Overvoltage category sorts low-voltage equipment by its distance from the incoming supply, since transients are damped as they travel inward. Category IV covers the origin, such as meters and service fuses; III covers fixed distribution such as switchboards and hard-wired motors; II covers plug-in appliances; I covers specially protected electronics. On a 230/400 V system the rated impulse voltages are typically 6, 4, 2.5 and 1.5 kV for categories IV down to I.
That cheap meter is CAT II 600 V, wrong overvoltage category for the main incomer, you want CAT IV at the service head.
On a multimeter the CAT rating is a promise about surviving transients at that point in the system, which matters more than the headline voltage.
Also heard as
- OVC
- installation category
Related terms
Clearance
Straight-line air gap between two conductive parts, the dimension that decides whether a surge can flash across.
Insulation coordination
Sizing insulation and surge arresters together so any flashover lands at a cheap, self-restoring point, not inside plant.
Surge arrester
Device that clamps transient overvoltages by diverting surge current to earth, then returns to insulating.