1. Lightning Fundamentals · Page 4 of 6
How Surges Enter a Building
Conduction, induction, and earth potential rise explained for facility engineers.
Conductive coupling
Surges travel along power conductors, metal pipes, and cable shields into the installation. Service entrance conductors are the classic path for power-line SPDs.
Inductive coupling
Changing magnetic fields around a lightning channel induce voltages in cable loops. Large loop areas between phase and PE create higher induced voltages.
Earth potential rise (EPR)
When lightning current enters earth, local ground potential rises. Equipment bonded to distant earth references can see destructive potential differences.
Practical defense
Bonding, short SPD leads, equipotential connections, and staged SPDs reduce all three coupling mechanisms.