Measurement Categories CAT I, CAT II, CAT III, CAT IV

Measurement Categories CAT I, CAT II, CAT III, CAT IV are used to rate test instruments on their ability to resist a voltage spike, which is applied through a specific resistance. The higher the category, the more risk there that a high voltage can overload a circuit and cause electrical and physical damage. Usually, the higher the CAT (category) rating, the safer the rating.

 

 

Before looking into the various categories it’s important to understand exactly why tools are certified in particular ways. First off, when dealing with electricity, you MUST understand that the tool is either designed for a particular application or not. Many people don’t stop and think what would happen if the test probes, for example, don’t have enough insulation and too much voltage is applied to them, causing an arc. Or if too much current passes through the meter, causing it to more or less explode. These aren’t just imaginations, each one of these events has happened time and time again to electricians and amateurs alike who decided to use improper equipment to test and measure current and voltage. With that said, let’s take a closer look at the four primary measurement categories for electrical tools.

 

Distribution wiring are qualified for this group, including “mains” bus, feeders and branch circuits. Also, permanently installed or “hard-wired” loads and distribution boards. Other examples are higher voltage wiring, including power cables, bus bars, junction boxes, switches, and stationary motors with permanent connections to fixed installations