How would I know when to use a 1 pole SPD or 2 pole SPD? It is always advisable to use a 2-pole unit, as surges can come through both Live And Neutral lines. More information: Surge Protection
Is surge protection devices only for lightning protection? No, surge protection devices are used for surges in the system as well due to load shedding. Factories that cause spikes in voltage, can also cause damaging surges in the system, which can cause damage to electronic equipment. More information: Surge Protection