Why is alternating current used in homes?

1 Answer
Aug 7, 2018

Because it is easier to distribute over large distances with relatively low losses, and it is a bit safer for the same voltage if touched.


Alternating current is used in most electricity distribution systems for several reasons, but the most important one is the ease with which it can be transformed from one voltage to another.

DC is very much more difficult (and expensive) to do this with.
(To transform DC, electronic circuits are used to generate AC which is then transformed with a transformer and rectified back to DC.)

Huge amounts of AC power can be transformed to almost any desired voltage, with very low energy loss, using an electric transformer (coils with their magnetic fields closely linked).

All "room temperature" conductors have resistance, so they heat up when carrying current.

The heat (transmission loss) generated by this is proportional to the square of the current, and to the resistance:

Energy #= I^2R#

To minimize energy loss it is important to keep both resistance and current low, with low current being particularly important because it has an exponential effect on losses.

Power #P = V*I# (volts multiplied by amps) so for a given power, voltage must be high if current is kept low.

Large transformers are used to run transmission lines at high voltages in order to keep losses to a minimum.

But high voltage is dangerous, particularly to life, so bringing it into a house would not be an acceptable risk.

AC power is then easily and efficiently transformed to a relatively safe voltage at local transformers near the place of use.
This is not nearly as easy or cheap to do with DC.

Other reasons are:

  • DC is more lethal than AC for the same voltage because it's harder to let go of if touched as the voltage does not go through zero. (Muscles contract with constant force with DC).
  • Electrolytic corrosion is more problematic with DC.
  • DC arcs do not "quench" as easily (because voltage does not go through zero).
  • AC induction motors are simple to make and maintain. DC motors require a commutator and brushes, or complicated electronic switching.