The so-called energy coordination means that when multiple levels of SPDs or protective elements have different discharge capacities and are used together, the lightning current must be reasonably distributed to ensure that the SPDs or elements with smaller discharge capacities are not damaged.

As shown in the figure below, SPD1 has a high discharge capacity and a high residual voltage, while SPD2 has a low discharge capacity and a low residual voltage. To achieve optimal protection (high discharge capacity and low residual voltage), both SPD1 and SPD2 are used. However, in reality, lightning current does not always flow as expected, with most being discharged through SPD1 and a smaller portion through SPD2. If energy coordination is not achieved, SPD2 will be damaged by sharing the excessive lightning current.

Similarly, for signal SPD, there is also the problem of energy coordination. If the energy cannot be coordinated, the TVS will be easily damaged.

Power SPDs require a 5-10m distance between the two stages during installation to achieve energy coordination. Signal SPDs typically incorporate a coupling resistor between the GDT and TVS, also for energy coordination. Because resistors dissipate power, they are only suitable for signal loops with low current.