Transient overvoltage

A surge is a short-duration voltage rise above the normal system voltage. Duration may be microseconds to milliseconds, but energy can be enough to puncture insulation or destroy semiconductors.

Temporary overvoltage (TOV)

TOVs last longer (seconds) and often come from faults or loss of neutral. SPDs must survive TOV without creating a fire hazard; look for TOV withstand statements on datasheets.

Why microseconds matter

Modern electronics use thin gate oxides and dense boards. A surge that an old motor might shrug off can destroy a PLC, inverter, or access controller instantly.