When power is supplied to a location there must be a means of disconnect inside or outside of the building within a practical distance of the service entrance. This means of disconnect is considered a PANEL.

At this location the neutral and ground are connected together with the grounding electrode conductor. This is the terminating point of the ground system to the service and the neutral. Should the ground and neutral be connected together at any other point downstream in the system it would provide a path for current flow through bare conductors, equipment, buildings, people or any other conductor, therefore a grounding electrode would be required at that point.(Article 250-23 and 250-24 two or more buildings from a common service.)

This need to have the neutral and the ground separated causes the need for a SUBPANEL (any panel downstream from the main panel). The method used to separate the neutral from the ground is to manufacture and sell panels that will work either way,(as a panel or a subpanel).

A new panel has packaged inside an extra screw. This screw called a bonding screw is to be installed at installation in the neutral buss, connecting the neutral buss to the panel frame or case. If the bonding screw or in some brands the bonding jumper is not connected the panel is set up as a subpanel. If it is connected the panel is set up as a panel to be used as the first panel in the installation. Panels arrive from the manufacturers with two or more busses. Sometimes these busses are connected together and have to have a jumper or bar removed to separate the neutral and ground buss, sometimes they are allready separated. A panel (the neutral and ground connected together) requires a ground electrode a subpanel does not have the neutral and ground made together.