The length of a horizontal ground electrode is typically 10 … 30 m (33 … 100 ft).
In a shallow or rocky soil, three pieces of 10 m (33 ft) horizontal ground electrodes make good low impedance grounding. If the topsoil is moist and of low resistivity, you can use even shorter electrodes, but preferably not shorter than 6 m (20 ft) each.
A buried wire loop with a 5 … 6 m (16 … 20 ft) diameter is suitable for a single mast foundation or when arranged around a set of closely spaced equipment. Arrange at least two connection points on the loop, by making the loop out of two separate wires and leaving the wire ends above the surface.