Similar to ACA, we're just measuring potential or voltage. Common ranges of AC voltmeters are from millivolts to kilovolts or .001 V to 1000's of ACV...self contained voltmeters have a max of approx 600 ACV. Any thing above that...yep, you guessed it, we have to use an external Potential Transformer or PT.
I think of ACV as lightining in a small place. This is why the mfg puts a limit of 600 ACV to be a self contained meter. ACV wants do jump to the nearest conductor when there is too much of it in a contained space. They would call this the "dielectric strength" of the construction of the meter. How much insulation or how much ACV it can handle at one time. They meet specific requirements and guide lines set for by most industry codes and are described and stated in the specifications for each mfg. So we want to measure 1500 ACV or 1.5KVAC. We would use a PT of 10:1 or 1500: 150. Yep, you're way ahead of me..the meter will have a scale of 1500 ACV (1.5KVAC) and an input of 150 ACV. This is a PT rated meter...you're well on the way now...very similar to the ACA meters.
