kWh meter

"How do you calculate CT on an energy meter?

Let's assume you have a 480 3-phase service. The installed CT has a ratio of 400:5 and the PT has a 4:1 ratio. The CT multiplier would be 80 and the PT multiplier is 4. Since a watt = amps x volts, the watthour meter multiplier, in this case, would be 80 x 4 or 320."...

read this... https://peakdemand.com/instrument-transformers-and-the-meter-multiplier/

Rated current 0,25-5(80A). What does this 80A means?

It means 80 amps in the line produces 5 amps from the CT. In other words, the CT secondary has 16 turns resulting in a 1/16 current ratio.

Would this kWh meter be undersized because I have 300/5A?

If you just use the 300/5 in place of the 80/5 CT, the kWh reading will be 80/300 of the true value.

(As Randall has noted, the datasheet alludes to an adjustment for CT ratio. You might want to investigate that.)

I thought so, you just confirmed my opinion. Thx a lot!!

From my meter testing days the rating brackets meant the maximum current the meter could handle without going out of tolerance, eg 5-20A, 10-80A, 10-100A so the meters nominal 100% current is the first figure and the second one is the over range current where the meter is still within nominated values.

The meters were tested at, nominal current 1.0 PF, nominal current 0.5PF, low start current ~12W and the nominal over range current. The meters readings were compared with a calibrated standard meter.