Grounding of the Ubiquiti NanoStation products is important to minimise the chance of damage due to nearby lightning strikes.
A nearby lightning strike can induce damaging voltages in the POE cable running up to a NanoStation. The NanoStation has a fully plastic enclosure and mounting - so no part of it is grounded even if clamped to a metal mounting pole. Consequently - large voltages can build up that can blow the ethernet interface in the NanoStation.
This cable runs between the spare rpSMA antenna connector in the nanoStation (a convenient ground point) to a metal grounding point. A suitable point would be the metal pole on which the NanoStation is mounted - but the pole itself MUST also be grounded separately.
This picture shows a typical mounting.
Click to enlarge
This cable suits these Ubiquiti™ products: