I want to hack my electrical distribution board a little, to measure the energy used by each circuit.

Thus, I want to use a little arduino or maybe a raspberry pi and plug it to my circuits to take measures (I assume I should use things like ampmeter or voltmeter). Then I could make charts about what use energy the most in my home (and eventualy point energy leaks).

Unfortunately, I have less-than-basic knowledge about electricity, so I don't have a clue about how to measure energy.

So here are my questions :

  • where and what should I plug to my circuits ?
  • how many measures would be enough to be valuable ? (one every millisecond ? second ? hour ?)
  • would this system consume a non-negligible amount of energy ?

EDIT : as Will Dean stated, I should start with something small. Please consider this question to apply to a simple plug, and not an entire electric panel :-)

FINAL EDIT : I have to admit this seems way too dangerous for me since there is too much information I don't know about the electricity way across my home. So the final answer is : I give up for now. Any advice to how to teach myself is really welcomed

  • 2
    \$\begingroup\$ So you want to build your own version of a kill-a-watt? \$\endgroup\$
    – PlasmaHH
    Feb 8, 2017 at 16:11
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    \$\begingroup\$ I have less-than-basic knowledge about electricity yet you want to hack my electrical distribution board. You do realize that you really have to know what you're doing here since this is mains you're dealing with. You could kill yourself/ set your house on fire. I hope you do realize that appropriate knowledge is required in this case. Do what PlasmaHH suggests, buy one or more plug-in power meters (kill-a-watt), those are safe to use. \$\endgroup\$ Feb 8, 2017 at 16:13
  • \$\begingroup\$ You cannot accurately measure power without measuring voltage, and it doesn't really sound like you're ready to be connecting mains electricity to your Arduino circuit yet. Start slower - measure the power consumption of a flashlight or something safe like that. \$\endgroup\$
    – user1844
    Feb 8, 2017 at 16:13
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    \$\begingroup\$ Its not only dangerous, it may be illegal depending on where you live. Also, it doing so will probably invalidate any insurance agreements you have so be wary. \$\endgroup\$
    – Voltage Spike
    Feb 8, 2017 at 16:44
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    \$\begingroup\$ That's what the kill-a-watt type devices do, monitor one plug at a time: amazon.co.uk/UEB-Electricity-Analyzer-Overload-Protection/dp/… (generally you buy one and move it around your devices. Doesn't tell you about light circuits or wired in things like heaters and cookers.) \$\endgroup\$
    – pjc50
    Feb 8, 2017 at 17:01

2 Answers 2


With admitted 'less than basic' knowledge about electricity, that means you must not make any connections to the mains on your board.

What you want is a clamp-on current transformer on each wire you want to monitor. This usually takes the form of 2 C-cores, with either a winding round one of them, or Hall sensor or two embedded in them. These will isolate the mains from your low voltage measurements. I am not going to recommend any particular part numbers, but at least you know what to search for now.

Most people doing this sort of thing would assume constant mains voltage, and unity power factor, and not measure it. It's only worth doing if you are making metering-quality measurements, which it sounds like you're not.

  • \$\begingroup\$ Thanks for your answer. Which wire are you referring to if they are outside of my board ? \$\endgroup\$ Feb 8, 2017 at 16:37
  • \$\begingroup\$ The wire between your board and the circuit you wish to measure the consumption of. If the wires from the board are buried or in cable with the neutral, it would be safer and easier to do the monitoring at the appliance end rather than the board end. \$\endgroup\$
    – Neil_UK
    Feb 8, 2017 at 17:58

Non-intrusive way of monitoring the meter: https://github.com/dkroeske/emon-server

That relies on having one of the modern kind of meters which has a flashing light on it. The light flashes exactly once for each watt-hour consumed. Count the flashes and you can estimate power consumption over time.

The clamp meter approach (Neil_UK's answer) relies on identifying the individual circuits leading out of the board, separating the conductors (if they're not already free of the outer insulation, this will require powering down and very careful cutting), then applying a clamp meter or current transformers.

There's also this which looks interesting, but not very beginner accessible: http://ieeexplore.ieee.org/document/5433631/


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