In order to ensure a selective functioning of the various SPDs, energy coordination
among the individual SPDs is absolutely essential. The basic principle of energy
coordination is characterized by the fact that each protective stage must only discharge
the amount of interference energy for which the SPD is designed. If higher interference
energies occur, the protective stage upstream of the SPD, e.g. SPD class I,
must take over the discharge of the impulse current and relieve the downstream protective
devices. This type of coordination must take into account all possible incidences
of interference such as switching surges, partial lightning currents, and so
on. According to IEC 62305-4, ‘Proof of energy coordination’, the manufacturer
must prove the energy coordination of its SPDs.