Neutral Imbalance in Multiwire Branch Circuits (Two Hots, One Neutral)

[@tylerberry5704]

I’ve been asking this question for the entire 4 years of my apprenticeship and no one has been able to answer it. Thank you for taking the time to explain this 👍🏽

[@CommunityGuidelinez]

Now you further understand the importance of pigtailing grounded conductors as well, I'll bet 😀

[@linemanap]

Your apprenticeship program must really suck. This is super basic.

[@truthdefenders-]

😂 whom we’re you asking? 4 years and no one had an answer? Really? 😵‍💫. Get your money back and apply at a new school.

[@Magicman4124]

When I was a first year.. almost 6 years ago.. a Journeyman asked me which wire was the most dangerous or requires the most caution. I of course said... well it's your hot.. it's bringing power through your circuit.. I feel like this video is an amazing example of why your neutral CAN be the most dangerous. It's something to keep an eye out for before you start jumping into your project. Very nice video. 👌

[@earthtones1138]

Good stuff. 👍 For multi wire branch circuits, I've been Using breaker handle ties that allow for independent tripping but simultaneous switching Because I believe that's right, right? If you haven't already you should make a video about do's and don'ts of multi wire branch circuits. Should make for a lot of content hence my comment is so f****** long like If 2 single branchers are in one Box, you don't just tie all the whites together. And why you might find a neutral wire in the panel has turned a darker tan color compared to the other white ones. Like what can happen if you disconnect neutrals at the panel Without killing the breaker(s) it belongs to. Pig tailing neutrals at devices. And if you find Kitchen outlet Receptacle with black and red on one side, Note the tab is broke off, Separating the terminals. Labeling. How you can ruin plugged in equipment by Being really cool and working on a multi wire branch circuit while it's hot ( Or The other breaker is still on) and disconnect the neutral.

[@williambeauregard5440]

Biggest shock of my 50 year career was a neutral. Service drop, (overhead) was torn off the side of the building, laying on the ground. I had cut & taped off both ungrounded conductors. I then separated the neutral ACSR cable(overhead) from the SEU that should have run down the house. I was unable to let go. Still not sure how long I was stuck there, it seemed a very long time.

[@jamesmore2919]

@@earthtones1138 i believe thats right? how you ever get your licenses?

[@jamesmore2919]

@@williambeauregard5440 50 year career. and you working hot circuit? how you make it that long?

[@peterrose5373]

the most dangerous wire is the one you think is dead.

[@Fireship1]

This by far, is my favorite electrical knowledge channel. You explain everything to complete understanding and do it with the perfect blend of wit and humor. Thanks for all that you do!

[@cachapma99]

Love your videos. You should mock these up as examples in a lab environment, use a clamp meter and show us the values.

[@mikeiver]

Why?

[@cachapma99]

@@mikeiver I guess I just like to see these things in a lab environment, or in actual application. It's fun to see, and when I studied electrical in college, I preferred lab classes over theory classes.

[@mikeiver]

@@cachapma99 Fair enough, some can only learn by seeing and doing rather than reading. this video is more geared to the beginner rather than the seasoned tech I should expect. there is always something to be learned though.

[@schowers]

I'd like to see that as well. He's saying on a 20 amp two pole breaker if you hook 12-3 and run two separate 120v circuits off it, you actually have 240v coming back on the neutral?

[@mikeiver]

@@schowers Nope. If you have a pair of breakers, one on each phase and utilizing a common neutral between them, that only the imbalance current is returned on the neutral. So lets say that you have a pair of 120V loads, one on each phase, with each drawing 10 amps from their respective phase. The actual imbalance current on the neutral would come out to ZERO. Each load would drop 120V and the current would return from one phase to the other. Now if we leave the load on the A phase at 10 Amps and reduce the load on the B phase to 7 amps we have a total of 7 amps from the A phase being returned thru the B phase and the balance of the current being returned thru the neutral, that being 3 amps. Get it? Now there are other things in play here that I will not go into such as the possibility of excessive induced currents in a shared neutral should the loads be motors. IE: Power factors of less than 1. Mainly because I don't understand the underlying math and theory enough to speak on the subject with any authority. But the above should provide enough to help you understand.

[@KameraShy]

THIS is the video I really wanted to see. The issue is significant for me. My house was built in 1938 with a two-wire 110 volt service which fed the entire house through two fuses. Wiring is all in conduit and was all routed through ONE 4" square box. Entire house. About 30 years ago service was upgraded to 240 volt. The electrician routed a couple of additional circuits but left the rest as is. I have untangled some of it, especially after breakers started tripping. There are definitely shared neutrals remaining. They did try to save money on wiring and conduit in this post-Depression house. And residential loads back then aren't what they are now. It is great to know how this works, as I continue to unravel the wiring in this house.

[@rogermabry2816]

Dustin , I am older than you , But had to make a career / job change . I have only been a electrician for 8 years now . Learning Residential , Commercial , Industrial , So much to learn . Everyday is a learning experience . Love the way you teach . Thank you .

[@mfiels]

Great explanation. MWBC is what got me interested in how residential electrical works. I got shocked on the neutral when trying to change a light fixture, because my breakers were installed before the handle tie requirement, and I only had one flipped off. Then I did a bunch of research to figure out why that had happened, and along the way became very interested in how this all works.

[@MrGatlin98]

I tried to change a light fixture and assumed turning the lightswitch off would disconnect the power. I felt a weird tingle but proceeded anyway. In my defense, I was about 13 or 14 and didn't know to turn off the breaker.

[@mrtechie6810]

Never assume the power is off; always use a tester to verify! I then brush the wire with my hand as an additional check before grabbing it.

[@mmoser9483]

@@MrGatlin98 Tesla did a much better job at making sure you understand differentials, and that all current eeeks to seek a balanced state, and that means retruning to ground.

[@MoneyManHolmes]

I once got shocked by a neutral because a 3 way switch on the circuit had neutrals from a different circuit in one of the 2 switch boxes.

[@rovidius2006]

​@@mmoser9483 Not always , two hot legs would choose to run most all current in between them rather than going through the ground ,current preffers to equalise the highest of all differentials .

[@daytonturner2265]

This is gold man! Saving me years of class and helping me understand exactly what I’m doing out in the field as a helper. Thanks

[@stevesargent4269]

Once again you have taken something that in my days of schooling seemed hard to grasp and explained it simply and perfectly. Keep it up.👍

[@KevinCoop1]

Dustin, Multi wire branch circuits in dwellings can be with 2 pole breakers or handle ties manufactured by the same as the panel. The reason NEC started requiring them is not for overcurrent protection. It is for maintenance work to ensure disconnection of all hots on common neutral. Really good video! Keep it up! Respectfully, Kevin

[@twestgard2]

Wouldn’t it be for both?

[@KevinCoop1]

@@twestgard2 If you are sayin both disconnection and overcurrent. A two pole breaker will trip both. One for overcurrent and other nuisance trip. The handle ties will disconnect both, but overcurrent on one side will only trip one. That is because it was not the reason.

[@robertlaw4073]

Makes sense... once you disconnect one side of the run, the other side will operate just like a standard 2-wire run. I was wondering about this as my home has 3-wire runs but they are not tied together. I suspect because the work was done before this was part of the NEC (added the rule in 2008 I believe?) so it's nice to know it wasn't for operational safety, but for service tech safety.

[@jonclark1288]

@@KevinCoop1 I agree with everything you said, however, requiring a handle tie on single pole breakers means that you're basically forced to have the two breakers right next to each other. This ensures that the breakers are on different hot legs, which prevents the neutral from being overloaded. Without the handle-tie requirement, one could put the two single pole breakers in any random spot in the panel, and could possibly put both breakers on the same hot leg, which could overload the neutral. So in that sense, requiring handle-ties kind of DOES prevent overcurrent (on the neutral).

[@KevinCoop1]

@@jonclark1288 I agree with you that it does stop neutral overload from being on the same line, but my statement was the reason it was put in NEC was not because of your instance, it was originally for commercial work with multi wire branch circuits feeding portable office partitions. I looked up the in writing proposal to the panel and also talked to a person on that panel that I used to work with. A maintenance worker got shocked while working on the furniture. From there, they decided the next cycle to require handle ties or multi pole breakers for all multi wire branch circuits. So again, the reason why it got put in NEC was not overcurrent protection. Respectfully, Kevin

[@willschultz5452]

Perfect explanation!! I had a situation at a convenience store where they used a single neutral on two 20 amp circuits on the same phase, it melted the neutral wire at the wire nut inside a junction box. The customer complaint was the smell of burning plastic near the cash register. Traced it back to a Junction Box underneath of the counter. The neutral wire was glowing orange at the wire nut and all the insulation was burned off. 😂

[@throttlebottle5906]

someone moved breakers around in the panel and didn't know to check for shared neutral/phase.

[@pttthhh]

yeah that's reallly funny... -sarcasm

[@BenKochendorfer]

Coming through clutch with the super hero moves that day! Hope you were well rewarded for saving the business from burning down. 🔥

[@gerardotorres7904]

@@throttlebottle5906 so that circuit cant be on the same phase? It has to be a 240v circuit on separate phase?

[@throttlebottle5906]

@@gerardotorres7904 correct, if it's on different phase's the current is mainly flows across through the two devices and balances out, with any remainder going back on the neutral conductor. if only one device is powered on then all of it's current will go back on the neutral. say it's a 20 amp circuit, then only up to 20 amps max will go back on the neutral. now if it's wired on the same phase, and both 20 amp breakers, the current will not balance across the devices and you'll end up with max of 40 amps trying to go back on the neutral! that would obviously be double what the conductor is rated for, overheat and start to burn. I've ran into many times over the years. it's now NEC code to have a two pole breaker on any shared neutral circuit, that keeps them on opposing phases and ensures the whole circuit is dead when breaker is off, that way you wont get shocked off the neutral, nor overload it.

[@thelastword7203]

I listen to your videos all day at work and now I found one to listen to to help me with my slump during homework!

[@melkortdl2010]

As mentioned below a few times, there are some NEC regulations, including that both circuits on a MBC must be on a single 2-P breaker at the MAIN panel and and all sub/intermediate. The biggest risk I've seen is where Handyman/ Homeowner Joe moves one of the breakers in the chain not knowing it's part of a MBC and suddenly you have an overload on the neutral that neither breaker detects. The risk of hot neutrals is also a real thing too if you've ever been buzzed by one. That really makes for a fun troubleshooting experience in an unknown location.

[@rmrieee9748]

As soon as any imbalance happens that amount of current flows on neutral.

[@1575murray]

I was surprised when I replaced some outlets in my mother's apartment and got shocked by the neutral when I thought I had the power completely off. It turns out that the NEC did not always require the use of a 2 pole breaker for an MBC and the electrical contractor used two separate breakers on two separate phases instead. Now I know that I have to shut off both breakers when replacing any outlet on either leg of the MBC.

[@ScrewThisGlueThat]

Dustin, I came back to watch this again today because you gave me so much to think about my mind was going crazy today while driving to work and thinking about this. You are a truly awesome teacher and I really thank you for everything your teaching in these videos.

[@mattrob15]

I've learned more from you than I have in school lol. Thank you for what you do. I wish I could work side by side with you for just a couple months.

[@Five0Music]

Your videos are the best electrical system content I’ve seen on KZbin, I’m subscribed! I wired two “back to back” bathrooms (they share a common wall) on a 12/3 circuit to ease the long run in a very low attic space. My old (1952) house has a shocking number of loads on each old 2-wire cloth covered romex circuit, and I am breaking them up while replacing the wiring as I redo each room. After watching your video, I went back and verified each circuit in the 12/3 was on a different power leg (they were), so I’m feeling good on that one. But now, considering the potential for doubling the load on the neutral if miswired, I think I’ll just stick to single cable runs where the neutral is just carrying the one circuit. I was ok, but your video made me go and make sure I was, and that’s the definition of worthwhile content. Excellent work!

[@mbburry4759]

If it's hard to access and both circuits need seperate neutrals, you could use 12/4,

[@dankelley9361]

Excellent explanation of phase relationships that unfortunately most people have trouble understanding!

[@watchoutbelow]

My electrician told me that I had a multi wire branch circuit wired house. I found this video and it made it all so clear. Thanks.

[@28misterluna]

Thanks for the video, as always you explained it in a way that I understood. I just started working as an electrician and your videos have helped me a lot.

[@phantom21629]

Why do all of your outlets look look like they're extremely worried? 😂 This is a great explanation of these situations. It gets confusing when you add another phase when you don't understand how phases work. I've learned a tremendous amount from your videos. Some of the things I already knew what would happen but never knew why. Thank you for your time and effort to educate us.

[@TheirishkingadventuresBlogspot]

This is a huge help, I've been struggling to figure out how this all worked in school right now. Thanks!

[@johnbayliss1098]

Never stopped those videos only one thing to say excellent

[@SteveWhiteDallas]

Great information. I just have a caution to add. This is a split single phase system (often referred to as 2 phase.) The secondary winding on the transformer puts out 240 volts from end to end. There is also a center tap (a wire connected to the center of the secondary winding.) From either end to the center tap is 120 volts. The power company grounds the center tap. That is the neutral. It is a grounded conductor, but not a negative wire & not a safety ground. The push and pull is making reference to frequency. In the USA, the frequency is 60 Hertz (cycles per second.) So, 60 times per second, the red & black wires cycle from 0 volts to 120 volts. When the red leg is hot, the black leg is not. That allows 2 circuits to share a neutral at full capacity as long as each circuit is connected to a different leg. As mentioned, the neutral carries the difference if the 2 legs don't have exactly the same load (and in 120 volt circuits, they rarely do.) That neutral serves one more purpose. If one leg becomes open, then the neutral will carry the full load of the other leg. However, Multi Wire Branch Circuits (MWBC) have a danger you should be aware of. Regardless of the load on either circuit, you DO need the neutral wire, even if it carries no load. It's the neutral wire that renders two 120 volt circuits from the 240 volts (just like it does at the transformer.) Every MWBC must have a bonded neutral connected to the neutral of each load at the point where the 240V circuit is split into two 120V ckts. That creates two parallel 120V circuits. If the neutral wire becomes unbonded (disconnected) from the breaker panel, those two parallel 120V circuits become two 120V circuits in series which creates a single 240V circuit & 240 volts will pass through both circuits and everything connected to them. That's fie because the 2 circuits are resistance in series. But if the resistance of leg "A" is increased by turning something off, without a neutral, leg "B" would require more current than leg A. That current would be pulled through leg A since there is no neutral. When resistance is increased, but the current from leg B remains the same, the result is a voltage increase on leg A. That will result in a surplus of voltage on the neutral of leg B. (The neutral will have more voltage than the hot can cancel.) If that happens, damage to devices connected to both circuits will occur and it's likely to be beyond reasonable repair. Always turn off the appropriate breakers before loosening the neutral of a MWBC. (Think of two AA batteries. If you connect negative to positive on two 1.5 volt batteries, you get 3 volts. If you connect the positives together and the negatives together of two 1.5 volt batteries, you still only have 1.5 volts. A MWBC is exactly the same, except it's AC, not DC so there is no negative and positive, and don't even think about connecting the 2 legs together. I know, but I had to say it just to be sure ...) Unrelated, but safety is always worth mentioning: The biggest danger of getting shocked by 120 volts occurs when a hot wire falls and rests on you or you fall onto or into something hot (such as an open bus). If you bump it, you can fall away from it but if either you or "it" comes to rest while you're in contact with it, you're in trouble. Don't fool around with hot panels alone or push a metal fishtape into a panel.

[@jwick4320]

Well said!

[@satejr2able]

This is great, I’ve been asking this question and no experience electricians can answer this. I’m very technical with questioning everything and no one can answer. Great job Dustin

[@arthendrickson4860]

It might help to include waveforms in conjunction with push/pull to show the addition of two phase waveforms adding up to zero in one case or 5 in the other case.

[@spdglez6663]

Easy to understand from a Working Electrician and Smart Person. Thank you Man.

[@MrFitness94]

Great vid. Would have been good to add: if no loads are attached to the opposite leg it acts like a normal circuit, the dangers/behaviours of an open neutral in these circumstances, and using a split recep as a visual

[@teardowndan5364]

I lost two computer monitors and one PSU to an apartment with bad neutral. One leg could dip to 90-100V L-N and the other surge to 140-150V measured at the breaker box. The situation improved significantly (125V max, 110V min) after the power company changed the transformer a few months later. The transformer must have had a broken neutral and the building still have a loose neutral between the transformer and unit panel.

[@aristeo2183]

thank you for your videos. it helped me chase down a problem with with an open neutral where two branches were shearing the same neutral. The master bedroom outlets and bathroom lights were out, found the problem in an outlet in the kitchen where a 12/3 conductor came in from the main panel. This is where the circuits branched off. The neutral from the effected branch was loose from a bundle of neutrals wire nutted together. Connected neutral and corrected problem, lights and outlets working again. Thank you.

[@chasestone2124]

Man i love these videos ... keep them coming .. so helpful and educational

[@ShelbyGT5OO]

After much googling, this is the Best video ive seen to explain this. Thank you!

[@wizengy]

I show the Black phase as a sine wave and the Red phase as an inverted or minus sine wave (-). The current for the neutral is the addition of the two. In no case is the addition of the two greater than one phase and if they are balanced they perfectly cancel out leaving a flat line. If one phase is 5A and the other 10A then you will get peaks of +10A and -5A leaving a 5A current in the line.

[@RUFFFHOUSE]

Nobody explains this stuff better. Thanks professor Dustin !

[@deathhippie6220]

I really appreciated this. I had a few run ins with this situation recently before I seperated the supply lines. I actually have a bigger problem at my nephew's house. He has 3 or more breakers with a common neutral. I wonder if you could help me explain to him and his father how scary of a problem this is, since me telling them "this is really bad" isn't helping.... they seem to be of the mindset that" well, it's working, so why me worry?" Maybe you already made a video of it. Thank you so much!

[@robc7323]

Great explanation of MWBCs. i have an older house and wanted to install an appliance in the basement on an existing MWB circuit. I wanted to properly calculate load on the circuit and get an idea of how the circuit would handle a possible unbalanced load on a shared neutral. Mentioning how it is similar to how two single circuits terminate in the panel except the neutrals are tied together before the panel and how the different phases on the two legs cancel each other out on the neutral and the unbalanced difference is what flows through the neutral was also a big help. The best explanation i have come across.

[@intercity125]

Kirchhof's first law. The sum of currents flowing into a junction must be equal to the current flowing out of it

[@p39483]

Yay. Opposite phases of equal current sum to zero, thus no current in the neutral.

[@huejanus5505]

Kitchen counter plugs are usually wired with a 14/3 wire, the tabs between the outlets is snapped off. Red wire one side, black on other side and the white does both. So you can use a toaster oven and a coffee maker at the same time on the same plug. How is that any different than this, isn’t that an unbalanced system? If it is then why do they even make 14/3 wire?

[@intercity125]

@@huejanus5505 The neutral will still only carry the imbalance back. Of course if only one of those is operating then that will be the full current...

[@AnthonyTong555]

@@huejanus5505 As long as the black and the red are going to different phases on the panel this is ok

[@jefffree6990]

Yes that makes sense, especially when he showed the diagram with the resistive loads. Then you can calculate the current flow. Overall this is a very helpful video. But simply labeling that node with arrows showing 10A in and 15A out means the extra 5A must be coming in on the neutral would have saved a lot of hand waving A diagram with "10 amp loads" was shown at one point , but that is a bit vague and misleading. it suggests you might be able to just look at the labels of each device. In practice that gets you in the ballpark of what the balance is, but to really understand what is happening, and why, you would have to know the effective resistances. That diagram with resistances makes more sense to me.

[@brianjmortensen]

Awesome explanations ! Thank you for using correct terms with regards to “Voltage across”, “Current through”, and “Resistance of”.

[@luckyhiker3434]

Justin, this was a real good lesson for sure. I ran a multi wire branch circuit some time ago sharing a neutral between a lighting circuit and a dedicated microwave circuit. They are two separate phases but I used two breakers that operate independently of each other. Now I recognize the danger: I could open a breaker for the lighting circuit but the microwave circuit would still be feeding that circuit through the shared neutral. I think I need to abandon the the sharing idea and pull a separate cable. Your thoughts?

[@lamartatum9908]

Just add a handle tie connecting the two breaker handles. That way, you trip both at the same time.

[@maskedamender]

I'm a electrician who is a real visual person when I listen to somebody else, & so at around 14:36 I got a visual from listening to you that helped me figure out how to explain to somebody who asked me why you can't have two hots on the same leg sharing a neutral, & the visual I got was: picture two people on the same side of a lightweight wall (calling each side or wall a leg) pushing with 20 lb of pressure each (20amps) on the wall versus.... one person on one side of wall and one person on the other pushing 20 lb of pressure each side....& then the thin wall just safely spins round & round with them pushing, BUT the wall with two people pushing on the same side... the wall falls over & they fall on flat on their faces with the wall!!! 😏 I don't know I can't help what visuals I get when I hear great teachings!!! 😎

[@stevesideris8364]

You need an oscilloscope. Easy to see how current cancels with opposite sine waves.

[@griffmustard]

Exactly !! Also, if you pause the video at, lets say (8:42), and have a look at the two pink arrows, if you can visualize the top pink arrow, with the arrow head at the neutral wire, you can see that when both arrow heads are at the neutral wire, they point in opposite directions, meaning the black wire is at +90 and the red wire is at -90, and their currents are at (+10A) and (-15A), respectively. And that is how you end up with (5A) on the Neutral.

[@mattbaker6587]

@@griffmustard thank you for your contribution!

[@griffmustard]

@@mattbaker6587 Matt, you're very welcome !!!

[@spruce_goose5169]

And if you yanked the neutral connection with uneven loads, one load would burn brighter (see higher voltage) than the other (the higher resistance load). When equal loads, they work fine with no neutral at all.

[@icevariable9600]

Doesn't help when most electricians don't know what the X & Y axis is or how a sin wave pertains to electricity. They just parrot back what they see on YT without understanding it. A cartoon would be better.

[@ChristopherBurtraw]

Once I figured out that a common neutral will only carry the maximum load of an imbalance, which is equivalent to the maximum load of either hot, it all made so much more sense. I understood this before this video, but "one pulls while the other pushes" is a great way to explain this to anyone else so I still learned something useful for watching. Thanks!

[@KevinBenecke]

I actually have this in my home. They are mostly on the circuits that feed the upstairs probably because they were to lazy to fish proper wire to feed everything. My house was built back in 1907 and originally had knob & tube wiring. When it was rewired, they fished this type of wire to the attic to feed the upstairs rooms.

[@Ariel1S]

There's nothing lazy about this, it's a perfectly fine way to wire things.

[@johnmartin1024]

Thank you Dustin for such a good video. I am trained as an Electronics Technician. I never realized how important A.C. theory is in residential home wiring. My guess is that the Red hot and the Black hot are 180 degrees out of phase - and that is how they achieve 240 Vac in the panel. John M.

[@hunterkuhlmann3647]

Love your videos! Please keep it up you and your crew do amazing!

[@awkerper]

Many thanks, this is great to know! Now I understand why my generator transfer switch manual said the neutral can be overloaded if you run one side of a handle-tied branch circuit through the xfer switch and not the other side. You have a very effective way of explaining it with the push-pull concept between phases. 😊

[@ForeverZeroAngel]

Would love to see you make a video on balancing out a panel between the two legs of power

[@alexknight7191]

Great explainer! This becomes especially important if you have tandem breakers in your panel. The house I just bought at the end of last year has a number of them and most were OK but a couple were doubled onto a MWBC. It's so easy to avoid by simply not sharing a single tandem breaker for a MWBC (should be split and tied) and yet someone did it anyway. I've found a few other "Why would anyone do this!?" surprises along the way. Yay for old houses and shoddy work!

[@hoodratrc]

Should’ve talked about what happens if you lost the Neutral in the multi wire circuit with the imbalance loads

[@deandred712]

Doesn’t it act in series causing the potential for one load to be burned out due to kirchoffs law of current pretty sure the possibility of one load not receiving enough amps because source is supplying lower current for the lower load also exsist just depends which is connected closer to source

[@deandred712]

Year one sparky here so could be so so wrong ☠️

[@thomasprovencher4611]

A friend of mine has this happen to his entire house cause the neutral was lost at the transformer supplying his home. Nearly every piece of sensitive equipment in his home died, including the brand new central AC system as all of the computers in those things need 120.

[@nlee5034]

Woooo!! That’s bad!! Anything connected to those circuits, get 240… er’thing gone.

[@declaneric]

Excellent explanation of the balanced load concept. For any who need a practical application of this, think of how you run wire. Running romex simplifies things sometimes, because neutrals are run with the hots. But instead, say you're running wire in EMT instead of romex. You can run nine 12-gauge wires in 1/2" EMT. So you decide to pull five circuits to a J-box, then branch off to different areas. So in the EMT, you have 8 wires: 3 Black wires (A-phase circuits 1 / 5 / 9) 2 Red wires (B-phase circuits 3 / 7) 3 White wires (neutrals) Remember, phases alternate in the panel, so 1-3-5-7-9 in phase-notation is A-B-A-B-A | So to do this and have balance, you HAVE to pull three White wires with the five circuits, one neutral for each "pair" of phases A-B, plus one for the extra A-phase circuit. So circuits 1 and 3 can share a neutral. So can 1 and 7. Same goes for 3 and 5 or 3 and 9, and so on. As long as the 2 circuits sharing the neutral are alternating phases and NOT same phase, you're fine. The third neutral is for the extra circuit in the run. If 1 and 3 share a neutral, and 5 and 7 share a neutral, circuit 9 is still there by it's lonesome. If you tie circuit nine into the neutral for either of the other two pairs, you're overloading that pair's neutral, since 9 is in phase with both circuits 1 and 5. So you HAVE to run a third neutral to cover circuit 9. | And I explained all this to make this critical point: In the J-box you hit before branching off, YOU CANNOT TIE ALL THREE NEUTRALS TOGETHER. This is really important. In this example, three whites aren't ONE neutral run, it's THREE. So the neutrals have to stay separate in the box. If circuits 1 and 3 leave the j-box to one room, their neutral is wirenutted to one of the neutrals in the J-box going back to the panel. Circuits 5 and 7 leave the j-box to another two rooms, their neutral is wirenutted to the second neutral in the j-box going back to the panel. Circuit 9 leaves the j-box for another room, its neutral is wirenutted to the last neutral in the j-box going back to the panel. So there would be 3 wirenuts in the j-box, one for each neutral run, NOT three neutral runs all wirenutted together with their branch-offs from the rooms the circuits feed. And say circuits 1 and 3 go to a room next to a room fed by circuit 9, so you run them in the same pipe from the j-box towards those rooms. Since circuit 9 has its own neutral, you have to run 2 neutrals in that pipe to cover the circuits properly. And if you set another j-box before you get to the last room, you can't tie those 2 neutrals together either, they have to stay separate all the way back to the original j-box. And those two neutrals will be wirenutted to separate neutrals in that original j-box going back to the panel. Can't stress this enough, NEUTRAL RUNS STAY SEPARATED FROM EACH OTHER. The number of times I've seen a box full of neutrals all tied together with 3 or 5 circuits in the box...... Oy. It's not just a code violation, it's a straight fire hazard - AND, not mentioned very often, you can create quite the magnetic field in a box when you mix a bunch of neutrals from a handful of circuits like that, which isn't safe either. | I'm explaining this with EMT and loose wire because romex sometimes makes it too simple by always having a white wire plus a color, or a white wire plus two colors, depending on the size of the romex, and romex is always its own run, you don't pull all the circuits together in one pipe. So it sometimes takes the thinking out of the process, whereas running loose wire-pulls in EMT forces you to make sure you understand what you need in the pipe. That said, if several romex runs from the panel all hit a j-box together, make sure you label the circuit numbers on the romex in the j-box and make sure you're not splicing neutrals that don't belong together. Labeling in a j-box it critically important just for that, if nothing else. | What Dustin just explained is the science and the math of WHY it has to be that way. He also did a good job of explaining why the neutral wire isn't simply a "return" to the panel, that it serves an important function in balancing the system, and how that works, scientifically speaking. Great video.

[@russellboedeker2070]

A very complete and on target explanation. A minor correction in terms. A residential electrical system is single phase. The red and black are at different polarity, not different phases. Red is positive polarity (peak sign wave) and black is negative polarity (trough of the sine wave). That's the push/pull effect on the single-phase ac system. [yes, the sign waves flip back and forth, but red as positive polarity and black as negative polarity is how the NEC describes them in 200.6 & 201.5]

[@elizabethchatfield695]

Thank you for this. Our 1976 house is loaded with 12-3 shared neutrals.

[@99andrianmonk]

Missed an opportunity to do what you have done well on other videos that helps make sure things are done correctly - reference code and talk about what needs to be done to make sure code compliant and not creating an issue inadvertently. My experience has been that what you spent only a few minutes talking about at the end - issue with MBC on same phase - is what's typically done and hence create the potential for too much current on the neutral. Nice to know the theory but it would be beneficial for a simple explanation of what should be done to properly wire a MBC,

[@roadie193]

My company does multiwire branch circuits for most of their home runs. Holy shit that’s a lot more complicated than I thought. Thanks for the vid

[@supercooldude824]

Hey Electrician u , can you make a video on how to read wiring diagrams (if you haven’t already) I’m having trouble with that in school thanks!!!! Love your vids

[@ramandeepsingh391]

You are a master Dustin ! Thank you for help Love from 🇨🇦

[@NoName-ef3jq]

Hi, Dustin. Could you make a video about phase displacement in transformers? I've been a bit confused about it in class, and we've been connecting transformer banks in parallel, thankfully all of my connections have worked and nothing blew up. But I'd love to see this topic in depth.

[@randomlife7935]

IF you really want to fully understand phase displacements in transformers, it is best to study phasor algebra. Using geometry to explain how the sine waves react is not going to be enough.

[@NoName-ef3jq]

@@randomlife7935 I'm taking a technician's degree, I asked my instructors and they're never gonna teach that to us in depth, just basics. So, I'm trying to find out a dumbed down version of it, basically.

[@spruce_goose5169]

@@randomlife7935 I think there actually is a fairly sound geometric representation using triangles. I will revisit this tonight and see if I can pull it together in words. Or link to an image/video.

[@griffmustard]

This is also known as the Vector Group of a Transformer, and it details the Phase Displacement/Shift between the Primary and Secondary terminals of a Transformer, connected in (Delta-Wye) or (Wye-Delta). In any displacement situation, you will always have a Lagging or Leading condition between the Primary and Secondary. On a Transformer Data/Name Plate, you might see (Dyn1), (Dyn11), (Yd1) or (Yd11). This is indicating a Shift of (+30 degrees) or (-30 degrees) between the Primary and Secondary. Often times you might see the face of a Clock being used to show the Phase angle. When the Long Hand or the Short Hand of the Clock (I forget which one) shows (11), it indicates a (+30 degree) shift, and when it shows (1), it indicates (-30 degree) shift. Its not a hard concept to understand, it just takes a little researching of the topic, to put it all together, and to have it make sense.

[@deang5622]

No, what he is talking about folks is connecting transformers in parallel...it's very easy. He's talking about the direction of the windings and the direction in which the magnetic field is flowing. The direction is typically indicated on a circuit diagram by a dot placed at one end of the coil symbol. Now on a single transformer, they will wind both the primary and secondary windings in the same direction, so that a positive voltage applied across the terminals will drive a current through the primary and magnetically induce a voltage in the secondary coil which is of the same polarity, such that a positive voltage in gives a positive voltage out on the secondary. Now, when you start connecting transformers in parallel and in series, you need to ensure the same principle is observed. Otherwise you are going to be in trouble. Look for a polarity identification mark on the transformer to indicate which way the coil is wound. It might be on or near to the connection terminal for the winding.

[@bilmoe5856]

Love this one. Best description of why you must split passes if you share a neutral

[@tomhargreaves8820]

I'm not an electrician, but I play one with my home and equipment, and have for 50 years. I try to understand and follow code and best practices and your explanations help a lot with techniques and how and why. I recently had a licensed electrician looking at my panel to give me an estimate on some extensive work. I have one 12-3 w/g cable connected two 20A breakers on opposite phases feeding 2 different circuits, just as you've described here. He called this an Edison circuit and said that Edison circuits are no longer allowed. After seeing your presentation, I'm wondering about his statement; are these circuits no longer code? Thanks for doing Electrician U!

[@joatamonk]

While I'm not an electrician, as far as I can tell in the current NEC code a multibranch circuit (Edison circuit) is permitted so long as both hots are connected to a Tandem Breaker. This ensure that the hots are on different phases, and that if one circuit flips it takes out the other circuit that's sharing the neutral. There are also rules on the device side that the neutrals must be pigtailed together before the devices, so that the neutral is not dependent on the device. (No daisy chaining, must have the neutral split into independent wires to the device after you split your multibranch circuit back into two 120V circuits with the shared neutral.) Now, you're state may have different rules that supersede the NEC published rules, as well as sometimes local municipalities have ordinances that further restrict wiring.

[@jonclark1288]

@@joatamonk you cannot connect a multi-wire branch circuit to a tandem breaker. I think you meant to say double pole breaker, which is entirely different. Multi-wire branch circuits must be connected to a double pole breaker OR to two single pole breakers that are handle-tied together. This ensures that 1. The breakers are on different phases so as not to overload the neutral, and 2. To ensure that if you have to turn the breaker off to work on the circuit, both hot legs are dead. Now if you're using 2 single pole breakers tied together, if one breaker trips, the other will NOT necessarily trip (a breaker can trip without the handle physically moving). This however, is NOT a safety concern. It's totally ok to have the other phase powered even if the other one tripped. If there was a problem with the other phase staying energized, then that breaker would trip as well. That's actually a benefit of using single pole breakers handle-tied over using a double pole breaker.

[@tomhargreaves8820]

@@joatamonk Aha! Tied-together breakers and no daisy-chaining make good sense. Thanks!

[@Sparky-ww5re]

My sister lives in a tract home built in 1995, pre-AFCI. her kitchen is wired with 12/3 NM protected by a double pole, 20 amp GFCI breaker (EXPENSIVE!!) Her boyfriend called me one weekend because he couldn't get the breaker to stop tripping after he replaced the traditional outlets with the decora style, to give the kitchen a more updated look. After he said there was a black and red wire on the old outlet, but after checking all the connections making sure nothing touching, I said, yes something IS touching, the tab joining the two halfs that you forgot to break. 😂😂 Fun times.

[@BlackHoleForge]

Electricians remind me of Thanos. As with all things there must be balance.🤣

[@jimithang3]

I ran across this exact situation in my house. The hots were on red/ black phases on the panel but weren't combined with those little breaker locks so i was getting phantom current on my neutral at an outlet and i was like WTF. This explained it so much more deeply than i figured out on my own. I gotta thank you . Been a long time watcher but this was so exactly what i was up against and explained so in depth that i gotta say hats off on this one.. well done and thank you!

[@luckyhiker3434]

Really good! Now I need to change something in my house to correct what I did 20 years ago. This old Pushmatic panel does not have alternating A and B phases on each row of breakers. Example, every breaker on the left hand side is on A phase and every breaker on the right hand side is phase B. Unfortunately I did not realize this when I added the multi wire branch circuit.

[@RVSparky]

I'm an RV electrical specialist. 50 amp RV'S connected to 240v 50 circuit. Nothing in them uses 240v. It's just 2 branch circuits. Neutral failures are very common and with imbalance in the RV like a low resistance water heater on one leg and high resistance electronics on the other leg ultimately the higher resistance stuff gets hit with nearly the full 240 volts and fries. I replace a lot of damaged equipment due to such.

[@weyfastwhitee]

Love your videos. Did this because it made sense in my head when I built my home, I'm so relieved it won't burn the place down. 😅

[@tiggeroush]

Multiwire Branch Circuits NEC 210.4 and Multiple Branch Circuits NEC 210.7 sound the same in the code, and have the same breaker requirements but are different. Good job on showing and explaining Multiwire Branch Circuits. thumbs up.

[@michaelwade9199]

I think sometimes I overthink this stuff and make it more complicated than what it is but you did a great job of laying this out it's kind of help me put it together thanks

[@dustinboyce25]

As always, very well explained. I was going to make a comment regarding the fact that a combined or split neutral return path on a center tapped 240V connection has no impact to the overall electrical circuit, but you got there at the 12 minute mark. I like that you demonstrated the danger of the single phase common neutral circuit as well. I think there is more here that could be explained to help people understand why they get a poke off of the neutral, but it might be a bit much for one video. Thanks again for an understandable and well spoken video that will make sense to the general electrical worker public

[@j.d.1488]

Very nice explanation. As a young apprentice without knowing theory, we were always taught to balance the panel. Always had to make sure all 3 conductor cables from panel had each hot on a black and red when neutral was shared. This will clarify for many young apprentices. The push and pull is something you don't realize. Most may think of branch circuit behavior more like DC. Mike Holt doesn't have Jack on you. LOL

[@robertcromwell9736]

Very nicely done. Presented a concept that most have never even though of.

[@tomTom-lb5cu]

I’ve been thru multiple classes in votec for hvac electrical and you teach excellent . These are great refresher courses and I’m learning and understanding so much more every time. Thank you so much. Electricity is so fascinating.

[@chrisallen7512]

I’m going into my second year in the JATC, this helps a lot! Also, if you bald fade your sideburns into your beard, I think it would be a much cleaner, crisp look…just my opinion, I have been subscribed to your channel years and love seeing you evolve. Wish you were a teacher at our JATC!

[@calebcotter2850]

Thank you so much. I could not find an answer to that question. It’s been driving me crazy for a long time.

[@David-uk1kb]

Thank you for explaining this. I consider myself an amateur electrician (Yeh, I know, a little knowledge is a dangerous thing). I have tried to educate myself with electrical code books and the internet before I do anything stupid. The balancing thing was like an a-ha moment where it all makes sense now. Thank you for this information.

[@tunaman2200]

Thank you for the very clear explanation!

[@vince6829]

Great explanation. Thank you for sharing your knowledge.

[@BenKochendorfer]

RESPECT! Thanks for ALL the years of sharing simple ways to understand complex problems. Your doing a Great Job! Thanks for sharing your Journey through the trade! Best of Wishes Brother

[@neftalirosado6167]

One hot , one neutral !! Correct balance!! Thanks 🙏🏽

[@ronaldviens7862]

The operative function here is that both phases are 180° out of synch with each other. Any imbalance is resolved in the neutral, and is not the addition of the two currents rather the only current resolved in the neutral is the result of the lower current subtracted from the higher current that cancels out the other leg.

[@RPHPros]

Thanks for this video. I have this situation where I had a 12/3 on two separate breakers that did not have a common shut off handle. The 12/3 gets split in a junction box to service two separate circuits. I am now going to rectify the fuse box issue by swapping the two separate 20amp breakers for a 20 amp breaker with one common service handle.

[@mikeiver]

Code calls for bar tied breakers for MWBC runs. Seen guys that failed to identify such, open the neutral and burn up electronics and other loads as a result. Here in the north eastern United States it is somewhat common to find. Also common are the hots both coming from the same phase and overloading the neutral. Homeowners and handyman are rather good at this one! This is also common in allot of commercial electrical installations as well. Cube sets fed with a "full boat" are a good example. Most have each breaker as a separate rather than on a 3 pole breaker. Women and their heaters take those out all the time so the maintainance worker swamps them out to prevent the whole cube set from being brought down. Ah, good times! Very good video.

[@n2rj]

Thanks for this video. This is especially pertinent because people are now getting 120/240 split phase interlocks or transfer switches installed and then using 120V generators to power them, often just bridging the two hots. So they have potential of overloading the neutral when using these generators.

[@evtguy]

This is obviously a really thorough explanation about what’s going on but I had hoped that you would explain the pros/cons of implementing this. The electrician who replaced my panel in the 2000s told me he had added 2 breakers for future expansion but this is exactly what he did- 2 breakers in the panel with a single 12-3 wire run. Many years later when I considered using this run, I finally saw what he did and was confused by it. I finally was able to learn what he had done but wasn’t why. I wish he would have just run two 12-2 wires instead of the single 12-3.

[@gregoriocampo]

Thank you for sharing your Knowledge.

[@probeteam9936]

Excellent description... I ran into this issue just the other day...

[@tedlahm5740]

Clear concise information. Suggest showing what is going on INSIDE the secondary winding of the step down transformer BEFORE showing this?

[@alfriedar5970]

Great effort explaining it…. Still slightly confused but know so much more.

[@jackl9922]

I have several of those circuits in my house. I changed out the old Federal Pacific panel for SQd ..I was careful on which pole I landed red vs black. Inspector said I should have used 240v breakers on those, but passed it anyhow since “better than before” and in the panel it’s obvious how I paired things. Later on, unrelated, had one room where lights would sometimes go bright, while dimming in another room. My guess was a dropped neutral somewhere. Found it behind a smoke detector. The wire nut came loose on the neutral. Prior homeowner didn’t do a good job when replacing the smoke detector. After finding that, changed all plugs/switches in the house and checked all jbox . No more issues! I hope people get educated from your videos.

[@jackl9922]

Ideally I should swap those breakers. Someone not knowing might turn one off and think the shared neutral is safe when working on something. I know to double check when both red and black are in the same box.

[@AaronRendahl]

@@jackl9922 can you just tie your existing breakers together, instead of replacing?

[@KevinCoop1]

You may, according to NEC buy what is called handle ties that will fit your breakers if you like. Please remember, not an overcurrent issue. It is a disconnecting both circuits on the neutral while working on something.

[@kevinvanderlei3271]

Thank you for all of the awesome videos!

[@arturotorres6437]

Mighty impressive that Dustin invested into this whiteboard or touchscreen device that greatly helps visual learners understand the concepts. It really is a shame that one of the largest community colleges in the U.S. cannot have these resources for it's instructors. Instead I had my instructor refer me to Electrician U channel. And the name of the college is Houston Community College...

[@timrxn5414]

Great video and now I know why I got a shock even after deenergizing the circuit I THOUGHT I was working on. Will fix this soon, temp solution was to take dishwasher off line and keep stove operating (gas stove so no 240v required, just igniter and clock)

[@JohnKania-jt8yr]

Awesome. Learned more practical applications here than college electrical engineering courses

[@Magicgathers]

I was like, why can’t it flow the same way? Then you answered that in the last minute. Great work 😁👍

[@xenadu02]

Our home in SF was gutted and completely redone top to bottom. They installed subpanels and all outlets and lighting (except bedroom outlets using ARC breakers) are MWB circuits. So at least some people are still installing them as of 2015, I assume to save on copper.

[@GH-oi2jf]

Here’s a complication related to that configuration which came up when I had some recent kitchen work done. I wanted the GFCI function moved to the panel and my electrician said he had to use a double breaker for the two kitchen circuits. The catch is that he wanted to put an AFCI on the circuits as well, but there is no dual function double breaker for my panel. We went with just the GFCI and the inspector passed it, so I’m happy. They weren’t new circuits, but once you touch an old circuit you are supposed to bring it to new standards. That isn’t always easy.

[@rogervancouwenberghe6685]

As a general contractor in California, I was a jack of all trades and master of none, but I did know when to be suspicious. One day on a job, a neighbor came over and asked me to look at something and I went with him because he had a pained look on his face. He showed me an extensive rewire of his house which could be viewed from his garage which was like a basement since his entire house was over his Large garage ( in San Francisco). Something was wrong with his wiring, I forget his exact complaint, but when I casualty inspected the wiring that I could see, and I found a neutral that had discolored insulation that was crispy and brittle. So with that plus his complaint, I figured it was the Dreaded Bad Neutral and I advised the poor guy to find a really good forensic electrician because the wiring appeared to be dangerous. He looked very disappointed and was already bitter about his experience with the guy who did the work. Later that day one of my electrical subs told me that really good forensic electricians are very hard to find. So so too bad for that poor homeowner. I can think of a short list of questions to ask an "electrician" before he does work on a project, to weed out the posers, but it would be impossible to educate the public about this problem of unqualified contractors.

[@gadgetguy5871]

Excellent video and explanation. The one thing I think you should mention is in situations where you have a black/red/wht cable being used on the same phase sharing the same neutral controling 2 different loads that it can be dangerous when working on one of loads. And when working on one of the individual loads that you should turn off both breakers before preceding with work. If one load or circuit is left on from either the black or red circuit still has potential from the neutral since they share the same neutral.

[@rodbalfonso5812]

Thank you for sharing your knowledge. Great videos

[@garyenos2552]

I see this all the time, and I was guilty in the beginning, using a split breaker with a 3 wire, thinking I was getting two circuits to an attic, so I learned that was a no go

[@richardfuller2326]

You need to go further with this scenario. If you lose the neutral to the cabinet that is doubled to the outlets and you have a separate load going to each outlet, then you will have 220 volts divided into each outlet, depending on their amp draw! That is why I never use this circuit unless it was a 220 circuit. I have also worked on 110 lighting circuits that shared the return circuit in which I isolated the one circuit, thinking it was safe to work on, but in fact the neutral was hot from another circuit's return.

[@richardfuller2326]

I have also run into the same situation! It was on two, 277 3-phase lighting circuits sharing a single return.

[@jameshoff9435]

14;12... We did this w/ a few lighting circuits. We had to make sure the red & black was on the same 120v side of the load ctr. The bulbs were different wattage and were sharing unintended current when needed were acting as a light dimmer to the other bulb.

[@ShredPile]

Such a good video about something you come across every so often and also end up having to do for simplicity sometimes. Tons of great extra info in the very knowledgeable comment section too. Thanks everybody!