Surge protection failure is rarely the result of no protection. It is almost always the result of the wrong protection — a device selected on availability or price rather than on the four engineering parameters that determine whether it will perform when called upon. The IEC 61643-11 standard exists precisely because under-specification is the industry's most persistent and costly problem. The parameters that matter:
Installation category — Type 1 at the service entrance, Type 2 at distribution level, Type 3 at the point of use. Each serves a distinct function. Combining them incorrectly leaves gaps that a surge will find.
Voltage protection level (Up) — the maximum voltage permitted through during a surge event. If Up exceeds the withstand rating of connected equipment, the SPD is certified and useless simultaneously.
Nominal and maximum discharge current (In and Imax) — defining how much surge energy the device handles repeatedly and at peak. An undersized device degrades silently and fails without warning.
Short-circuit current rating (SCCR) — a parameter frequently overlooked during specification and critical to installation safety.
Environmental conditions compound every one of these variables. A device correctly specified for a controlled indoor environment will perform unpredictably — and potentially dangerously — in a high-humidity or high-temperature industrial setting.
The right SPD is an engineering decision made before procurement begins. Everything else is a gamble dressed as a specification.