 A range is the adjustable full-load current window, set via the dial on the relay face. For a controls integrator wiring a 15 kW (20 HP) motor at 400 V — which draws roughly 28-30 A full-load — you'd dial it to the motor nameplate FLA. The Trip Class 10 curve means it clears a fault before the motor insulation sees damaging heat, but won't drop out on a normal start that clears in under 10 seconds. Spring-cage terminals on the relay accept 0.2-2.5 mm² stranded or solid copper — standard for panel wiring. The reset mode selector (manual/auto) is a slide switch on the front; if you're wiring a safety circuit that requires manual reset after a trip, set it before power-up.