My house is second to the power supply transformer and I have been observing some pretty high AC voltage levels. I previously had a really cheap multimeter and thought that the readings are off because of its bad quality. Never the less, I was getting the same voltage readouts with my early house power monitor/logger project – the energy monitoring Arduino shield. I recently received a Fluke 27 multimeter as a present and decided to again cross check the AC mains voltage, to my surprise the readings were confirmed, I was getting between 240 and 250V depending on time of day:
Voltage where I live used to be 220V before, now I understand it is being brought up to 230V in an effort to harmonize it across the EU (the UK has to bring it down from 240V to 230V levels too). Tolerance is said to be +/-10%, so my readings are on the high side, leaving no room for further fluctuation.
I decided to log the voltage levels to emoncms for couple days, here is the result:
There is a peak of almost 249V on Monday night.
Probably there is correlation between time-of-day and day-of-week plus the season/weather etc, I will leave it logging data for few months for further analysis.