Step 1: Choose a correct control Mode AA - AC Control AC DA - DC Control AC Step 2: Choose a correct type Current of Equipment/Ratio = Current of SSR PS: The Ratio depend on the kind of your loading equipment. Resistive load :70%, Inductive load:20%,Capacitive load10%. Step 3: Choose a suitable heat sink During the useage of SSR, it will give out a lot of heat, so in order to extend the life of your SSR, please install a heat sink , also if the current is over 60A,the cooling fan also required. PS: Our Heat Sink include 2 screws (for install heat sink) and a pack of thermal compound (is applied to the bottom of the SSR) Notice: The inside of the solid-state relay is a semiconductor. A semiconductor switch is a non-physical contact switch. if use a multimeter diode or resistor to test ,it always show a high-impedance state, (multimeter light red). According to the conventional detection methods of solid state relays: a load is required to test the switching state. Using an incandescent lamp as a dummy load is an obvious way to test continuity.