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

When it comes to confusing terms of the trade, series circuits are definitely among them. Many commercial electricians and wiremen misunderstand this term and how it works. In today’s episode of Electrician U, Dustin gives us an explanation on how series circuits work.

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Let us break everything down into their individual components and give some explanation for each and then at the end we will pull it all together and test to see if it works! It is also helpful to understand WHAT a series circuit is. Try to think of it like this- power leaves source, goes through several resistances that are IN LINE with each other, and returns to source. If you have to travel through one resistance to get to the next, that is a series circuit.
First is voltage. Kirchhoff’s voltage law states that in a series circuit, voltage is dropped across each resistance, and that the total voltage dropped is equal to the source voltage. Kirchhoff’s law also states that in a series circuit, the amperage is constant throughout the circuit. So, you will be using the same amperage rating for each calculation portion of the circuit. Resistance is pretty easy- the total resistance in a series circuit is simply the sum of them all! Rt=R1+R2+Rn. Lastly for power (wattage), the formula to be used there is P+=IsquaredxRtotal.
So now let’s see if it works! Let’s give our values for our circuit- 50v power source, 2 resistive loads at 2ohms (R1) and 4 ohms (R2) respectively, and we are pulling 8.3 amps when we clamp our amp meter to it. So, for R1 using Ohms law (E=IxR1) 8.3 x 2= 16.6v. For R2 using Ohms law 8.3 x 4= 33.3v. If we add those together, we get 50v which is our source voltage! For the amperage portion again we look to Ohms law (I=E/R) to solve. 50v/6 ohms of resistance = 8.3. So, the amperage portion is in line also! The resistance portion is pretty easy to prove in that R1 (2ohms) + R2 (4ohms) = Rt (6ohms). And lastly the power (wattage) portion. P1= E1xI (16.6v x 8.3a) = 138.9watts. P2= E2xI (33.3v x 8.3a) = 277.8watts. Added together (138.9w + 277.8w) it equals 416.7 watts worth. Now wattage can be seen as light energy (a light bulb for example) or heat energy (a toaster or space heater).
We can see by the above numerical examples that Kirchhoff’s laws concerning Series Circuits are in fact correct! Now, some of the laws WILL change a bit when we discuss Parallel Circuits and Combination Circuits and that is due to the circuit composition on how they interact with each other. Remember, for a series circuit, you must travel THROUGH one load to get to the next load. In a parallel circuit, you are hitting several loads all at the same time, and a combination circuit has elements of both.
We hope this has been an insightful look into the topic of series circuits. Is there a topic you would like to see discussed on Electrician U? Leave us a comment in the comments section and let us know. Please continue to follow Dustin and Electrician U as we are constantly adding new content to assist our followers in becoming the best electricians that they can be.

[stevesargent]

That was a great video! I'm trying to get a soon to be graduating high school senior that I know to get into the electrical trade or another. These elementary formulas are important and essential to beginners and us old timers as well. Thanks for keeping us on track!

[jeremyk]

Thanks Dustin, we just did series, parallel, series + parallel in my pre-app course. Great stuff and thanks.

[youdontknowme]

Series circuits: when one light goes out, _THEY ALL GO OUT!!!_

[crispinmacfarlane]

You're the best channel and source of electrical information out there, brother. I plan on being a master one day so I appreciate every piece of information. Love the merch too, I hope to see some EU tool belts some day.

[johnburgess]

Thanks for the fun video. I'm looking forward to when you get in to capacitance and inductance.

[nkozma]

A video on pool bonding would be great

[tedlahm]

A little much for early loaners. Either E or V is/can be used for voltage.

A or I is/can be used for current. This causes early loaners some confusion? Thank you.

[deang]

The current in a series circuit is NOT constant. It can change with thermal effects and inrush current.

What you actually mean is that in a circuit comprising only series connected loads the current is the same all the way around. That is, current isn't lost from that circuit unless you introduce a node. And then the currents can be analysed at that node using Kirchoffs Current Law.

[deang]

Wrong.
Kirchoff's current law is not about the current being constant, it is to do with the currents entering and exiting a node.

It says that the sum of the currents entering the node (or junction) is equal to the sum of currents exiting.

That is I1 + I2 + I3 +... =0


So what you do then is ascribe a direction to each current. Currents going in have a positive sign, currents coming out of the node have a negative sign. (You can even do it the other way around but it's more natural to assign positive values to currents going in).

So another way of stating Kirchoffs Current Law is: the sum of currents into a node are equal and opposite to the sum of the currents exiting a node.

[mickytarwa]

Thank you very much, educative.
Please sir, my neutral is disconnected, but there is still supply present. But it's getting high and low like crazy. With the neutral, lts low

[Afellarcouldprobablyfixit]

Any plans to offer certified ELO’s in Washington state?

[lighthumor]

Large scale constant current circuits exist as well - the two main applications being airfield lighting and street lighting. They're most often 6.6A but they can be 20A as well. I own a company (OV20 Systems) that supplies the series street lighting market. Most electricians don't realize series street lighting still exists. I geek out on this stuff all day so if anyone knows of any series street lighting, or if you have questions, feel free to reach out!

[rogerpenske]

Can these formulas be used to determine which light in a string of Christmas lights that are wired in series, is the one bulb that is no good?

[mustafamalik]

Hello Dustin, I just found your channel recently, great content and was wondering if your videos cover codes in the Canadian electrical code. If it does not do you know a YouTuber that specifically explains Canadian electrical code for apprentices?

[lorenzojohnson]

You wrote 13.3 instead of 33.3 in your P2 formula

[noferblatz]

So... you're getting the same amperage through each component? So regardless of whether the resistor is 2 ohms or 4 ohms, the amperage (number of electrons through the component per second) is the same? This sounds counter intuitive.

[bryanduchane]

Understand the principles of "Series Rules" you talked about. Is this the reason a Series Rated panel can have lower AIC ratings in the branch breakers as long as the main breaker is rated for the specified AIC rating??
Never understood why some Engineers will not allow panels that are series rated.

[garymiller]

I'm an electrical contractor in state of Florida had my Florida electrical contractors license for 40 years continuing education every two years I had all Electrical formulas that pounded into my brain where I could do it in my sleep, I like going from 3 phase I going to Delta 3 wye phase efficiency factor Do that my sleep too

[edwardhuster]

Lights in old school were wired in series. When one burned the resistance is infinite. So all lights go out.

[waynegram]

DUSTIN, it would have been nice if you would have shown the formulas of converting wattage into dissipation of light and heat and stored joules because its different formulas. Voltage multiplied by current = wattage power ( not dissipation of heat, light or stored joules ) When a capacitor is storing current you can't use this formula V*I = stored voltage/stored current, for lamps dissipating light you can't use this formula V*I = lamps dissipating light, for resistors dissipating heat you can't use this formula V*I= for resistors dissipation heat. Batteries are dissipating chemical converting it to a DRAIN current but you can't use the formula V*I = The Battery dissipating drain energy. Try to make another video showing the correct formulas to convert power wattage into heat, light, stored joules.