In a series circuit, components are connected like links in a chain. If any link fails, current to all the components is cut off.
In a parallel circuit, all components are connected directly to the voltage supply. If any connection or component fails in a parallel circuit, current continues to flow through the rest.
This is one reason why parallel circuits are used in automotive applications like lighting systems. If one lamp fails, current continues to flow through the rest. In a series circuit, all would go out, which could be disastrous.
Also, since all components connect directly to the battery terminals, the metal of the vehicle’s body can become one of the conductors. One terminal of the battery, and one of each component, can be connected anywhere on the body or chassis, to complete the circuit. This is called an earth, or ground connection. It saves a lot of connecting wire.
A feature of a parallel circuit is that the voltage across each component is the same as battery voltage.
No matter how many components are added, or removed, as long as they’re in parallel, the voltage across them will be the same as across each other component, including the battery.
Another feature of a parallel circuit is that the current flowing in each branch is determined by the resistance of that branch.
In a parallel circuit where the resistors in each branch are the same, the current flowing in each branch is therefore also the same. However, the sum of their individual currents is equal to the total current flowing in the circuit.
When the resistance's are not equal, then the current divides in accordance with the value of each resistance, but the total current flow is still the sum of the currents flowing in each branch.
