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Testo 760 Category IV Multimeter
I was standing at a booth at the HVAC Excellence Educators conference, and an instructor walks up, grabs a meter, and asks me, “What's the difference between a category 3 and a category 4 meter?”
Well, I really wasn't sure, but I knew that the category 4 meter is rated for more demanding conditions. So, I did some research and dug into IEC 61010-1. I found that category 3 is rated for most uses OTHER than outdoor utility connections, and category 4 meters are rated for all uses.
Courtesy of Fluke
There are also some voltage considerations and limitations to the different categories, but the primary difference is not the regular duty but the high voltage transients. High voltage transients are often called “surges” or spikes and are most common when working on outdoor transformers and distribution panels.
Rubber meets the road because a category 3 meter is likely going to do the job for HVAC use. However, if you ever work in main panels or outdoor transformers, go for a cat 4 meter.
P.S. – Fluke has a great info sheet on this HERE.
You can see more about the Testo 760 shown HERE.