3 wire 3 phase monitor with two or three CT's?

Hi, have Just installed my flukso v2, it's been running for about 24 hours now :

Second major question,

System is as described below, when I first setup I selected 3 phase in the sensor setup, with a reduced voltage as suggested by Bart in another post. However this yielded very high 10kw load for a consumer that I know is rated at 4kva.

When I spilt the three phases out I see approximately correct wattages per phase

This lead me to do a bit of reading around and I came across this document


Bart I would really like to get to the bottom of the correct way to measure 3 wire 3 phase systems that are prevalent in Belgium but also the USA and Japan ( apparently ). however this is beyond my limited electrical engineering and mathematical skills.

Regards Keith.

System is Belgian and setup is as follows : 3 wire 3 phase 220 v line to line voltage.

3 phase 3 wire unbalanced both single phase ( line to line ) and three phase mixed inductive and restive loads
Line to line voltage is 220v Line to earth voltage 128v

One 50A CT per phase, each recording separately at the moment, ( more of that in another post ).

Solar Inverter Segregated from consumer load measured using pulse output.

Main consumer is a 4kva single phase (line to line) heat pump,

icarus75's picture

Hi Keith,

A 3-phase, 3-wire setup is a tough one read out accurately when only using current clamps. As explained in the article you refer to, a 3-wire system can indeed be read out with a two-meter setup, provided that each meter consists of a current and voltage measurement (incl. phase angle). Since we're only measuring current with the CT's, any measurement for this 3-wire system will be approximate. The added measurement difficulty compared to a 3-phase, 4-wire system is that in the former case the line current is different from the phase current.

For a 3-phase, 3-wire 230V system being read out via current clamps, I would suggest putting a clamp on each mains wire. In case of a resistive (i.e. cos phi equal to 1) balanced three-phase load, a phase (=line) voltage setting of 133V will result in a correct reading. A resistive single-phase load will read approx 15% high and an equal resistive loading of two phases will be read 8% on the high side. Since most households will have both single- and three-phase loads present, lowering the line voltage by 8% (= 122V) should be a good trade-off.


llksta's picture


Thanks for the response,

I started as you describe but in the end I resorted to a crude calibration using the main household meter to bring the line voltage down. I now have about +\- 5% accuracy.

Still that has been enough to spot a problem with my heat pump installation that would have wasted several hundred kwh over the year.

icarus75's picture

Hi Keith,

1/ What line voltage did you finally configure on the FLM sensor page?
2/ I'm intrigued by your heat pump story. Could you tell me what anomaly you were able to track down and how went about doing this?