A standard widely-used ground system acceptable to the US Federal Communications Commission (FCC) is 120 equally-spaced radial ground wires extending out one quarter of a wavelength (.25formula_15, 90 electrical degrees) from the mast. No. 10 gauge soft-drawn copper wire is typically used, buried 4 to 10 inches deep. For AM broadcast band masts this requires a circular land area extending from the mast . This is usually planted with grass, which is kept mowed short as tall grass can increase power loss in certain circumstances. If the land area around the mast is too limited for such long radials, they can in many cases be replaced by a greater number of shorter radials. The metal support under the mast insulator is bonded to the ground system with conductive metal straps so no voltage appears across the concrete pad supporting the mast, as concrete has poor dielectric qualities.