multiwire circuits

[Anonymous No.16575129]

What is physically happening here? this is a multiwire branch circuit with phases 180 degrees out of phase. As i've heard it explained, the "currents cancel" when they both travel on the neutral and it only carries the net difference. But what exactly is canceling? As I understand it current isn't actually (just) the movement of electrons, so it's not like equal electrons are moving both ways. Is it like the picture suggests and you have two different waves traveling independently and it just "looks" like they cancel on the neutral? do the waves "crash" and completely stop each other from continuing flow? is it just stationary EM fields that cancel where they meet? how are you able to derive power from these currents just "cancelling".

[Anonymous No.16575158]

>>16575129
write the currents as vectors
they cancel
/thread

[Anonymous No.16575395]

>>16575129
magic

[Anonymous No.16575697]

Did the smarter EU browsers get off work yet?

[Anonymous No.16575991]

>>16575129
No, I can't tell you WHAT physically happens in the wire. But I can measure it. I can show it as the summation of two independent out of phase currents. I have a very good understanding of it and that's good enough for me. I'm not distracted by the philosophical side of WHAT happens inside the neutral wire.

[Anonymous No.16576026]

>>16575129
The electricity is just electrons wiggling back and forth. In the middle wire they don't move.

[Anonymous No.16576075]

>>16575129
Who the fuck made this retarded image? Having the bulbs like that is just going to confuse people.

[Anonymous No.16576229]

>>16575158
this
also fun fact if you have capacitor on one phase and inductor on other, current on neutral wire will be sum of phase currents.

[Anonymous No.16576362]

>>16575991
i'm not even asking philosophically. I just want the scientific explanation of what happens. If the load is balanced, you can completely cut the neutral and it changes none of the currents
in each bult. Is that just a happenstance not a general rule? With your summation, the implication is that the phase currents are ALWAYS traveling on the neutral they just cancel out. What would be the difference between that model and one where the current only flows between the top and bottom and only the imbalance on the neutral.

[Anonymous No.16576432]

>>16576229
Is there specific value/ratio inductor/capacitors I would need to use if I wanted to test this out? Does it matter if I use batteries? How does the phase current explanation work when the power is DC?

[Anonymous No.16576564]

>>16576432
in case of pseudo two phase the smaler power factor the better (you want curents +-90 deg out of phase with voltage), in case of 3 phase you want +60 deg and -60deg and you can get difference or sum of currents depending on which two phases you connect (phases are 120 deg apart). With dc Inductors start producing constant magnetic field and then become invisible to DC, capacitors start invisible and then behave as open circuit for DC. If you have +dc, 0, -dc you can only get difference between currents without more fancy electronics components. L to C ratios are for resonance to get maximum power and depends on frequency.

[Anonymous No.16576705]

>>16576564
oh, nvm I think I understand what you're saying. but this is just causing each current phase to lag voltage such that when they meet at the neutral point they're in phase right?

The question i'm trying to answer is whether both phase currents really return on the neutral. If the load is equal on top and bottom, then the two have the same magnitude with opposite signs. So what's the difference between describing it as one current vector along the top and bottom, and two current vectors that cancel along the neutral? where would these two descriptions give different results?

[Anonymous No.16576707]

>>16575129
>phases 180 degrees out of phase
Isn't it just the sinusoids canceling?
It's destructive interferance

[Anonymous No.16576726]

They are 240 volt in ohase and the current flows through one to another. The middle 'neutral' does not carry current.

You get the 120 volt by splitting the 240 with transformer having two coils at output end totaling same amount of voltage. In this you just forget the splitting and use the 240.

[Anonymous No.16576876]

>>16576705
In pseudo two phase current under such circumstances current just goes through whole length of your transformer winding, hot wires, orange part from one bulb to the other and those bulbs and nothing returns via neutral, if everything is perfectly balanced, otherwise some current goes back via neutral and closes loop on half of your winding.
>>16575129
>is it just stationary EM fields that cancel where they meet?
If you look at electric field nothing special happens at orange point. Current just goes from top to bottom and rest of orange wire (from point back to the left) has 0 V/m electric field, 0 V to the ground, 0 A of current

[Anonymous No.16576926]

>>16576726
>>16576876
i get that interpretation. I'm asking how you prove one or the other. If I responded "nope both phases travel along the neutral and cancel so you get 0 V or current", what would you use to show that's not true. In the case of a balanced load, they give the exact same answers for current along each resistor and the neutral. in the case of an imbalance, current on the neutral makes sense because the two waves don't completely cancel, they are mirrored but one has a bigger amplitude. in the view of current flowing top to bottom, you have an imbalance cause....why? if it was working in series before, why would it ever pull any more amps than equal? and why would the current split two ways?

[Anonymous No.16576934]

>>16575129
Lmao at how the EEfags here can't answer your question and repeat the same shit. They don't know what physically happens inside this circuit. They are abstracted away from it by their shitty circuit diagramms and laws applied to it.

[Anonymous No.16576935]

Lmao at how the EEfags here can't answer your question and keep repeating the same shit over and over again. They don't know what physically happens inside this circuit. They are abstracted away from it by their shitty circuit diagramms and rules applied to them.

[Anonymous No.16576940]

>>16576935
to be fair, I phrased it wrong. I don't actually care what the electrons are "really" doing. I'm asking for the differences if you model it one way vs the other, or if there even are any.

[Anonymous No.16576958]

>>16575129
The middle voltage is always 0v.
If the lightbulbs are the same, this will cut the voltage in half. The halfway point between the 2 endpoints is 0

[Anonymous No.16576989]

>>16575129

https://nationshomeinspections.com/multiwire-branch-circuit/

[Anonymous No.16577034]

>>16576989
>the two circuits are trying to push in opposite directions
Holy fucking aneurism.

[Anonymous No.16577050]

>>16576989
Are u retarded? This explains nothing about what I’m asking. You don’t think maybe I already read where it came from??

[Anonymous No.16577072]

Equivelant circuit: two 1.5batteries in series, then two lamps in series. Then extra wire from between batteries to between lamps

[Anonymous No.16577088]

>>16576362
>If the load is balanced, you can completely cut the neutral and it changes none of the currents
Cutting the neutral turns it into a 240 volt circuit with each half in series. The reason that's fine if there's a balanced load is that you double the voltage but also double the resistance. If there's a load imbalance, then that's no longer true.

[Anonymous No.16577096]

Cold Take: As someone that had to do a bunch of electrical work on a house that had more than a dozen unlabeled multi-wire branch circuits, ended up working on shared neutrals that would have been carrying load had the wrong switch been flipped, and seeing the mess of a breaker box we were left with after we found out it needed replacing filled with tied together breakers all over the fucking place, FUCK multi-wire branch circuits and anyone that uses them. From what the electricians said they aren't even that common and they made working with the system annoying as all fuck.

It's fucking horrifying to me that some idiot removing a tiny piece of plastic before the next person comes along is all it takes to potentially get someone electrocuted or a circuit fried.

You shouldn't use these just for the dropped neutral risk alone. Just run the extra god damn wire.

[Anonymous No.16577151]

>>16577088
Right, but if your theory was that they run in series when balanced, you would say cutting the neutral did nothing because they were in series before. When do the differences matter?

Does the possibility of an imbalance disprove the series circuit model? Like if the top circuit was 12A and the bottom 10A, is it reasonable to say that from the 12A, 10 go to the bottom in series and 2 to the neutral?

[Anonymous No.16577153]

>>16576926
>I'm asking how you prove one or the other.
Use Kirchhoff's laws (no charge free of charge at junctions, no free energy by dragging charge through loop)? Or do you want some explanation going from quantum field theory or what?

[Anonymous No.16577160]

>>16577151
>they were in series before
They aren't. They both connect to ground in parallel.

>Like if the top circuit was 12A and the bottom 10A, is it reasonable to say that from the 12A, 10 go to the bottom in series and 2 to the neutral?
Yes. Not only is that reasonable to assume, that's exactly how it works.

[Anonymous No.16577178]

>>16577153
No that’s fine…so using kirchoff’s and looking at each circuit individually, I get that each side will flow back on the neutral and currents cancel. Is this the correct solution or did I do something wrong?

>>16577160
You seem to be saying different things. If they weren’t in series before, then they both flow together on the neutral and cancel. But then on the line you seem to say 10A flow in series, and 2A on the neutral.

[Anonymous No.16577184]

>>16575129
Think of it like this, if top and bottom are perfectly out of phase and have the same magnitud and the lamps have the same resistancs, then the situation is symmetrical around the neutral. Therefore, every tiny amount of charge that goes into the circuit by the top wire is sucked out of the circuit it by the bottom wire. Thus no current flows in the neutral. Whats depicted in your circuit are the mesh currents which may or may not be equal to the branch current ie what actually flows through the lamps . Mesh currents are a mathematical tool branch current it's what is actually flowing through a component.

[Anonymous No.16577209]

>>16577178
>But then on the line you seem to say 10A flow in series, and 2A on the neutral
Current in=current out with any circuit configuration

[Anonymous No.16577803]

/sci/ has been garbage for at least a decade. It's 99% undergraduates that MAYBE paid attention in class. At least before if you got lucky there were a handful of actually knowledgeable people who might give a useful answer, even though they were disgusting tripfags. reddit is unironically the better place for questions i've learned.

as >>16577072 said, you draw the equivalent circuit and solve with superposition. both circuits run along the connection point of the two batteries. the "physical" explanation is wires are just a way of directing fields, and the two fields both directed along the neutral result in a zero field, by superpostion.

The series explanation makes no sense physically nor by virtue of circuit theory. You create a parallel path with zero resistance, but no current flows? or if you change a resistor creating a so called imbalance, why would JUST changing a resistor change the current path in the first place? If it's a series circuit before, it's a series circuit after and I_1 = I_2 regardless of resistor values or equivalence. that is not the case and in fact their values are are equivalent to two resistors in parallel at half voltage or equivalently, their value by solving the circuit with one battery elimnated (superpostion).

as >>16577088 said there is only an apparent equivalence in the niche case where you double the voltage and resistance. It makes no sense otherwise.
Here's a fun experiment or just something simple to model in a circuit analyzer : make it 3 batteries instead and now there's no way to connect to a midpoint. but if this is a series circuit, it shouldn't matter. make a parallel path between the lamps and between any two batteries, is there current on this path?

>>16577096
The only thing wrong with edison circuits is the retards that are expected to work on them. maybe stop randomly disconnecting wires you glorified color matcher.

[Anonymous No.16578013]

>>16577803
>maybe stop randomly disconnecting wires
Nothing was being randomly disconnected. The fucking shared neutrals were connecting through fucking outlets and the outlets needed replacing.

Not a fucking problem if you can turn off all the electricity in the house (which I couldn't due to other work going on) or if the shared neutral is clearly labeled so you know to turn off every circuit running through that fucking outlet (which none of them were), but when the power for the outlet's on switch 12 and the neutral for the outlet's on breaker 12 and 17 and nothing anywhere in the house fucking says that, that's a fucking issue. Circuit testers aren't gonna show current on the neutral unless something's *on* which doesn't fucking save you from something *turning on* while you work if you missed which god damn breaker the fucking neutral is on.

Best case scenario, a MWBC is on a double breaker with an actual single handle for both halves, but nothing's stopping the next guy along from replacing that with 2 single breakers cause it's cheaper and the guy after that from missing the MWBC and getting bit.

There's no god damn good reason to put anyone at the mercy of someone else's stupidity if you can just make shit idiotproof in the first place by running 2 wires.

[Anonymous No.16578015]

>>16578013
Also
>inb4 someone suggests just turning off all the power in any building you're working on before changing a fucking outlet just to be safe
Run 2 fucking wires.

[Anonymous No.16578046]

>>16578013
>but nothing's stopping the next guy along from replacing that with 2 single breakers
you guys literally have an idiot book telling you "hey idiot don't do this". idiot book tells you, hey idiot tie them together. idiot book tells you not to use the device itself to join the neutrals. Idiot safety book tells you not to work live. Idiots don't read or follow idiot books, Idiotic stuff happens. Then idiot calls the wire an Idiot cause he is incapable of accountability.
Your point about the next guy is fucking meaningless. If we are talking about someone being retarded and doing it a way they're not supposed to, why stop at a MWBC. the same moron can burn the building down running the wrong size wire, or replacing a breaker with the wrong size cause it kept tripping.
Ran with the very simple requirements your idiot book tells you to, there's nothing inherently unsafe or complicated about a MWBC. The problem is most of you barely got through high school and can't figure out how to do things that have already been solved for you and written down. And you borderline retards have the nerve to suggest you know better than the engineer just because his specs weren't directly made to make your job as easy as possible. You fuckers can taste blue for all I care.

[Anonymous No.16578095]

>>16578046
>the same moron can burn the building down running the wrong size wire, or replacing a breaker with the wrong size cause it kept tripping.
Those are 1 step fuckups that are gonna fuck over the person doing them and there's no simple safety measure you can take to prevent either.

Taking concern for the next guy along is something anyone working in electrical should do. Fuck's sake, that's the entire point behind color coding wires. Why not just use all black wires if you don't give a shit? Fuck the next guy.

>there's nothing inherently unsafe or complicated about a MWBC
Disregarding the risk of a dropped neutral frying the circuit, which doesn't go away no matter what. Ass-hat.

>And you borderline retards have the nerve to suggest you know better than the engineer just because his specs weren't directly made to make your job as easy as possible
If you claim to be an engineer and are against trying to make shit harder for idiots to fuck up, you're a fake ass engineer. Idiot-proof might not be a real thing, but that doesn't mean you deliberately give them opportunities.

[Anonymous No.16578097]

>>16578046
>>16578095
Oh, and changing out outlets isn't something only fucking electricians do. That's part of regular building fucking maintenance any business/homeowner might fucking do. If your position is you don't give a shit about the safety of your own damn end users, fuck off and die.

[Anonymous No.16578121]

>>16578095
>no simple safety measure you can take to prevent either.
Nope. stopping unqualified retards from from touching electrical systems must be impossible. absolutely nothing you can do....moron
>Fuck the next guy
if the next guy is unqualified to touch something that can kill people, yes fuck em. If he was qualified, there's no issue.
>Disregarding the risk of a dropped neutral frying the circuit
dropped neutral fucking how??? MWBCs must have an interlock. A device cannot be used to bridge the neutrals. You are not allowed to switch a neutral. how the fk are you going to lose a neutral? the fucking wire disappearing? making the world's most shitty joints? when a MWBC is ran like it's supposed to be, the next guy should be able to tell what he's working on.
> If your position is you don't give a shit about the safety of your own damn end user
I don't give a fuck about people fucking around with shit they shouldn't and finding out. If you hired a fucking handyman to do electrical work and he fries your computers, get fucked. If you're a homeowner trying save $100 and willing to risk your home for it, get fucked. If trade schools are lowering their standards to allow retards to make their way through, i hope they get sued, then get fucked.
If you follow all rules for running a MWBC, and the guy after you does for modifying it, there's zero fucking problem. if you got shocked, you probably deserved it moron. unfortunately, it almost certainly wont kill you.

[Anonymous No.16578188]

>>16578121
>MWBCs must have an interlock
Wires have 2 ends, dipshit. Shared neutrals run through building wiring. You aren't just worried about the fucking box. Honestly you not even realizing this just outs you as having no god damn idea what you're talking about. Best case scenario, there's still at least 1 failure point somewhere in the wall where the 2 neutrals come together. Worst case scenario the neutral's got multiple fucking connections along it. One god damn loose wire nut when someone's doing maintenance and the whole god damn circuit goes from 120V to 240V.

>If you're a homeowner trying save $100 and willing to risk your home for it, get fucked
Ah yes, the "changing an outlet should require calling an electrician" argument. You get fucked, ass-hat. That's neither reasonable nor realistic.

[Anonymous No.16578237]

Because the source emfs are 180 degrees in phase you can get equivelant DC circuit when L1 is at highest tension.

Kirchhoff current law:
[math]I_1=I_2+I_3[/math] (I chose the I_3 direction, does not matter as it will just be negative if chosen wrong)

Kirchhoff voltage law:
Upper loop: [math]U_1=I_1*R_1[/math]
Lower loop: [math]U_2=I_2*R_2[/math]
Immediatly we see that they can be treated as separate entities as do households actually do.
Total loop: [math]U_1+U_2=I_1*R_1+I_2*R_2[/math]
(Absolutely redunant).

Solving [math]I_3[/math]:
[math]I_1=I_2+I_3[/math]
[math]I_3=I_1-I_2[/math]
[math]I_3=U_1 / R_1 - U_2 / R_2[/math]
Since [math]U_1=U_2=U[/math]

[math]I_3=U (1/ R_1 - 1/ R_2)[/math]
and if the lamps have same resistance
[math]R_1=R_2=R[/math]
[math]I_3=U (1/R - 1/R)=0[/math]
and we see that current flows only in the great loop.

This does not mean there would be possibility to short circuit 240 Volts unless you would short circuit simultanously at both resistors and the neutral wire at middle would be broken.

[Anonymous No.16578396]

>>16578188
>Wires have 2 ends, dipshit
i gave multiple requirements, dipshit. the joints are only accessible in the panel and in device boxes. in the device boxes, you Must pigtail. changing the outlet doesn't require taking the neutral aparts. So what's the failure point? making a dogshit joint? wire nuts are just insulators not bridging points. even then, not that hard to tighten a wire nut, if you're not a fucking retard. Wires don't fucking disappear out of nowhere.
>Ah yes, the "changing an outlet should require calling an electrician" argument
no, it's the "if you work on something without understanding it's unreasonable to expect nothing to go wrong" argument. or FAFO for short. Something not being designed for the lowest common denominator, when being serviced by the lowest common denominator is not a design goal, is not a design failure. A mass production EV that takes an electrician every time you want to charge it is a shitty design. A camshaft that requires taking the motor apart to access is not. A dildo is designed to be taken right out of the package so you can easily go fuck yourself, and you should.
>>16578237
This is much simpler with superposition. Make one of the batteries a wire, and it's just V=IR for the first resistor. second is parallel with a zero resistance path, so current is zero. Regardless the entire point is with this particular configuration you can interpret it both ways and don't know which applies to what's "really" or "physically" or whatever going on because the value predictions are the same. But they are only the same in this one case (nevermind the point that all of this is mathematical in the first place, and there is no "really". no one is fucking watching the electrons or physically looking at fields). Again, model 3 batteries in series and connect a path between any two batteries. If this was working as two resistors in series, bridging wire should have no current still. but it does.

[Anonymous No.16578442]

>>16578396
The bridging wire will have current if the resistor values differ. You have plenty simulations online where you see the current particles. Google Circuit Simulator. You can even use AC source and see how they oscillate.

[Anonymous No.16578450]

>>16578442
bridging wire will have current even if the resistor values are the same, if the bridging wire does not connect to a neutral point. like the example i gave with 3 batteries. take your own advice and simulate it.

[Anonymous No.16578469]

>>16578450
Yes but that is not real scenario because split phase splits it exactly half

[Anonymous No.16578479]

>What is physically happening here? this is a multiwire branch circuit with phases 180 degrees out of phase.

you get 240votls and the middle wire is just ground that's all. so the purpose is to get 240v from just 120v i guess. but with half the current as with 120v.

[Anonymous No.16578486]

>>16578479
cont
but specifically in your circuit i see no benefit since they are separated

[Anonymous No.16578487]

>>16578469
Since when is 3 batteries in series not a real scenario??? Who gives a fuck what split phase does in the specific application of residential power? it's entirely possible to tap the transformer at different offsets. The entire point is in this very specific scenario the two interpretations look the same. So to prove one or the other you have to see where the predictions differ. Did you even read the thread?
>Is it like the picture suggests and you have two different waves traveling independently and it just "looks" like they cancel on the neutral
>They are 240 volt in ohase and the current flows through one to another...In this you just forget the splitting and use the 240.
If the second view is right, then the bridging wire shouldn't matter. Hell, if it was right even the resistors wouldn't matter they'd see equal currents because they're in series. The entire possibility of an "imbalance" is because they are independent 120v circuits.

[Anonymous No.16578504]

>>16576989
The picture isn't correct. The current goes from red to blue also.
>>16577050
Are u retarded? It explains what the benefits are. It acts like a 240V circuit, so it uses less current which means less wire and lower voltage drop.

[Anonymous No.16578526]

>>16578487
They are not waves anon. 60 Hz is too low frequency to think it as a wave. In many inbalance situations the middle wire will have a current. But in the balance situation it will not have any current and this can be measured with ammeter. And the current is real thing the closed circuit is a real thing and the closed circuit is the great loop and the great loop has 240 V as source voltage and 240 V worth of voltage drops.

[Anonymous No.16578532]

>>16575129
>As i've heard it explained, the "currents cancel" when they both travel on the neutral and it only carries the net difference.
You have 2 currents of same strength that travel in opposite directions, what is hard to understand? And you want to call people retarded.

[Anonymous No.16578536]

>>16575129
>how are you able to derive power from these currents just "cancelling".
Because only the currents at the neutral are cancelling. The picture is retarded and doesn't show the main current between red and blue.

[Anonymous No.16578544]

>>16578526
i'm quoting the two views expressed in this thread, not myself. They are fields, the wires are just a way of directing them.
>60 Hz is too low frequency to think it as a wave
I wasn't even talking about AC, I said batteries. but this is still fucking retarded. Show me mathematically the point at which frequency is high enough to think of it as a wave. Hint: you fucking can't.
>and this can be measured with ammeter
you dont even understand the argument being made. With either description it would measure 0 in the picture. But only the first description predicts and explains the results when you vary resistance, voltages, or the bridging connection. If you disagree, address the actual points made instead of continuously restating your view.

[Anonymous No.16578659]

>>16578544
"8" loop is not "0" loop because its connected from middle. Neither "8" is two separate "0" "0" loops because its connected in the middle. "8" loop is different from these two simplifying abstractions we try to make.