Measuring total current of 3 phases house on neutral line only

Hi Community,

I made a setup where I measure the current only with one clip on the neutral line of a 3 phase household connection. The measurements I get are reasonable … but somehow I ask my self, can that be right?

Does that approach brings the overall household current? What’s you view on it?

No, that is not right. What you have actually measured is the imbalance in the loads of the three phases. In an ideal world, the loads on the phases are exactly balanced, and the current in the neutral wire is zero. And then, you do not need a neutral wire at all. You can see this in the power grid that crosses the country - there are only three wires, not four.

You can prove this for yourself. Switch off everything, then switch on all the things that are on one phase, and note what you measure. Then switch everything off again, and switch on all the things that are on a different phase, and note again what you measure. Do the same with the third phase.
Add up all the currents.
Now: if you are correct and I am wrong, when you switch everything on, you will measure the current that you have written down. But I think - no, I am sure - that what you measure will be much smaller than the total you wrote down. In fact, I think it will be smaller than the largest number that you measured for one phase.

The reason is simple. When you have three loads connected line-neutral, the current flowing in one of the loads comes to the “star point” where the loads are connected to the neutral, and it splits three ways. Part flows in the neutral, part flows into the second load, and the remainder flows into the third load. Therefore, as soon as you connect another load on another phase, the current in the neutral gets smaller.

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You explanation made it clear to me! Thank you Robert.

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