50% of a SPD's efficiency depends on the quality of the installation (location & cabling). Following the installation rules listed below will optimize the protection features:
In all cases, a good equipotentiality on site is required meaning that every exposed conductive parts as well as earth connections must be connected with each other to prevent any difference of potential from arising. With a good earth resistivity (10 Ω or less), an SPD can evacuate overvoltage surges with no risk of generating secondary surges.
Electronic devices remain protected up to 30 Ω but isolating materials remain exposed to breakdowns. When the equipotentiality is not optimal, a low earth resistivity improves the efficiency of the SPD. It is also advised to reduce inductance around the SPD. Connections between the protected lines, the SPDs and the earthing bus must as short and as straight as possible (max length: 50 cm in aggregate).
Similarly, a short and straight connection between the earthing bus and the earthing connections is required to obtain a reliable LPS (length: 5 m and 10mm² cables for power lines). Otherwise, a short connection to surrounding exposed conductive parts (metallic frames, raised floors…) can be used as a complement to the earthing connection. To prevent any potential induction or capacitive effect between cables, non-protected cables must be kept away (50cm minimum) as well as the earth conductor (1m).