Electricity voltages: some key points
1. When the present voltage standards were set, probably in the 1960's or 1970s, there were very few appliances with a standby function: they were either on or completely off. Now we live in plugpack and remote-control heaven, and even radio cassette recorders (with no radio and no tape playing) have a live internal power supply if they are plugged into a live power point.
2. The industry has found from experience that it must maintain 225.6 volts to keep customer complaints about low voltage to an acceptable level. Virtually all appliances will work efficiently, do the job they were designed for, and live a lot longer if run at 230 volts. And use up to 33% less power than at 254.4 volts (see my experiment).
3. On cold winter evenings, or in a heatwave when every air conditioner in the suburbs is switched on, the only way for the last customer to get an adequate voltage is for the power company to turn up the voltage supplied to the pole transformers. In this situation, customers near the transformer will experience higher than normal voltages. The industry regards 254.4 volts as the safe upper limit at the point of supply to these households, in this circumstance.
4. For all other times of the year, probably 95% of the time each year, the voltage could be turned way down, and still deliver a perfectly adequate voltage to the "end-of-the-line" customers. For average load conditions, 240 volts should be the maximum voltage in any part of a nominal 240 volt supply (called a "low voltage" or "LV" line in the industry). For a lightly loaded LV circuit in the pre- dawn hours each day, all customers will get all the power they need if the secondary voltage at the transformer is adjusted down to about 235 volts. If this were done, the industry could not be accused of profiteering, or risking public safety. The point here is that the finite risk associated with 254.4 volts is only acceptable when it is absolutely necessary at peak load times, in order to deliver about 230 volts to the end-of-line customers.
5. A network fine-tuned as indicated above would result in milions of dollars saved by customers through reduced power bills, reduced spending on replacement appliances, and quite probably, after some years, reduced home insurance premiums.