Electricity Explained

Getting Down To Basics

By Bruce W. Maki

Electrical Devices:

Switches, Lamps, Heating Elements and Motors

Electrical Heating

The most basic electrical devices in the home are actually made from simple pieces of wire. There are special metals that have extra resistance, much more than the wires in the house, and when household voltage is applied (typically 110 to 120 Volts) these pieces of metal will heat up.

This is the principle behind electrical heating, also called resistance heating.

Suppose a short piece of special wire has a resistance of 12 Ohms. When 120 Volts is applied, there will be current flow of 10 Amps. (120/12=10)

The wire will become warm, maybe even red hot. Since the supply wires in your house are designed to have very low resistance, they don’t become warm with 10 Amps flowing through them.

This principle of resistance by design is found throughout all homes. Electric ranges, ovens, toasters, space heaters, water heaters, coffee makers, and incandescent light bulbs all employ special metals with higher than normal resistance to create heat where it is wanted.

As mentioned before, switches are used to break a circuit and stop the flow of current. When a switch is in the ON position, the metal components form a complete path and electric current flows. The switch is said to be ‘closed’.

When the switch is move to the off position, the metal components are separated, stopping the flow of current. The switch is said to be ‘open’, and the circuit is ‘incomplete’.

The other major electrical device found in the home is the motor. Motors are fairly complicated. Basically, a motor uses a moving magnetic field to force a magnet to rotate.

The rotating magnet can be mechanically connected to a fan, as in a hair dryer or vacuum cleaner or air circulating system; or a pump, as in a refrigerator, dishwasher, well, or clothes washer, or many other mechanisms.

For the purposes of most household repairs, a motor is technically simple: apply voltage, the motor turns; remove voltage, the motor stops.

Controlling motors is almost always done with simple, ordinary switches.

Larger residential grade motors, such as a furnace blower motor, use a capacitor to help them start. Often a non-functioning motor of this type can be repaired by replacing the starter capacitor, which costs a lot less than replacing an entire motor.

Large commercial and industrial motors do get quite complicated, primarily in the elaborate methods used to start them.