Grid Line Settings Min/Max Extents options control the extents of orthogonal and radial grid lines.

For those grid lines that do not need to extend to the full range of the grid system, you can add to or subtract from each end of the grid line range to create "steps" in your grid systems. Have the grid line selected and click inside one of the extents fields. For instance, Max Extents. Then select the intersecting grid line to determine the extents for the grid line being changed.

You can change extends, both Min Extents and Max Extents to create isolated sections in your grid systems.