merlin gerin pm700 power meter

Merlin Gerin PM700 power meter


I wanted a small unit to plug into, or between two, mains feed cables to measure voltage, RMS current, power factor and harmonic distortion.

I found this Merlin Gerin PM700 power meter at a fair price on ebay and decided to find some current transformers and hopefully be able to fit it all in a small box.


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I wanted to build the unit for continues 32 A load, so that it could be used in larger installations. So I had to make some 16 A to 32 A CEE adaptors in order to use it with my more regularly used 16 A fed items.


Merlin Gerin PM700 True rms up to the 15th harmonic

on three-phase (3P, 3P + N)

two-phase and single-phase AC systems

32 samples per cycle


Current transformer 30 A / 5A (2 turn)


29th March 2016

Finding a box among those I had in stock turned out this aluminium enclosure where everything would barely fit. I really wanted this to be as small as possible, so I took the challenge of fitting it all into it.



It is a wonderful tool that provides accurate measurements of voltage, current, power consumption, power factor and harmonic distortion. It will make a great addition to bettering the power factor of Tesla coils, to find out what kind of corrections that work the best at different loads.

Unfortunately it requires externally power from 230 VAC, I could just have built this in to take from phase and neutral, but that would render the unit useless with a variac, at low voltages, in front of it.


30th August 2016

First demonstration of how it is built and a test with a pure resistive load from a 9 kW electric heater.

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