Device failure

An irreversible change in characteristic, resulting in an inability to perform as intended.

Comment: In the context of surge protection devices (SPDs), the following examples of "device failure" are given in various IEEE C62 documents:

• shorting or opening of any component;
• failure of a component in any one stage of a multistage unit;
• changes of nominal varistor voltage exceeding 10% between pre‑ and post‑tests in the 1 mA d.c. test;
• overheating which results in a hazardous condi­tion;
• irreversible change in characteristics of any component beyond the specifications limits.

Two types of devices are found on the market: One type includes a internal fuse or thermal cut‑off, or both, disconnecting the failed SPD component while leaving the load energized (protection is lost for the next surge but operation of the load is maintained). The second type includes a internal fuse or thermal cut‑off, or both, disconnecting a failed SPD component, and the load (protection is maintained but operation of the load is inter­rupted). Forewarning the purchaser about this choice by suitable wording on the package is highly desirable.

Source: UIE Guide to Quality of Electriical Supply for Industrial Installations, Part VI: Transient and Temporary Overvoltages and Currents