2. Surge Phenomena & Overvoltages · Page 4 of 6
Common-Mode vs Differential-Mode Surges
Know which path the surge takes so you choose the right SPD configuration.
Differential mode (L-N)
Voltage appears between live conductors. Sensitive electronics often fail first in this mode.
Common mode (L-PE / N-PE)
Voltage appears between conductors and earth. Insulation to chassis and communication ports is stressed.
SPD configurations
1P+N, 3P, and 3P+N assemblies provide different combinations of L-N and L/N-PE protection paths. Match the configuration to the supply system (TN-S, TN-C-S, TT, IT).