Abstract: A panelboard (2) is divided into segments for three-pole industrial frame circuit breakers (30,46). Bus bars (A,B,C) in each segment have two sets of mountng holes (18,20,22; 20,24,26,28) for replaceably receiving branch circuit connectors (34,36,38; 42,44; 58,60) for either industrial or residential frame circuit breakers, thereby enabling residential frame circuit breakers (52,54) to be installed at any segment. A dead front cover (68) having a single opening (72) encompassing all segments, and kits comprising branch circuit connectors, insulating barriers (62) and filler plates (76,78,80,84,86,88) provide complete flexibility to the circuit breaker arrangement. An auxiliary main circuit breaker (96) kit enables the panelboard to be readily converted from a lug main to a breaker main panelboard.