There’s one scenario that some- tim

There’s one scenario that some- times confuses people trying to apply categories to real world applications. In a single piece of equipment, there is often more than one category. For example, in office equipment, from the 120 V/240 V side of the power supply back to the receptacle is CAT II. The electronic circuitry, on the other hand, is CAT I. In building control systems, such as lighting control panels, or industrial control equipment such as programmable controllers, it is common to find electronic circuits (CAT I) and power circuits (CAT III) existing in close proximity.What do you do in these situations? As in all real-world situations, use common sense. In this case, that means using the meter with the higher category rating. In fact, it’s not realistic to expect people to be going through the category- defining process all the time. What is realistic, and highly recommended, is to select a multimeter rated to the highest category in which it could possibly be used. In other words, err on the side of safety.