I'm thinking about using the Allegro ACS712 current sensor for measuring house equipment current consumption (for example TV). The issue I'm facing is that my house energy supply is built around two 110VAC phases. My equipment works with 220VAC but not in Live-Neutral configuration, but in Main1-Main2 configuration.

Having the two connections "active" confuse me a bit... I don't know how to proceed. Should I use two sensors, one for each main? Should I measure only one cable? Will the equipment current flow from only one main or from both of them?

Any guide will be appreciated.

Thanks a lot!


This image represents what I want to do:

Block diagram for mains power current measurements using ACS712

Also, the values you see stated were measured by my multimeter. Maybe this helps to sum up what I was trying to say and reduce confusion.

  • \$\begingroup\$ It would help if you could draw some kind of diagram. Not necessarily a schematic, but just something showing which wires are connected to what and where you propose to put the ACS712. But basically, if your equipment does not connect to neutral, then the current flowing in the neutral wire will be 0 and does not need to be measured. The current flowing in the main1 and main2 wires will be equal. So it sounds like you only need one sensor (but it would be nice if you could add a diagram to your question). \$\endgroup\$ – mkeith Sep 30 '18 at 17:51
  • \$\begingroup\$ The 220V system can potentially give you an electric shock. When designing electronics that connect to 220V, a lot of safety needs to be engineered into the system to minimize the chance of people getting electric shocks (which could potentially be fatal). So I would caution you that there is a lot you will need to learn if you want to do this safely. I am not trying to discourage you from doing it, but I am encouraging you to learn as much as you can about isolation principles for mains connected stuff. Not my area of expertise either, by the way. \$\endgroup\$ – mkeith Sep 30 '18 at 17:55
  • \$\begingroup\$ Hi guys! Thanks a lot for the answers. I'll add some king of schematic of what I thinking. Also I couldn't agree more with you, is something I'll love to achieve but is by far very dangerous... my goal is not to compromise any person or equipment. And is just a personal proyect... nothing commercial. \$\endgroup\$ – ferdinandcinzano Sep 30 '18 at 18:25
  • \$\begingroup\$ If that is a photo of the exact module you plan to use, I am concerned that the clearance between low-voltage and high-voltage side of the PCB is too small. Note that the (GND?) fill copper on the top layer of the board extends very close to the screw terminals. Try to find a module specifically rated for 240VAC or higher. A stray wire or something could lead to the low-voltage side of PCB being energized at line voltage. \$\endgroup\$ – mkeith Sep 30 '18 at 19:32
  • \$\begingroup\$ Yes... thats the arduino compatible module. The gnd plane is too near the measure connection. I beleave they designe it for DC low current measure (acs module has a 5Amp, 20Amp and 30Amp version, all been able to measure AC/DC current). \$\endgroup\$ – ferdinandcinzano Sep 30 '18 at 22:16

It sounds like you have a standard North American "Split Phase" electrical supply as supplied to most residential homes. As you mention: you have two "Line" connections plus a Neutral.

Most of your loads are 120 Vac and come from one of the Line conductors to Neutral. The remaining loads are 240 Vac and come from both of the Line conductors.

What you need to measure depends on what you are trying to measure. There are a couple of possibilities: you are trying to measure the current consumption of the entire household OR you want to measure the current consumed by only a single load.

If you are trying to measure the current consumed by the entire household, you have to measure the input current on BOTH of the Line conductors. This is because most loads return to Neutral but the remaining loads return to the other Line conductor.

If you are trying to measure the current consumed by a single device, you need to have current sensors on the total number of active power conductors (Line & Neutral) minus one.

In other words, if your load is strictly 240 Vac with NO Neutral connection, you need only ONE current sensor. OR: if your load is strictly 120 Vac with no connection to the other Line conductor, you also need only ONE current sensor.

However, if your load is something like an electric clothes dryer or electric range, you need TWO current sensors. That is because part of the load is between the two Line conductors, the remaining load is between either of the two Line conductors and Neutral.


Based on your revised question, I would say that you need only ONE current sensor. It doesn't matter which Line conductor the sensor is connected in series with.

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  • \$\begingroup\$ Great! Thank's for your answer!! I don't have good knowledge of AC distribution. I'll try to get as much data as possible and test the idea. Making sure nothing bad happens. Regards :)! \$\endgroup\$ – ferdinandcinzano Sep 30 '18 at 22:20

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