The Schneider Electric LR3D1521 is a non-differential thermal overload relay from the TeSys LRD series, designed for motor protection in control panels. It provides adjustable thermal protection from 12 to 18 A with a Class 20 tripping curve, meaning it allows a 20-second hot-start locked-rotor withstand — standard for general-purpose induction motors driving pumps, fans, and conveyors. The relay offers phase-failure sensitivity: it trips at 130 % of the set current (Ir) on two phases when the third drops to zero, preventing single-phasing damage. Auxiliary contacts are 1 NO + 1 NC, rated 1.5 A at 240 V AC-15 for signalling circuits and 0.1 A at 250 V DC-13.
If a direct replacement is needed, a parametric search within the TeSys LRD family for a 12-18 A thermal overload relay with Class 20 and 1 NO + 1 NC contacts is the practical next step, but pin-to-pin compatibility must be verified against the panel wiring and contactor interface.
Dimensions are 45 mm wide by 92 mm deep, fitting a standard 45 mm modular envelope. Screw-clamp terminals accept power circuit conductors up to 10 mm² flexible without cable end, and control circuit conductors up to 2.5 mm². IP20 finger-safe protection is provided per IEC 60529, suitable for enclosed panel installation.
The LR3D1521 carries multiple international standards: EN/IEC 60947-4-1 and -5-1 for contactors and control-circuit devices, UL 60947-4-1 and -5-1, CSA C22.2 No 60947-4-1 and -5-1, plus GB/T 14048.4 and.5 for the Chinese market. Rated insulation voltage (Ui) is 600 V for UL/CSA and 690 V for IEC. Impulse withstand voltage (Uimp) is 6 kV. Flame retardance is V1 per UL 94. Dielectric strength tested at 1.89 kV at 50 Hz per IEC 60947-1. The relay withstands 6 Gn vibration and 15 Gn shock per IEC 60068-2-6 and -2-7.