Question:

At which application is the safety rating CAT III / 1500 V rating needed?

Answer: 

This safety rating is used at solar farms, wind power systems, electric railways.
But also for other application in DC systems with very high requirement to safety as data centers, battery bank and e-mobility applications.

This measurement category will allow safe and accurate voltage measurement up to 1500 V DC in CAT III environment.
The product also has also a safety rating of 600 V AC in CAT IV environment.

The Fluke 393 is the world's only clamp meter with a safety rating of CAT III 1500 V and CAT IV 600 V.