I am at the front end of a project that, in part, measures Industrial Voltage levels: 208 Vac through 600 Vac, 3 phase. This device needs wired Ethernet connectivity.

I've got lots of options for voltage isolation, ranging from using Potential Transformers (step down transformers) for sampling the input voltage or using linear opto-couplers or even placing the A/D converters at the line side and using digital isolators to get the signals to the micro that does the Ethernet stuff.

But I was wondering if it is worth considering having all of the electronics sitting at Line Potential and simply relying upon the Ethernet magnetics as the Isolation Barrier. Worst case scenario is that the electronics is sitting at phase voltage, which can be 347 Vac (600 Vac phase-to-phase).

My gut is telling me that this is a bad idea but I wanted to get opinions from other people before dropping the idea.

I'm also not sure if I can even find Ethernet magnetic components with a suitable isolation voltage rating. Somewhere between 2500 Vac through 3750 Vac withstand voltage should be appropriate. Haven't found any Ethernet magnetics that even show Isolation Voltage in the specifications but that was after only a few minutes searching.

  • \$\begingroup\$ Go with your gut ....it's a truly bad idea to use Ethernet magnetics as mains isolation. \$\endgroup\$ Oct 12, 2017 at 0:12
  • \$\begingroup\$ "... which can be 347 Vac (600 Vac phase-to-phase)." - I assume that's 347Vac RMS. That's some 490V peak. Nominal, so before tolerances and transients, etc. Just something to be aware of ;) \$\endgroup\$
    – marcelm
    Oct 12, 2017 at 11:45

1 Answer 1


No they are not rated, nor are they safe, for continuous mains voltage isolation, let alone 600VAC with perhaps thousands of amperes of fault current. Of course something custom could probably be made, but that would be silly.

Be sensible and install a media converter/fiber link and you will be safe (but still double check the materials and construction). I have used this method for hundreds of kV.


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