CAT III vs CAT IV Multi-meters

Good morning, I'm trying to understand the different applications that I can use CAT III vs CAT IV Clamp on Multimeters. From what I've read online, I only need to upgrade to CAT IV if I'm using it at a utility connection, whereas CAT III can be used at a distribution connection. I don't understand the difference between the two and needed some explanation. I will mainly use this clamp on meter to check incoming power inside 480vac 3 phase industrial panels; I may need to check voltage coming out of the buss bars hanging off the ceiling of our plant as well. So for my application, is CATIV necessary? The max is 480VAC and I believe our buss bars have breakers from 100 - 200A.

Thanks,

Consider all of the applications. You can de-rate but you shouldn't over-rate. Category ratings have a lot to do with the ability of the meter to withstand brief voltage surges and offer overcurrent protection that does either or both of these things: Protect the meter. Protect the user.
Category 4, 5, and 6 meters offer some of the fastest overcurrent protection you can find. These fuses are designed to blow as fast, if not faster than T class fuses.
You don't have to get the Cat 4+ meters, Class 3 may be good enough for what you are doing. But there are many different voltage ratings at a given category. Your meter may have more than one rating. It may be rated for XXX Volts as Class 3 and XXX Volts at class 4. Which one you get depends on the short circuit current rating of what you are measuring.
Generally anything greater than 50kA should be Class 4 or higher.