Let's Talk About COMBINATION Circuits: Voltage, Current, Resistance, and Power

We have talked about series and parallel circuits. But have you ever wondered how a series circuit works or what it even is? In today’s episode of Electrician U, Dustin covers part 3 of our topic on circuits- Combination Circuits!

00:00 - Intro
00:13 - Combination Circuits
02:17 - Voltage
11:00 - Power

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A combination circuit is simply a circuit that has properties of both series circuits and parallel circuits within it. And, remembering that trying to figure out values for Voltage, Amperage, Resistance, and Power each require different formulas depending on what type of circuit it is. So, the easiest way to calculate values for these in a Combination Circuit is to simply start adding all the groupings of parallel circuits resistances together (this will need to be done a few times depending on how many there are) until we are left with a simple series circuit!
Let’s review the rules. Voltage- in a series circuit voltage is dropped across each resistance while in a parallel circuit it’s constant. Current- in a series circuit current is constant but is proportional to the resistance in a parallel circuit. Resistance- in a series circuit resistance is the sum of all the resistances while in a parallel circuit it is the inverse. The formula for wattage in a series circuit Pt=I squared x Rt and in a parallel circuit its P=E squared/Rt.
Let’s do one. Say we have a 100v power source and a combination circuit of 7 loads with the following resistances- R1-1, R2-2, R3-3, R4-4, R5-4, R6-3, R7-2. R6 & R7 are in parallel with each other, R4 & R5 are in parallel with each other, and those 4 are in parallel with R3. We will add R4 & R5, R6 & R7, and then add those together and then add it to R3. Since each set has only 2 resistances, we can use the product over sum method. Adding R4 & R5 we wind up with 1.7 ohms. Adding R6 & R7 we end up with 1.2 ohms and adding those together we have 2.9 ohms. Now we can add R3 and R4567 and have an end result of 1.18 ohms! Now we have 3 loads in series with one another and can complete our calculations!
The total resistance of our circuit is the sum of all the resistances- 1 + 1.18 + 3= 5.18 ohms. The total amperage of our circuit is the voltage divided by the total resistance- 100/5.18 ohms or 19.3 amps. Voltage is dropped across each load and is equal to the source voltage. The formula is amperage multiplied by the resistance = voltage. R1- 19.3 x 1= 19.3v. R2- 19.3 x 1.18= 22.8v. R3- 19.3 x 3= 57.9v. Add those together and we have 100v or our source voltage! Lastly, we have the power to work out. Amperage x the voltage of each load = the power consumption of each and we would add those 3 values to get our total circuit power. P1- 19.3 x 19.3= 372.5w. P2- 19.3 x 22.8= 440w. P3- 19.3 x 57.9= 1117.5w. And our total power for the entire circuit is the additive of these. 372.5w+440w+1117.5W=1930w.

[stevesargent]

Keep up the Ohms Law info! Essential to learning the basics!

[yankluf]

That you call “craziness” to that simple parallel circuit makes me feel SO, SO UNDERSTOOD 😂😂😂 Thank you so much!!!!

[laganas]

Thank you so much. I'm not actually studying to become an electrician but I've always loved maths and I've recently become interested in electrics having recently moved into my own house. Videos like these are great. New subscriber.

[EnProto]

Timing this video right around when 1st year apes are going through DC combo circuits is a good move!

[mikepeters]

Well done. For us electricians it’s a nice refresher but if you’re trying to teach new would be apprentices, maybe slow down a little. Maybe explain that the current that’s flowing is coming from the supply so it doesn’t sound like it’s just magically appearing, and after you sum up the resistances, then you can break them down again to see the current that flows in each branch of the circuit. And further to the power dissipated by each resistor in each parallel branch.
You scratched the surface nicely, but there’s a lot more to it.

[munecawilliams]

I was stuck on a problem and you helped tremendously. Thank you❤🎉

[ghtxbarbers]

Your video are very clear and explained well I just clicked that subscribe button! Thanks for sharing.

[mr.c]

Dustin, I understood v. drop in a better way. Thanks 🇺🇲

[scroopynooperz]

This is essential info for the prepper - everything is going to sh!t pretty quick now and it's important to know you can do some basic maintenance and repair when the time comes.

Thanks for the upload.

[jorgecampos]

Thak you so much dude, you are the man. 😁😁

[Sembazuru]

Flash back of my basic electronics course. Next step, evaluate a Wheatstone Bridge. Well, for electronics that is a next step to learn how to use a Wheatstone Bridge to make a simple resistance meter and then see how to apply that for various sensors that use a variable resistance for the sensing element (strain gauges, temperature sensor, etc). Are Wheatstone Bridges used much in electrician work?

[michaelyarbrough]

I just wanna say I have been watching you a long time I’m getting ready to take my journeyman’s test I’m from temple Texas I found your videos and I thought it was cool that you were in Austin, anyway can you do a video about code I seen your video about exam preparation but could you do more in depth about code

[hoffmanfiles]

You should do a video on what a parallel circuit is like do you mean a house circuit or a motor circuit. And you should do a video on what a series circuit means do you mean house. I think you should do videos that relate to the actual job. It will help us actually visualize and relate the class like preaching and Choctaw to actual on the job skills.

[BlackHoleForge]

As the bell strikes midnight, another video is released. Hopefully I'm not too tired to understand it. Hey, but we always have tomorrow.

[marie-francemayer]

I know that video has been up for a little while but would it be possible to address re expanding your circuit to find voltage and current through each resistor including the ones in parallel

[ikeraiser]

op is it possible to use a gfci outlet in a dc to ac inverter device without the need for a gfci breaker?

[austinduty]

Hey Dustin, you’re in MA now, are you gonna offer a continuing ed or a 6 hour for MA electricians?

[jgleigh]

If you're just looking for power through the loads, it'd be easier to just use (current-squared times resistance). No need to solve for voltage drop first.

[ice]

I have been so confused doing homework for this I got series and parallel separately I just can’t grasp how to combine them

[troybrown]

Can you do video on ARMS (Arc Reduction Maintenance System) Circuit breakers above 1200A?