Voltage optimisers

And the heating effect will also be reduced in proportion and occur for the same additional time.

The resistive divider (between wiring resistance and kettle resistance) will apportion power in the same way for 230V and 250V.

Therefore the energy loss will remain the same as will the useful energy consumed by the heater independent of supply voltage.

I did. You might be making different assumptions about how it's being used.

NT

I don't know how you came to that conclusion. The kettle requires a certain amount of energy to boil, either more current and quicker or less current and slower. Energy lost in series resistance will be the same in both cases, but it's true that the first case will result in less loss in heating the air as the time is shorter. Hardly noticeable though.

Regulations on domestic appliances takes care of the low power factor issue in domestic premises, allowing the PSU to only charge their domestic customers for KWHs used without the complication of monitoring and charging for excessive reactive current 'consumption'.

For example, magnetically ballasted fluorescent lamp fittings must incorporate a PFC capacitor for lamps of 20W or more rating. The SL13 and SL18 CFLs made by Philips Lighting some three(?) decades back did not require a PFC capacitor to be fitted into these magnetically ballasted CFLs since they fell below that 20W limit, even allowing for a +/-10% margin of error in their 18W SL18 lamps.

It wasn't only the sheer mass of a larger magnetic ballast that a higher wattage version would have entailed that limited those early CFLs to a maximum of 18W, it was also the fact that the mandated PFC capacitor would have added further bulk (and a modest further increase in mass) to an already heavy and ugly looking lamp.

Are domestic air conditioners and heat pump heaters required to have power factor correction?

The regulations will only state that they have to meet a minimum PF figure. I don't know the details but I'm sure the manufacturers will take whatever measures are required to meet such mandatory requirements (PFC capacitors or a motor design that intrinsically has a high enough PF figure to meet the requirement without such devices).

The case of 20W and above rated fluorescent light fittings is the only one I recall but if the need to correct the PF on 20W fluorescent lamps is mandated by the regulations, you'd think other much higher wattage domestic appliances will also be subject to a minimum PF requirement. However, it's proving very difficult to track down a definitive answer to this very question other than for new regulations concerning PFC requirements on SMPSUs rated from 75W to 600W (class D).

Ian Jackson pretended :

..and simply because on the lower voltage it takes longer to achieve boiling, the longer it takes, the more time for heat to be lost. The lost heat has to be replaced as well as enough energy added to water to bring it to the boil.

The quicker it is brought to the boil, the less energy will be lost through the case of the kettle and to raising steam.

In message , Harry Bloomfield writes

Of course. [If you really want to leave no stone unturned, you could include the energy lost in getting the electricity to the kettle - ie because of the resistance of the mains wiring.]

If you reduce the power consumption far enough, a kettle will NEVER boil. A similar situation exists with vacuum cleaners, where if they don't have enough suck, they will never be able dislodge deep-seated dust and dirt. Presumably there is a limit to how much clever re-design can compensate for the effects of reduced performance.

You've not seen decent electric kettles with a metal container?

Ian Jackson laid this down on his screen :

Exactly, once radiated energy equals input energy the desired terminal temperature will never be achieved. Thus all of the energy input will be wasted in trying to achieve that which cannot be attained.

I'm not happy with my 245 to 256V supply. I use a 1kW 1500VA UPS for my computer, so when I get 1 or 2 second brownouts, it doesn't crash and corrupt the disk. When I lost quite a few LED bulbs in a short time, I tried running the lighting circuit from it. It has a built in automatic voltage regulator (it changes the tappings itself). The bulbs last about 4 times longer.

Meaning women will take even longer to get ready.

With all our heaters now off, I'm getting 222V in the lab 214V in my office.

With saving like this we can employ more administrators :-/