Most panel equipment that is manufactured for the residential market has only one buss bar installed at the factory. If you look you will find that the factory installed buss bar is bonded to the panel cabinet when the panel is used as service equipment. The service equipment is the one place were the connection between the grounded current carrying conductor (that most of us call the neutral) and the enclosure is supposed to occur. Service equipment is also the place were the Equipment Grounding Conductors (EGCs) are connected to the utility's grounded conductor (neutral) via the grounded service entry conductor (neutral). When this type of panel is used as a feeder supplied panel instead of as service equipment then additional buss bars are added which bond through their mounting screws directly to the cabinet. The main bonding jumper screw or strap is then removed from the factory installed buss bar to leave it insulated from the equipment enclosure.

Some designs, such as GE, have a bridging bar that serves as the connection between the halfs of the buss bar located on each side of the panel. One side has the main bonding conductor installed in the form of a screw. As long as the bridging bar is in place then both sides of the buss bar are functioning as one buss and are bonded to the panel cabinet. If that panel is to be used as feeder supplied equipment rather than as service equipment the bridging bar is removed. The bar on the bonded side is used as the Equipment Grounding Conductor buss bar. The bar on the unbonded side is then used as the grounded conductor buss bar. The drawback to that design is that one of the conductors for each circuit has to be routed to the opposite side of the cabinet.

Other panel equipment is factory equipped with separate buss bars for the grounded current carrying conductors and the Equipment Grounding [actually bonding] Conductors (EGCs) in order to facilitate the panel being used as a feeder supplied panel rather than as the service equipment. Such panels are not commonly used in the residential market. When panels that are factory built for dual use are used as service equipment the two types of conductors may be on separate buss bars but they are connected to each other by the main bonding jumper that bonds the grounded current carrying conductor buss bar to the panel cabinet that is serving as the service equipment enclosure. When that same piece of equipment is used as a feeder supplied lighting and appliance or power panel board the only change that is needed is to remove the main bonding jumper.