1 in through air and 2 in over surface between uninsulated live parts of opposite polarity meets requirements for feeder and branch circuit applications of UL508A|Polycarbonate safety covers provide dead-front protection|All sizes have optional adder poles for increased flexibility and ease-of-use|Adder poles can be stacked to form multi-pole units in the field without the use of tools, adder poles allow for customization of primary and secondary wire combinations|End barriers are also available for sale, catalog numbers can be found in the catalog number selection tables for each size block|Aluminum connectors accept both aluminum or copper wire while copper connectors accept copper wire only and all 1-piece tin plated|Insulators are virtually unbreakable, made of glass filled polycarbonate, see-through hinged safety covers are optional and provide a greater degree of safety and shock resistance where required, hinged covers can be installed without tools|Each cover has a test probe hole in the center for circuit checking|Covers are optional accessories and catalog numbers can be found in the catalog selection tables for each size block|One cover is needed for each pole