Knockout arrangement providing connection pattern choice on electrical junction box and cover plate arrangement for mounting dynamic loads

An electrical junction box defined by a back wall having four planar side walls connected to and extending outwardly from said back wall and a knockout arrangement on at least one of said side walls for accepting two different diameter size conduits, said knockout arrangement comprising:

• (a) a pair of first knockout structures being spaced apart along said at least one side wall, each of said first knockout structures including a first circular knockout and a second annular knockout completely surrounding said first circular knockout and having regions of maximum and minimum width angularly spaced from each other on opposite sides of said first knockout along a diameter of said second knockout, said first and second knockouts having centers spaced apart such that said second knockout is defined in an eccentric relation to said first knockout whereby each of said first and second knockouts can be selectively removed to create an opening for accepting a conduit of either of said two different diameter size conduits;
• and
• (b) a second knockout structure disposed on said at least one side wall and being spaced from said first knockout structures and containing only said first knockout;
• (c) said first and second knockouts of said first and second knockout structures are respectively defined by areas of weakness along first and second substantially circular punch lines, said first punch line being completely contained within and spaced from said second punch line;
• (d) said first knockout including a first bridge member interrupting said first punch line and constituting the sole junction between said first knockout and said second knockout, said first bridge being disposed within said region of maximum width of said second knockout;
• (e) said second knockout including a second bridge member interrupting said second punch line and a pair of pseudo-bridge members which do not interrupt said second punch line, said second bridge being disposed within said region of maximum width of said second knockout and said pair of pseudo-bridge members being disposed within said region of minimum width of said second knockout;
• (f) said second bridge member and said pair of pseudo-bridge members constituting a junction between said second knockout and said at least one side wall and providing a first retention strength greater than a second retention strength provided by said first bridge member for said first knockout such that said first knockout can be removed from said second knockout without said second knockout being removed from said at least one side wall.