The cross bonding is governed by the frequencies and wavelengths to be protected against. A multipoint ground is at its best when it allows currents of many different frequencies to find a path to ground. If the system is expected to always have no more than main current present, the wavelengths involved at 50 or 60 Hz will cause the system design to become a star topology. But if higher frequencies are present, they need to be closer. In general, the spacing between nodes should be less than 1/8 of the shortest wavelength present. This will guarantee that current can always flow no matter which path it tries to take. If less than 1/8 wavelength node spacing cannot be achieved, then at least include as many cross connects as possible, as closely spaced as possible.