Why a single phase power meter this measure Negative VAR?

[Kiriakos GR]

Why a single phase power meter this measure Negative VAR?

Never had before a meter this capable to measure VAR and or reactive power Q.
But now its on the way, and today it landed at Netherlands according to tracking.
 
Today I did a bit of internet search, so to discover of how many bench top power meter support VAR measurement?
And I came across of the above question. 

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The theoretical answer this is easy:
An capacitive load will drive the VAR to the negative side.
An inductive load (AC motor) this will drive the VAR at the positive side.
An resistive load this will disappear the VAR = 0 

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Now lets talk about single phase power meter regarding electronics implementation.

First example: You might have at hand an instrument this using a TFT large screen, in which it offers the convenience to have plenty of space so to display detailed description, of any single electrical parameter.
At such an screen, they are chances to see the minus symbol in-front of the VAR measurement.

Second example: You might have at hand an instrument this using broken LED windows, at a number of three, four, six or more.
These instruments does not include the minus symbol, but instead you may gain enough information due the Low Value at the Power Factor (LED window)     
 
When we are after to review and or measure, electrical energy at stand-by power mode (of any Switching Mode Power Supply), it is expected power factor this to be very low.
And or, VAR to be measured as negative.
All Switching Mode Power Supply (with out exception), at their Stand-By state, they are mainly an capacitive load.

Note: The instrument with tighter accuracy specification at Power Factor, this will deliver and a more accurate calculation of VAR.
This is why it is of HIGHEST importance, to buy only instruments which comes with a Calibration Certificate. 

[overvolt]

Note: The instrument with tighter accuracy specification at Power Factor, this will deliver and a more accurate calculation of VAR.
This is why it is of HIGHEST importance, to buy only instruments which comes with a Calibration Certificate.

Indeed, and even VAR as a portion of energy measured in Watt, this will be within accuracy Class of the power meter it self.
0.5 Class for energy =  Watt and Var identical measuring error tolerances.

When there is power factor detection error, both Watt and VAR will be in error.

[Kiriakos GR]

Everfine brand in China, has two interesting advice's within their own User manual, about broken LED display power meter.

a) Being limited to display digit, when the active power is negative, the minus is not displayed (negative polarity can be judged depending on the power factor).

b) (This tip, is about negative power detection), and the suggestion is to reverse the wires of the Load, and OR to reverse the wires of the Voltage input.
Example: You set power alarm at 10W or higher, but the alarm is triggered all times, because it is measured as Negative value.
 
About b) I have seen that with my oscilloscope, when I was measuring phase difference.
By reversing input wires, I was able to correct voltage-leading-current (waveforms), at the screen of my oscilloscope.
(These are tips related to proper wiring of a single phase power meter)

This is of why I did buy this little gadget = Mains wall-plug Phase detection
https://www.ittsb.eu/forum/index.php?topic=1830.0