Hello,

What's the logic of power consumption as a rough rule where if one has
the choice between the same appliance in 110v and 220v with the same
wattage where they can support both, which would they choose and why
if their priority were in lower electricity bills?

/Lizardnation

Dear lizardnation,

If the priority were lower electricity bills:

Devices with the same wattage would take the same power (by
definition) and this is generally how electricity is metered power (W)
multiplied by time kWh. So it would be best to choose on some other
criteria.

One would have to check the local electricity bill... it is
conceivable, though unlikely that if a house had two different voltage
circuits... they may be charged at different cents/kWh. This is the
case for some hot water circuits, though in my experience the voltage
has been the same.

An argument could also be made that there may be less resistive losses
with the higher voltage appliance. This is because lower current is
required to produce the same power. As neo-ga states power (W) =
Voltage multiplied by Current.
The resistive losses are calculated Ploss = square(current) multiplied
by resistance. However, such losses are likely to be neglible in terms
of your power costs due to the deliberate minimization of resistive
losses. [The reduction of such losses is the reason behind
transmission of power at very high voltages 500,000 Volts]

One reason that some homes, and many businesses use higher voltage
circuits is so that they can run higher power devices. Cabling in
houses to power outlets is generally rated for say 10 Amps, but some
higher power drawing devices eg welder may exceed this "normal" rating
and a special circuit is installed, sometimes with heavier cabling (eg
air conditioner) and sometimes at a higher voltage.

Naturally I would be happy to clarify any of the above - just select
the button.

Regards,

Laud and clear, thanks for the explanation. :-)

/Lizardnation

If an appliance is rated at lower wattage, then it will have lower
power consumption. now power=Voltage*current drawn per unit time. The
voltage is fixed for domestic supply and so the current drawn by an
appliance varies as its wattage rating. As the voltage is fixed, we
cannot choose a lower voltage device like for eg., a 110V device @
3000W to work on a 220V line- it will just spoil the device.

Hello Neo_ga,

I meant if I saw on a shelf, in a multi-voltage country other than the
US, a device available in 110v and 220v and homes had both available. 
Which would I choose?  I may be missing something. :-)

/Lizardnation