Is it adequate to put surge protection on the main electrical incomer only?
Although protection of the main incomer is certainly recommended, other services should be considered for protection against transient overvoltages (surges). For example, a lightning strike up to 1km from a building can transfer huge voltages onto overhead or underground cables – like data or telephone lines – through inductive or resistive coupling. Once transferred to the cable, transients will flow along it, seeking a path to earth and damaging any electronic components they encounter.
