The Advantages & Disadvantages of Series and Parallel Circuits

Updated March 23, 2017

Electrical circuits deliver electrical power from a source to a device that uses it, such as a light bulb or a speaker. Some common components of circuits are power supplies, resistors and switches. Each component has a particular job and each component does its job differently depending on whether it is wired in series or in parallel within the circuit. Wiring components in series means they are arranged along one stretch of continuous wire, whereas parallel wiring means that the wiring forks and the components are placed side-by-side on parallel sections of wire.

Power Supplies (Batteries) in Series versus Parallel

Power supplies in circuits, which are often batteries, create a voltage difference across the circuit that drives electrical current. The greater the voltage difference, the greater the current. Batteries can supply that voltage for only a limited time. Wiring batteries in series with one another within a circuit increases the total voltage applied across the circuit. For instance, three 5-volt batteries wired in series with one another will create a total of 15 volts. The current within the circuit will increase proportionately. Batteries wired in parallel do not add their voltages together, but their capacities are added up. This means that if one 5-volt battery would normally power a circuit for two hours, two 5-volt batteries wired in parallel might power the circuit for four hours, but still supplying only 5 volts to the circuit.

Resistors in Series versus Parallel

Resistors damp or slow the current that a circuit delivers to the device using the electrical power. This is useful when a power supply can deliver more current than is necessary to the device using it. Resistance is measured in units called Ohms. Much like power supplies, resistors that are wired in series yield added overall resistance. Three 2-Ohm resistors wired in series would yield a total of 6 Ohms of resistance across the circuit. Resistors wired in parallel yield an inversely additive total resistance, which is usually less than the smallest resistor. The total resistance of three 2-Ohm resistors wired in parallel can be expressed as:

Total Resistance = 1 / (1/2 + 1/2 + 1/2) = 0.67 Ohm

Switches in Series versus Parallel

Switches control whether current flows through a circuit or not. Closed switches allow current to flow, whereas open switches break the circuit and stop the flow. When switches are wired in series, only one switch needs to be open to stop the flow of current. This can be useful when you have a long circuit and want to be able to turn it off and on from different places, such as when multiple light switches control the light in the centre of the room. When switches are wired in parallel, they all have to be open to completely stop the flow of current to the whole circuit, but different combinations of opened and closed parallel circuits can redirect current to different components--such as resistors, powered devices and power supplies--within the circuit.

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About the Author

Timothy Banas has a master's degree in biophysics and was a high school science teacher in Chicago for seven years. He has since been working as a trading systems analyst, standardized test item developer, and freelance writer. As a freelancer, he has written articles on everything from personal finances to computer technology.