Three-phase Power - recommended to measure 3 or only 1 phase? 3 VT and 3 sensor slots needed?


I have three-phase power: 3x24A, single phase is 230V. I have 2 electric power circle:

  1. circle with three-phase: (this came from power company inside)
    1.1.: L1 - 16A circuit breaker (B characteristic): refrigerator
    1.2.: L2 - 16A circuit breaker (B characteristic): working room with 0-24 on computers
    1.3.: L3 - 16A circuit breaker (B characteristic): home automation + internet + other 0-24 on stuff

(The 2. circle connected to parallel to power company’s input at the 1. circle, so the 24A circuit breaker L1 will disconnect only, if 1.1 power usage + 2.1 + 2.2 + 2.3 power usage summary will more than 24A )

  1. circle with three phase: Can disable with main switch this all of bellow circuit breakers:
    2.1.: L1: 16A circuit breaker (B characteristic): lights 1
    2.2.: L1: 16A circuit breaker (B characteristic): room sockets 1
    2.3.: L1: 16A circuit breaker (B characteristic): HIFI + TV
    2.4.: L2: 16A circuit breaker (B characteristic): lights 2
    2.5.: L2: 16A circuit breaker (B characteristic): kitchen
    2.6.: L2: 16A circuit breaker (B characteristic): room sockets 2
    2.7.: L3: 16A circuit breaker (B characteristic): lights 3
    2.8.: L3: 20A circuit breaker (C characteristic): air conditioner

I reading this nice article but few things not sure:

Q1.: Because of I have 3 phase, I needed and recommended to use 3, not 1 VT, right? So I should use channel 1, channel 13, channel 14 for VT - for L1, L2, L3 (three phase lines). Or getting 1 VT is enough, and needed to use channel 13 and 14 for 1 times calibration only? So I need 1 or 3 VT for three phase usage?

Q2.: Because of 3 phase and i have 2 circle, i also want to know the overall power usage and the 2. circle power usage, so I need to use 3x2 sensors for that, right? I can use any of free channels for that, or what is the recommendation? channel 2,3,4 for all, and for 2. circle “all” channel 5,6,7? And all with CT 100A? Or any recommendation to use CT 50A?

Q3.: So if needed 3 VT + 3+3 CT, I left only 5 sensor for measure single phase. If I have 16A circuit breaker before I measure, so not possible to use more than 16A, what is the recommended CT type for all single phase measurement? 50A or 100A?

Q4.: So for free 5 sensor slot I can use a single phase metering, like:

sensor 8: kitchen
sensor 9: air conditioner
sensor 10: HIFI + TV
sensor 11: sockets
sensor 12: lights 1

Because of I have in different phases the lights:
2.1 (L1)
2.4 (L2)
2.7 (L3)
I cannot measure with 1 sensor, right?
What is the solution? Add all light to same phase and same circuit breaker?

Recommended CT type for all 5 sensor, if I have only 16A circuit breakers?

If you need a diagram I can make it for be clear.

Thank you.

You can use one or three VTs. With one VT you will be using “derived reference” where the voltage of all three phases is assumed to be the same. With three VTs you will be using “direct reference” where the voltage of each phase is measured.

When you use derived reference (1 VT), the inputs 13 and 14 are available for CTs. Most folks use derived reference, and I highly recommend it.

You will need 3 CTs for the incoming mains. With derived reference you will then have 9 additional inputs available. I see 11 circuits listed. If you can combine two circuits by putting a CT around two circuits of the same phase, for instance 2.1&2.2 and 2.4&2.6, you can monitor everything. You say the mains are 24A, so 50A CTs should work everywhere except if you are going to put two conductors through two of the CTs, the 50A are 10mm and may not fit. The 100A are 16mm.

If you post a high resolution picture of the panel and/or a line diagram, I may be able to simplify that. I’m assuming this is a DIN setup and usually the feed to the breakers are daisy chained, so it one CT on the daisy chain feed will measure everything downstream.

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Thank you, I will use this, so I have +2 input for sensor, it’s good! :slight_smile:

0: VT and “derived reference” setting.
1,2,3 = circle 1: L1, L2, L3 for three phase main CT 100A
4,5,6 = circle 2: L1, L2, L3 for another three phase CT 100A
7,8,9,10,11,12,13,14: I will can use 8 * one phase with CT 50A (all others are less than 16A usage, or only air conditioner can be 20A too, but still not 50A)

The 2.1 … 2.8 circuit breakers is connected to three phase switch, and after this switch connected to main three phase input as 2. circle. So this 2. circle, this three phase is summary or all 2.1 … 2.8 circuit breakers power usage.

So, ordering: Eu version, 1 VT, 6 * CT 100A (for measure 2 * 3 phase) and 8 * CT 50A (for measure 8 * 16A)is fit my plans, right?

Thank you again for answer.

I would need a picture to verify what you propose. That equipment list will work to monitor 14 circuits but I can’t say it is optimum.

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I try to order the EU bundle from here:

Screenshot from cart:

I planned about this to order:

  • 1 * VT (input 0)
  • 3 * CT 100A for measure all (three-phase)
  • 3 * CT 100A for measure all others, my second circle for three-phase
  • 8 * CT 50A for others

At order page I can select 3+2 CT 100A only. Why? It’s a bug or have any reason?
Why I cannot order 6 * 100A CT and 8 * 50A CT?
I also cannot select 6x 100A in cart and also not in bundle page.

What I do wrong or not understand? Thank you.


I can add also 1 more 100A CT, but not for 12 USD, but for 15 USD.

If I order this, all will be perfect for my plan?
1 * VT
6 * 100A CT
8 * 50A CT

Or you recommends me:

1 * VT
3 * 100A CT
11 * 50A CT


Or to be sure all:

1 * VT
14 * 100A CT

Please approve my plan, thank you.

There is a limit to the CTs that can be bought at discount in the bundle. Additional are at full price.

If your “second circle” has circuit breakers larger than 50A or wires larger than about 9mm, you will need the three additional 100A CTs, otherwise you should be able to do 3 100A and 11 50A.

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I want order today this EU bundle and now cannot. :frowning:

Sorry, the store notice explains the situation.