I want to build a data acquisition device to collect electromagnetic interference signatures of household appliances on the home electrical network (power line). In fact I hope to harvest datasets similar to the ones presented in this competition.

I want to build a power line interface like this one described in the paper titled "An In Depth Study into Using EMI Signatures for Appliance Identification".

Now I seemed to have stumbled right at the start: I live in Belgium and unlike other parts of the world we have no Neutral in the mains network (single phase): we have two phases and we have 220V between the two. How should I modify this wiring diagram so that there is a high pass filter on both of the phases and make sure I don't fry the spectrum analyzer?

  • \$\begingroup\$ Even if there was a neutral connection, you still should not connect anything that isn't fully isolated. The name "neutral" suggests that there's no voltage present (with respect to ground). In practice there very often is a voltage present. It might not directly fry any measurement equipment but it can trip the GFCI (good) or shock the user (bad). \$\endgroup\$ Commented Nov 25, 2017 at 16:11
  • \$\begingroup\$ Realistically you would want proper mains isolation, that could be a transformer, this could attenuate some of the high frequencies you're interested in. Another solution could be an opto-isolator. The referenced article's schematic doesn't show any mains isolation. But then, the authors have Indian names and I've often seen that they have a lighter attitude regarding mains safety compared to engineers in the western societies. But, don't skimp on mains isolation. When in doubt: get an expert's opinion! \$\endgroup\$ Commented Nov 25, 2017 at 16:17
  • \$\begingroup\$ Thank you for the comment. I understand your concern but an isolation transformer would defy the purpose of this experiment. I assumed those 900V polypropylene capacitors serve to isolate from the mains. Do you have the same Neutral-less network in the Netherlands? \$\endgroup\$
    – JC-
    Commented Nov 26, 2017 at 22:32
  • \$\begingroup\$ No, capacitors do not isolate from the mains. If you'd hold one connection of a 100nF 900V capacitor and stick the other connection in a mains socket, you would still get a shock. Mains is AC and capacitors do not block AC. In The Netherlands we do have "fase" (phase) and "nul" (neutral) but the neutral is not connected to a (local) ground as in some countries. It is probably the same as in Belgium. \$\endgroup\$ Commented Nov 27, 2017 at 6:38
  • \$\begingroup\$ No, fase + nul + aard is what I consider standard and I called 'other parts of the world'. Belgium and Norway has fase + fase + aard as described here: In sommige oude driefasennetten in België is de spanning van de fasen ten opzichte van de nulleiding 130 V. Om 230 V te krijgen worden fasedraad en nuldraad op twee fasen aangesloten. In Nederland bestaan dit soort netten niet meer. \$\endgroup\$
    – JC-
    Commented Nov 27, 2017 at 8:43

1 Answer 1


Buying a mains isolation transformer is definitely one of the first things you should get when doing this type of testing. My though would be that you could measure the spectral density by measuring the total harmonic distortion (THD) of the current. This will give you spectral content where you want to see all the content mains frequency (ideal situation).

All about circuits has a decent enough article to get you thinking about these topics.


You could use a current transformer for mains current measurements, rectify the signal, and then do some digital signal processing (fast fourier transform) to get the harmonic content. This approach would keep your controller isolated from main since you'd be using a current transformer.


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