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.

  • \$\begingroup\$ Something as this ... and a few other devices (smps isolated power supply) ti.com/lit/ds/symlink/… \$\endgroup\$
    – Antonio51
    Mar 16, 2022 at 21:45
  • \$\begingroup\$ smps isolated supply ... something as this xppower.com/product/IML02?m=IML0205S05 \$\endgroup\$
    – Antonio51
    Mar 16, 2022 at 22:20
  • \$\begingroup\$ Various manufacturers have mains metering chips that will simplify your task. Analog Devices have such devices. \$\endgroup\$
    – Kartman
    Mar 17, 2022 at 0:22
  • \$\begingroup\$ Do you already have +5V and -5V or similar for op-amps? \$\endgroup\$
    – rdtsc
    Mar 17, 2022 at 14:53

1 Answer 1


I would consider using three 480V primary signal transformer. Using it on 220 would not be a problem as you will not be loading it. They are not super expensive, agency approved and I believe they would work nicely in your application. The turns ratio may not be exact between units but you can calibrate that out. Your circuit could empirically determine the voltage by reading the output voltage and setting the gains in your circuit accordingly.


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