The HAT903CSDC12 is a heavy-duty SPDT electromechanical relay from the HAT-900 series designed for high-current switching applications. It features 40A normally open and 20A normally closed contact ratings with silver cadmium oxide contacts on a copper base, providing reliable performance in demanding industrial environments. The relay operates with a 12 VDC coil and exhibits a pull-in voltage of 75% of nominal (9 VDC) and drop-out voltage of 10% of nominal (1.2 VDC minimum) at 25°C, with a maximum contact resistance of 20 mO. It is rated for Class B operating temperatures from -40°C to 85°C and provides 10 MO minimum insulation resistance at 500 VDC with 2000 VAC dielectric strength between contact and coil, frame and contact, and coil and frame. The relay is sealed for wave soldering and washing, making it suitable for automated assembly lines in power distribution, motor control, and switching applications.