I am using three different smart plugs, but all my four SonOff Zigbee Smart plugs are reporting consistently about four volts lower than the other two brands
of smart plugs
Let’s agree that none of these devices is a reliable voltage meter. Besides, the discrepancy isn’t significant and could be due to different circuit designs or local load. I’d bet that a professional measuring device would show slightly different values.
My electrical systems are “firewalled” to run off-grid to ensure that I have stable and clean voltages (set at max 220 volts) and frequency (50 Hz) . There are minor fluctuations caused by heavy equipment starting etc.
These voltages were confirmed through professional voltage readers and inverter settings. Therefore a difference of 4 Volts for the Sonoff Zigbee Smart Plugs is on a high side.
Assuming that the nominal mains voltage in your country is 220 V, the measurement results from individual smart sockets show a discrepancy of about 1.8%. This is entirely negligible. Especially considering that, for example, European standards (EN 50160) allow voltage fluctuations in low-voltage networks with a nominal voltage of 230 V within a range of ±10%, i.e., from 198 V to 242 V.
A 4 V difference is well within these tolerance limits and does not affect device operation, nor does it pose any risk or cause any losses. At my place, the voltage directly behind the meter is consistently around 235–238 V, and on individual circuits it drops slightly by about 0,5~1%.
Many thanks ks for the observations. This means calibrating such low discrepancy voltages is futile.
Thanks 