Each corner key assembly of an insulating glass unit is constructed of an electrically non-conductive housing having a pair of arms disposed in perpendicular relation to each other to engage with respective ends of a spacer system and a central post extending in parallel to one of the arms with an electrically conductive spring clip mounted in the post to engage a bus bar. The spring has a reversely curved portion extending from the post of the housing to lie flat against the opposed glass panes of the IG unit. Each corner key may be used as either a right-hand or as a left-hand corner key by being flipped over on itself.