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ATM90E32AS for 3Phase3Wire system

I am considering to use ATM90E32 for polyphase measurement of a 3-phase 3-wire system (3P3W, Y).

But, I am unable to find any reference diagram for 3-phase 3-wire system.

Can you someone please share any source material or point me in a right direction.

Welcome, Anurag, to the OEM forum.

I’m not sure what you want. You say you have a 3-phase, 3-wire system:

What does the “Y” mean? If you mean star connected, you have a 4-wire system. Your connections can only be in delta if you have a 3-wire system.

Also, what do you want from a “reference diagram”? Have you looked carefully at the Atmel website?
(it took me under a minute to find this: If what you want to know is not in there, I would be extremely surprised.

Hi Robert,

Sorry for the typo.
I meant delta connected 3-wire 3-phase system.
And yes, I have figured out the same reference material.


So - what is your difficulty? On page 9, there’s an application circuit diagram, showing the voltage inputs and current inputs, and optical isolation on the digital outputs.


The GND connection shown means that the whole circuit up to the opto-isolators on the outputs is live to Phase B. You must not test nor work on this circuit as drawn unless you are experienced and competent to work on live apparatus.

How can I do connection with 3P3W.
As there are only two wires A & B, which are connected.
How should I connect B, as those MCU pins are connected to GND.
Does that mean I don’t have to connect one of the wires?? If yes, then how do I determine which one not to connect??

Have you read the page in ‘Learn’ about 3-phase power? When measuring any power, one of the very basic facts is this: you need one less wattmeter than the number of wires. Now one channel of your M90 counts as a wattmeter, so the diagram is perfectly correct: it treats Phase B as the reference or common wire (and you don’t measure the current in that one) and it measures the currents in phases A & C, and measures the voltages between A & B and C & B. And this is why I warned you about safety:

The “GND” on that diagram is LIVE to phase B. If you do not understand that, you risk electrocuting yourself.

I am a Chartered Electrical Engineer, I don’t think you understand the danger that you are putting yourself in.

If you must continue with this project, then I think you must use an isolating transformer to measure the voltages, and not make a direct connection to the mains electricity. That will be expensive, but how do you measure the cost to your family if you lose your life?

I think you need two of these: to replace the direct connections via the chains of resistors R3 - R10 and R25 - R32.
Connect the BRN wire of the first SPT-0375 to Line A.
Connect the BRN wire of the second SPT-0375 to Line C.
Connect the BLU wires of both SPT-0375 to Line B.
Connect the WHT wire of the first SPT-0375 to the VAP input (Pin 13) of the M80.
Connect the WHT wire of the second SPT-0375 to the VCP input (Pin 17) of the M80.
Connect the BLK wires of the both SPT-0375 to GND.

Thanks for your response.
I think its more feasible to use Delta to Star transformer, then feed it to IC.