Parallel circuits are electronics circuits that have several different paths for current to follow, like a highway or river that branches off into many smaller routes or streams and then comes back together into a single source. In a parallel circuit, current will continue to flow, even if one part of the circuit is blocked. Your household electrical wiring is a good example of how parallel circuits workif a lightbulb burns out in a lamp, it doesn't plunge half the house into darkness. When calculating the parameters of parallel electrical circuits, three measurements need to be known: voltage, amperage, and resistance.
Things You'll Need
 Calculator
 Multimeter

You can calculate the voltage of any part of the parallel circuit by knowing the voltage of the source of the circuit's power. In other words, the voltage is the same on any of the paths of a parallel circuit. Here's an example: If you have a 12volt battery connected in parallel to four light bulbs, each will draw 12 volts of power from the battery. The 12volt battery is the source of the circuit's power, and each of the light bulbs is a parallel circuit path.

Calculate the amperage of the parallel circuit by adding the amperage of all the components on the parallel paths. For example, if the four light bulbs in the example in Step 1 each draw 2 amps, the total amperage of the parallel circuit will be 8 amps.

Calculate the total resistance of the parallel circuit by using the formula 1/Rt = 1/R1 + 1/R2 + 1/R3, and so on depending on number of components, where Rt is the total resistance, R1 is the resistance of the first path, R2 the second, and so on.
References
 Electronics For Dummies; McComb and Boysen; 2005
 Understanding parallel circuits
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