# Thread: Series circuit or parallel

1. [QUOTE=Strathead;1960724]
Originally Posted by Dennis Alwon

No, that isn't what I am saying. I am saying that any answer to your question has to make at least one assumption. Or, it isn't a complete question. It is only a circuit in series or parallel with an unknown parameter that you failed to define.

Give me a parameter that is missing, if you would-- the type of load?

2. Originally Posted by Strathead
I'll bite. This question is incomplete. It doesn't off enough information.
To some extent incomplete.

Originally Posted by Dennis Alwon
If I have a single circuit that feeds one load is that a parallel circuit or a series circuit?
Had he specified one source, one load, plus minimal necessary conductors to make it function- there is nothing in parallel and the entire circuit is a continuous series loop.

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In the physical world, it is parallel. At the application level, it can usually be treated as series.

In the physical world, there is no such thing as a point load. Even a wire is a "load" in the since current flows and voltage drops. And the wire is not a line, but a cross section. Current flows through the wire along multiple parallel paths. That said, at the level of most of our applications (a wire with a real load...pun intended), we read the overall resistance between two points....at the measurement/application level it doesn't matter that the electrons flowed along parallel paths....all we care about is the resistance between the points. And at our application level, we treat this as a series resistance.

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181129-2411 EST

Whenever any of us do any circuit analysis we make assumptions as to what the equivalent circuit is that we want to analyze.

We may assume a main panel is a perfect (ideal) voltage source, no internal impedance.

Or we may assign an internal impedancre based on a prior knowledge or some present measurements. But in neither case is it the real world. Never will be. The real world is too complex. But for most intended purposes we can make pretty good approximations.

We can also move our equivalent voltage source back to the pole transformer. Now we clearly have added some impedance. We can assume this to be series, or some combination of series and parallel.

I can choose to put my voltage source directly at my load and assume zero internal impedance. This is what Dennis did in post #1. And he created a series circuit.

We define the equivalent circuit that we think will best describe our real world circuit and be solvable.

.

.

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[QUOTE=Dennis Alwon;1960727]
Originally Posted by Strathead

Give me a parameter that is missing, if you would-- the type of load?
...parallel or series with the wires.
...parallel or series with the circuit breaker.
...parallel or series with the utility service.
etc. As I said, If I asked you right here, how far away is San Francisco, you can give an answer, but it will not be the only answer. Unless I tell you exactly where to start at, you can't give a sure answer. Parallel or series, is a relationship question. It requires a reference entity. The load is series to the wires, series to the breaker, but parallel to other loads from the panel, parallel from other panel on the same service, etc.

6. =Strathead

...parallel or series with the wires.
...parallel or series with the circuit breaker.
...parallel or series with the utility service.
etc. As I said, If I asked you right here, how far away is San Francisco, you can give an answer, but it will not be the only answer. Unless I tell you exactly where to start at, you can't give a sure answer. Parallel or series, is a relationship question. It requires a reference entity. The load is series to the wires, series to the breaker, but parallel to other loads from the panel, parallel from other panel on the same service, etc.
Still agreeing with you in that details matter. I been saying one source one load - you have nothing but series, but one can break even that down further and say that if the source is a battery it may have multiple cells in series or parallel configuration, though you may look at it as one source.
Last edited by Dennis Alwon; 11-30-18 at 01:20 PM.

7. Dennis,

is this rabbit trail these guys are off on(a wire itself is parallel) what you were considering to think it may be parallel? or just the fact about transformers and power plant also being in play?

if its that there are multiple transformers upstream, each section between isolation transformers is a seperate circuit, only magnetically coupled to the other circuits. even if you count the wire as a resistor, factor in reactance, capacitance, if you only have one (primary)load, it's series.

8. Originally Posted by Wire-Smith
Dennis,

is this rabbit trail these guys are off on(a wire itself is parallel) what you were considering to think it may be parallel? or just the fact about transformers and power plant also being in play?

if its that there are multiple transformers upstream, each section between isolation transformers is a seperate circuit, only magnetically coupled to the other circuits. even if you count the wire as a resistor, factor in reactance, capacitance, if you only have one (primary)load, it's series.

I was not intended for power plant etc being in the picture. Just the branch circuit with one load

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This is why I say that series and parallel are best used to describe portions of circuits, and that you have to say which portions you a talking about.

With respect to the wire, the different portions of the cross section are all in parallel with each other; but very few people would use 'parallel' to talk about a single piece of wire. So if you just say 'parallel' to describe a wire without specifying that you are talking about different pieces of the wire then people will look at you funny

Talking about a single source and single load (say a battery and a bulb) then the source and load are clearly 'in series'. But usually 'series' and 'parallel' would be used to describe what happens with a source and multiple loads, or multiple sources supplying a load.

-Jon

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As I noted in my original post, there is "physics" and there is "application". For the purpose of EXECUTION, we focus on application. But the essence of this thread is both. As an engineer, I sit in the middle, attempting to bridge the gap between physics and application. Both in terms of creating (engineering) things, a well as simply tying to UNDERSTAND applications and executions I know nothing about, by extrapolating back to engineering and ultimately physics.

We have MODELS that describe how current flows along paths....we have series models...and parallel models. And we have the semantics of "series" and "parallel", along with the assumptions of our model. At the APPLICATION level, we treat the wire as a single path...because our objective is execution at the application level.

Let's examine a few examples. The proverbial 25 ohm ground path. For many systems analyses, a 25 ohm linear one dimensional resistance is all we need....we get the correct answer. For other types of analysis...such as voltage gradients, the resistance becomes non-linear and multi-dimensional. The former...series is fine. The latter, parallel. It would be absurd to crunch the parallel equations for the former when all we need is the series value....considering the answer is the SAME!!! It would be likewise absurd to use series assumptions when dealing with three dimensional (or two dimensional simplifications thereof) voltage gradients.

Another example...which direction does current flow? Well, electrons flow negative to positive. But traditional current was DEFINED by the flow of positive charges..which flow positive to negative. But positive charges...are they actually flowing? Or is it just the positive "holes" we see due to the flowing negative charges. Now we're back to semantics...what does "flow" mean. What does "series" mean? What does "parallel" mean? What is physically happening?

It's good to understand these things at the physics level. Because sometimes, that understanding helps us discover issues at the application level. It is good to understand the physics path of electrons (or the reverse propagation of holes) is parallel...at the physics level. It's also good to understand when we can dismiss this level of physics and treat the process as a series...use series models....because at our application level that is all we need.

There is no right or wrong answer here when it comes to the root question. It depends on our assumptions. It depends on the depth to which we wish to analyze the question. How deep into the physics? How abstract into application? Tell me how far you wish to go....tell me your assumptions....it is only when we sit at the same level that a single answer emerges.

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