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# How do i calculate the total resistance in a series-parallel circuit?

Discuss How do i calculate the total resistance in a series-parallel circuit? in the Electrical Engineering Chat area at ElectriciansForums.net

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#### ChalleT

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Hey, I'm an electrical engineer in training and i was wondering how you could calculate the total resistance in a series-parallel circuit? I attached a picture of what it looks like. If it's to any help resistor 1 is 2, r2 is 3, r3 is 4, r4 is 5 and r5 is 6 Ohm. Thanks for any help

TL;DR
Need help with calculating total resistance in a series-paralell circuit

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#### Loki

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Hi,

Show us your workings & we'll point you in the right direction if needed.

#### Lucien Nunes

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Hint: I would begin by transforming one mesh into a star, after which it is trivially simple.

#### PEG

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Or we could ask,how many single or groups are series,and how many are parallel?

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#### Ollienagiel

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You need to use Ohms law triangle. And also R1+R2 calculations.
Ohms law triangle -
Voltage = I(current in amps) x R(ohms)
So if you re-arrange the formulae and make R the subject. R=V/I to give you the resistors total. On resistors in series the voltage is the same and resistors in parallel the voltage drops But you need a lot more working outs or somewhere to start as it’s blank except for R1 etc

#### marconi

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This is a problem which requires knowledge of Kirchoff's Laws and simultaneous equations.

Have you covered these in your course or earlier at school?

If you have then you can use LN's hint at #3.

Or you can do a Thevenin or Norton analysis considering the bridge resistor as the load. This is actually a quicker way but for the stage of your course I reckon your are expected to use KLs and SEs.

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#### Lucien Nunes

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I'm not sure if this is what you are hinting at but I used a simple, standard transform without any need for a general algebraic solution. I did the calculation mentally as vulgar fractions. My first denominator was 11...

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#### ChalleT

I solved it by making r1 r2 and r3 to a wye-delta transformation which made it easier.

#### Lucien Nunes

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That was what I was hinting at. I chose different resistors. 3.5 ohms or so IIRC.

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#### Julie.

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Hint: I would begin by transforming one mesh into a star, after which it is trivially simple.
This

Delta star one side, then normal series parallel stuff.

It depends on what level you are looking at, if it's a first degree, I would expect you to solve one side by deriving the equations, then you would end up with either 3 with 3 unknowns, or 5 with 5 unknowns, then solve by substitution.

If not, I would expect you to be given the delta star transform and star delta, and just use whichever you choose - you can do it with either!

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