In order to calculate true RMS phase-phase voltage of a 3-phase delta 3-wire industrial utility, I have been using Zettler Magnetics AHI02516 as step-down/isolation transformers, along with some voltage-divider, DC-bias, and op-amp circuitry to condition the voltage fit within the ~0-3.3V ADC on an Arduino Due. This has worked well for measuring up to 208V, with my only complaint is that the Zettler transformers have a larger size footprint than I'd like.
I've been tasked with upgrading this system to work for both 208V and 480V (and 120V, in a single-phase configuration). My first approach was to find a different PCB-mounted transformer that can support 480V (the Zettler model maxes out at 240V) but I couldn't really find any suitable options. I also did a lot of research and found information about what I should NOT do, such as putting two 240V-rated transformers in series. My second approach was to consider ways I could remove the transformer entirely, but I'm not sure that's possible since I'm measuring phase-phase voltages that therefore do NOT have a common "ground" in reference to the ADC/MCU. I was looking at some optocoupler information but I don't have enough experience with those devices to make the call whether they would perform the same way (or be safe as well).
To sum it up, I'm looking for a (relatively) clean & compact solution to read in (a scaled-down version of) the 3 480V waveforms of the 3-phase system.