The S2840B Series of normally closed, ac solid-state relays is designed for controlling medium-sized loads. The relays feature back-to-back SCR outputs capable of switching 40 A at line voltages to 280 vac, and withstanding transient voltages to 600 Vpk, says the company. The units are offered in 25 and 40 A models with input control of 5, 12, or 24 vdc. In form B configuration, the output remains closed with an open circuit or a low signal on the control. In addition, 2,500 V optical isolation protects input control elements from load signal transients, says the company.