Household circuits
1. Why are there different circuits for lighting, heating and other appliances in a house?
When a current passes through a conductor, heat is generated. The amount of heat
generated increases as the current through the conductor increases. Each piece of household
wiring is designed to carry a certain maximum current without overheating. However,
different devices have different power requirements and have different current requirements
because voltage is the same in all domestic supplies. So, for example, the circuit connecting
devices requiring high currents (e.g. ovens and hot-water systems), it would be necessary to
use wider-gauge wiring to avoid overheating and circuit breakers that are designed for the
high current. Thus, different circuits are needed for lighting, heating and other appliances
because the current requirement is different for each one.
2. Compare the structure of a household circuit for different purposes.
In general, there are a number of circuits each designed to carry a certain maximum
current, each with a fuse in the active wire. There are separate circuits for light outlets, power
outlets, the stove and the hot-water system. The outlets in each circuit are connected in
parallel, so that each appliance will have 240 V across it. There is a switch in series with each
outlet, enabling each appliance to be switched on and off independently of the other
appliances; this switch is on the active side of the appliance because if the switch were on the
neutral side, the appliance could cause an electric shock even if it were switched off.
Furthermore, some domestic appliances, such as pottery kilns and large air
conditioners, use three-phase alternating current. Three-phase AC is supplied using three
active wires, each one-third of a cycle out of phase with the other two, and one neutral wire. It
can supply a more consistent power to a device because current continues to be supplied to
the other two phases when the third is zero, resulting in a more consistent flow of current and
a corresponding increase in power to the device.