Hi,

I've noticed since I got this unit that the figures are not accurate at all.  For example, I'm currently monitoring a shed that has a pump and a light running 24/7 along with some control gear.  Normal readings is around 50W.  This is shown in the image below.

Once an hour another pump kicks in for 5 minutes.  When this happens, we jump down to around -13W as shown below

This is obviously incorrect regardless of the polarity of the current clamp.  Any ideas?

This is a sub circuit, and does not generate power at all.

Cheers,

Paul

Hi:
Firstly, please confirm that your system connection is WYE(star), not delta.
The meter only works for the system of star connection, not for the delta system.

After this, according to your description, the most possibility is the phase mismatch.
For example, you clamp the CTb(phase B) to the wire of phase A.
Because the power is active power.
Active power =voltage * current * power factor
and if you clamp CTa to the wire of phase B, it will cause a negative power factor when some inductive load(such as pump) is online.

So please check this carefully.

If you want to confirm the accuracy of the meter, the most simple way is this
1 connect UA UB and UC together to the same voltage input, such as the voltage of phase A.
2 clamp CTa, CTb and CTc to the same wire of phase A either.

Then compare the power reading of the three-phase .

Of course, this method is to compare the consistency of three-phase reading, but it will also reflect the accuracy to some extent.