Contact Blocks for Operators in Cover 1 NOâ„spring returnâ„1 speed. Range of product Harmony XAC Product or component type Contact block Component name ZB2 Electrical circuit type Control circuit Contact block application Single speed Contact block type Single Type of operator Spring return Product compatibility XACA XAPS2 XB4 XB5 Contacts type and composition 1 NO Mounting of block Front mounting Contacts operation Slow-break Complementary Connections - terminals Screw clamps terminals (2 x 1.5 mm²)with or without.