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Bryan talks about parallel circuit resistance. He discusses what happens when you take multiple electrical circuits and run them in parallel. When you run equipment in parallel, a separate path goes to each load.
The load is the part of an electrical circuit that does something. Examples include motor windings (inductive) and filaments in lightbulbs (resistive). When you run multiple loads in parallel with each other, you connect each side to the power supply.
In a series circuit, the loads are connected to each other, not each to the power supply. The electrons must move through each load as they proceed to the final load. You can add up the resistances of each load to get your total circuit resistance.
In a parallel circuit, the voltage is the same across all the loads. That’s why you can get 120v to the lightbulb in your bathroom and in your bedroom all the way across the house. For amperage, you add the amperage of each circuit to get the total circuit amperage. However, the resistance DECREASES for each load you add to the parallel circuit.
If you connect a single lightbulb to a circuit, the total circuit resistance is just that of the bulb (and an insignificant amount from the conductors). When you add another bulb to the circuit, the resistance decreases; you can calculate the total circuit resistance by dividing each load’s resistance (R) into 1 (1/R). Then, you add those values together to get total resistance (Rt) and divide that sum into 1 (1/Rt).
The idea is to get you to understand the relationship between resistance, voltage, and amperage in a parallel circuit. You have more current in a parallel circuit, so you will have lower resistance. The more parallel circuits you add, the more current you will draw; in turn, your total circuit resistance will be lower.
In a parallel circuit, electricity does NOT take the path of least resistance; it takes all available paths. The amount of current is just proportional to the resistance.
You can read our HVAC School article on Parallel Circuit Resistance at
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Hey thanks for watching this video we're going to talk real quickly about parallel circuit resistance. What happens when you take multiple electrical circuits and you run them in parallel with each other, meaning that there's a separate path that goes through each load? When you hear load, some people may not know what that means, but basically a load is the part of an electrical circuit. That does something, so it would be like the windings in a motor or the filament in a light bulb or the coil on a stove or in an oven. So the part that actually creates light heat magnetism.

That is your load and when you run more than one load where they are in parallel with each other, meaning that you're not going in and out of one to the other, like you do in a series circuit, but but you're, connecting each side to the power Supply it affects the resistance of that circuit differently. So let's talk about how that works. So, first off in a series circuit, the loads are connected in a row or end to end and it's you know. We see this in christmas lights uh when you have christmas light bulbs and one goes out the old school christmas lights, then they all go out and that's because the electrons have to actually move through each load and they're very simple.

All you do is, you just add up the resistances, and then that is your total circuit resistance, but in a parallel circuit the voltage is the same across all the loads, so each load gets the same voltage. So, for example, that's why every light in your house has 120 volts because they're all wired in parallel with every other light, the amperage in a parallel circuit is simply added up, so you just take the amperage of each circuit. You add it up. That's the total amperage of whatever you're measuring, but the resistance is a bit more tricky.

It gets tricky to imagine because the total circuit resistance of parallel loads goes down the more loads that you add. For example, if you have one light bulb connected to a power source, the total resistance of the circuit is just the resistance of the bulb, so one bulb circuit resistance is just the resistance of the bulb, and maybe whatever is in the conductors, which is going to Be next to nothing, if you add another bulb in parallel, the resistance of the circuit actually goes down. So if you're, considering you know two bulbs in parallel, it's in one circuit but they're both connected to the power supply. Then the resistance of that total circuit goes down.

So here's how you do that to calculate the resistance of a parallel circuit. You take each individual resistance of each load, each circuit within the parallel circuit that you're measuring and you divide it into not by one. So you divide it into one, so that would be one divided by resistance, not resistance, divided by one. When you do the calculations, you then add up all the resistances that were divided into one and divide the sum into one.

So the formula is going to look something like this. So if you look at this particular illustration that we have here, one divided by rt, which is total resistance, equals 1 divided by 120 plus 1 divided by 45 plus 1 divided by 360.. So, at the end, our total resistance is going to be 0.0331. That's how we do the math at the end.

It's not often that you're going to do this, but the main thing that i want you to think about in terms of ohm's law in terms of watts law is that when we have lower resistance, we have more current lower resistance equals more current. So it stands to reason that if you have multiple parallel circuits and you add up those currents and that equals the total well, then you're going to actually have lower total resistance. The more parallel circuits, you add, the more paths that you give the electrons to flow through the more current you're going to have a lot of people will say: well, electricity takes the path of least resistance. If that were the case, if electricity only took the path of least resistance and not the other paths, then the only circuit on this diagram that would have any current whatsoever would be the 45 ohm circuit, because it's the lowest one, but we see that it actually Takes all paths and the amount of current that flows through each path is proportional to its resistance and the more parallel circuits you have the lower the total circuit resistance, so the lower the resistance, the higher the amps, adding in additional parallel loads increases the amperage in A circuit we see this every day when we notice that compressor, amps and condenser fan amps added together equals total condenser amps.

So that means that those two loads together actually have lower resistance than either of them individually. That can sound counter-intuitive because of how we think about what resistance is, but the reality is. Is that the more current you have the lower circuit resistance you have so that's it. Electricity takes all of the parallel paths and the more parallel paths you have the lower.

The total circuit resistance and again, if you want to know how to do the math, we actually have a article on this hvcr school dot com, slash parallel dash circuit dash resistance. So that's what this video is coming from if you're in school. Hopefully, you found this helpful in the field you're not going to run into this a lot, but just understanding that resistance goes down with more loads can be something that will make things make sense when you're using your own meter a little a little bit in the Field thanks for watching our video, if you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click, the notifications bell to be notified when new videos come out, hvac school is Far more than a youtube channel, you can find out more by going to, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more. You can also subscribe to the podcast on any podcast app of your choosing.

You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching you.

12 thoughts on “Resistance in parallel circuits”
  1. Avataaar/Circle Created with python_avatars meabob says:

    In the 11th grade (43 years ago), I got in an argument with our electronics teacher when we got into parallel circuits. He had been telling us that electrons take the path of the least resistance. When questioned, he explained how the electrons will follow all paths available. I asked him why were we told the least resistance path narrative if it was not true. He said because he was the teacher and he teaches how he wants. I told him that teaching lies makes him a liar. I got sent to the office. The next year, he wasn't there anymore.

  2. Avataaar/Circle Created with python_avatars Brandon Conley says:

    Thank u Service area Ottawa??

  3. Avataaar/Circle Created with python_avatars jamesmofo62 says:

    Do you have any video to prep for core Nate test?

  4. Avataaar/Circle Created with python_avatars Laurence bernabe Meñoto says:

    Hi! i am interested in everything. Can i enroll out of the country. Very inspiring teaching easy to learn and understand. I hope i can enroll to learn more.

  5. Avataaar/Circle Created with python_avatars Mitchell Armyguy says:

    (120^(−1)+45^(−1)+360^(−1))^(−1)=30….I find it easier using the reciprocal method…. then you can add any thing that is in series with the parallel circuit. By simply putting the addition before your first parenthesis. Such as 560+(120^(−1)+45^(−1)
    +360^(−1))^(−1)=590… if you have a good calculator it easy to plug this in but it's very doable even on your phone calculator

  6. Avataaar/Circle Created with python_avatars Trust_Jesus1213 says:

    Yayyy!! I'm the 100th 👍…. thats better than 1st forsure

  7. Avataaar/Circle Created with python_avatars Chris Durham says:

    Great video!!
    Load = work

  8. Avataaar/Circle Created with python_avatars Peter Smith says:

    How do yall feel about uv lights?

  9. Avataaar/Circle Created with python_avatars Robert Miller says:

    I think that this might be better explained if we point out that these examples are for pure resistive loads only. Motors or inductive loads, act differently. The terms are different. The term used is circuit impedance in AC circuits. And the load of each motor, transformer, contactor coil, compressor motor etc. is a result of the "reactance" of that device. In fact, the reactance will be different for 50 Hz than it is for 60 Hz. Don't go using an ohmmeter on motors to get a winding resistance and then selecting fuses and wiring. It just will not work.

  10. Avataaar/Circle Created with python_avatars Manzoor yatoo Yatoo says:


  11. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:

    All learning nuggets!
    Stay safe.
    Retired (werk'n)keyboard super tech. Wear your safety glasses.

  12. Avataaar/Circle Created with python_avatars Arthur Grant says:

    Always doing a great job in teaching others! Never stop, love your dedication towards a better service industry! Thank you Bryan Are you in Kanata ?

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