Parallel Circuits

Parallel Circuits

Parallel circuits are probably the type of circuit with which most people are familiar. Most devices such as lights and receptacles in homes and office buildings are connected in parallel. Imagine if the lights in your home were wired in series. All the lights in the home would have to be turned on in order for any light to operate, and, if one were to burn out, all the lights would go out. The same is true for receptacles. If receptacles were connected in series, some device would have to be connected into each receptacle before power could be supplied to any other device.

Parallel Circuit Values


Parallel circuits are circuits that have more than one path for current flow.  One of the rules for parallel circuits states that the total current flow in the circuit is equal to the sum of the currents through all the branches. This rule is known as current adds. The amount of current leaving the source must return to the source.

Voltage Drop

A second rule for parallel circuits states that the voltage drop across any branch of a parallel circuit is the same as the applied voltage. For this reason, most electric circuits in homes are connected in parallel. Each lamp and receptacle is supplied with 120 volts.

Total Resistance

The total resistance of a parallel circuit is always less than the resistance of the lowest value resistor, or branch, in the circuit. Each time another element is connected in parallel, there is less opposition to the flow of current through the entire circuit.  Imagine a water system consisting of a holding tank, a pump, and return lines to the tank. Although large return pipes have less resistance to the flow of water than small pipes, the small pipes do provide a return path to the holding tank. Each time another re- turn path is added, regardless of size, there is less overall resistance to flow and the rate of flow increases.

Finding the resistance of a parallel circuit is the reciprocal formula of a series circuit