Product recommendation: 3-phase 240V (120V, 120V, 120V, Neutral)

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Hey there, I’m from Mexico and I want to install an energy monitor in my house. Here in Mexico we use 3-phases for HVAC system and mono-phase for the rest of the house. The currents we get from the utility company are 120V, 120V, 120V and Netural (total 4 cables). For the AC we use 240V, but for the rest (light, computers, TV, kitchen appliances, etc) 120V. I know is strange but this is how electricians set the energy here. Can anyone recommend me the right product for me?


Welcome, Alejandro, to the OEM forum.

What I think you have is in fact a common 3-phase electricity supply. But I am sorry - you do not have the voltages correct. It is impossible to have 120 V Line - Neutral and 240 V Line - Line. I think you will have 127 V Line - Neutral and 220 V Line - Line.

What do you want to measure, exactly? If you only want the power and energy consumption for the whole house, then you have two choices:

If you are happy to have a solution which will be slightly less accurate, you can have an emonTx with one a.c. adapter to measure the voltage and 3 × current transformer to measure the current on each incoming 127 V line. You will need the 3-phase sketch uploaded to the emonTx. There will be a small inaccuracy because the software will measure the voltage of line 1 and assume the voltages of lines 2 & 3 are the same - which might not be true.

If you want to measure individual circuits, or you want better accuracy for the whole house, then you will need 3 × emonTx, using one for each incoming 127 V line. Each emonTx will need an a.c. adapter to measure the voltage and 1 × current transformer to measure the current on the incoming 127 V line. The three together will again give you the total power and energy for your house. Each emonTx has 4 current inputs, so you have 1 measuring the main current and 3 more on each emonTx that you can use to measure the current on individual 127 V circuits on that phase. (You cannot get the correct power if you mix current and voltage on different phases.)
If your electricity distribution board allows it, you might be able to bunch a group of individual circuits on the same phase and measure the total power for the group with one current transformer.

You will also need something to record the data so that you can view it. For that, you need an emonBase. This is a Raspberry Pi equipped with a radio receiver to receive the data from one or more emonTx.

And you will need a programmer and cable to set up the emonTx, and a power supply for your emonBase.

Hi Robert, thanks for your response.

Correct, here in Mexico sometimes we call it 240V, but it’s true, is the same as 220V.

I want to try first to measure my Air Conditioner as it is in a separate breaker panel outside my home (inside a garage closet). This breaker panel has 3-phase 120V and feed 5 Air Conditioners. I would like to measure the total amount of current of the whole breaker panel, and also each of the Air Conditioner circuit (5). So total I think I will need 3 CTs (100A) for mains and 5 CTs for the Air Conditioner circuit (70A).

Where does the main cable come into your house? How does the garage breaker panel relate to the breaker panel for the rest of the house? And what is the distance between them?

How are the 5 AC units connected to the three phases? Is each individual unit 127 V single phase (L-N), or 220 V (L-L)? The reason for asking is 5 × 70 A at 127 V is about 45 kW, and that seems a lot.

(What I want to do is give you the most economical option for the whole house - at the moment, it looks as if you need 2 × emonTx with the 3-phase sketch for the AC system alone. Plus it might be necessary to make a small modification to your emonTx’s to allow the 4th channel to read more than 16 A.)