Indication of current flow direction: variable `current` always positive

We're using the Shelly 3EM in order to measure the current coming from and fed into the grid. Knowing about current flow direction is essential for our use case.

However, we noticed, only the power-variable (Watts) indicates the direction the current is flowing (via +/- sign).

The value from the current-variable (Amperes), though, is always positive.

This is a problem, as for our use case we really only care about the current and hence only require the user to put clamps around the cables. However the power-value - and with it the indication which way the current is flowing - is only available when the voltage for respective phase is also available (as, if voltage is not available: whatever_current * 0 = 0 Watts )

Given this finding - that the current is always positive and current flow direction is only indicated when the phase's voltage is also available - the user would now also need to attach voltage for all respective phases which is more dangerous than just setting the clamps, seems unnecessary and is prone to errors.

Is there a way to receive the direction of current flow without having each phase's voltage available? We're gathering values from the JSON HTTP API.

Zitat von thgoebel

Welcome to the forum!

To your question: By rule there is NO negative current in an alternating current system. The active power only (and the power factor) are allowed to be negative, thus indicating the direction of power flow.

Thanks for your prompt reply!

From what you're saying I conclude:

- if current (Amps) can't be negative, but power (Watts) can - then the voltage must be allowed to be negative (as P = I * U), which however is always shown as positive as well

- the power factor indicates the direction of current flow

At least according to my understanding both of those conclusions do appear odd and I wouldn't expect, but potentially that's also because I'm wrongly concluding from what you were actually saying(?).

Would you mind elaborating / clarifying on that? Thank you!

Thanks once again for clarifying on this.

Just to double-check, as what I read out of it is: the value (precisely: the sign before) of the power-factor indicates the direction: withdrawal from grid vs. feed-in into the grid.

Is that correct?