The Dangers of Shared Neutrals: How To Avoid Being Shocked
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- Опубліковано 27 лис 2022
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In today’s age of electrical work, shared neutrals are relatively rare. Most of us run an independent neutral with our phase conductors. But can you receive an electrical shock from a shared neutral even if the breaker is in the off position? In the latest episode of Electrician U, Dustin explores this topic to bring some light to the subject.
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As discussed in previous videos, electricity travels in loops to function. On a single pole circuit (120v for example) the flow typically leaves out on the hot wire, goes thru the load, and returns to source (usually a breaker) on the neutral conductor. In addition, in most current residential work, a single dedicated cable, comprised of one hot, one neutral, and one grounding conductor, is run for each separate circuit. So, when you shut the breaker off, there isn’t a chance to receive a shock on that circuit (on the load side of the breaker anyhow) since the loop is broken.
However, in past years, shared neutrals were fairly common. A shared neutral is where you have multiple hot conductors sharing the same neutral. This was done to save wires and therefore save money. However, there are dangers present when using shared neutrals. That being, even if you turn off the breaker for the circuit you are physically going to perform work on, that neutral conductor can still have current flowing on it from the other circuit. To combat this issue the NEC now requires us to install a multipole breaker (or place handle ties on the single pole breakers of a multipole shared neutral circuit) so you are made to shut off ALL the breakers involved with a shared neutral circuit. But this provision is a fairly recent change (within the past 15 years or so) and you can still find single pole breakers for a shared neutral circuit all throughout the country.
There are a few scenarios where you could receive a shock on the neutral conductor of a shared neutral circuit. If you left the breaker on but took apart the joint on the neutral drop in the box and touched the white wire headed to the panel and either of the other 2 white wires headed to the actual device, you will just be completing the loop itself! Another way to get an even worse shock would be to leave the breaker on, take apart the neutral joint, and then touch the 2 white wires headed to the devices themselves. By doing this, you are basically completing a 240v loop and will get a wicked shock!
The easiest way to avoid all of this would be to simply turn the circuit off that you are working on. And if you are working on an older shared neutral circuit with single pole breakers, then shut them both off! This eliminates the chance of having any voltage on the neutral. Another prudent thing to do is to test if with your meter. Test your meter on a known live circuit first, then test the circuit you are attempting to work on, then retest again on the live circuit to prove that your meter is operating properly. Another thing to consider regarding receptacles. The loop is NOT complete, so current CANNOT flow, until something is plugged in somewhere in that circuit. The loop is open at the device itself. Lighting on the other hand, is connected via the lightbulb itself (or the filament within the light bulb) so current will flow as soon as you turn the breaker and the switch on! Another thing to consider, is that current does NOT care about the color of the wire! So just because you are touching a white wire, doesn’t mean you won’t get shocked if you are doing something you shouldn’t be doing with it!! Always get your journeyman’s tips or advice before attempting to work on a circuit until you fully understand the exact scenario you are up against.
We hope this has been helpful in understanding a bit how one could get shocked by touching the shared neutral conductor even if the breaker is off. Is there a topic you would like to see discussed on Electrician U? Leave a comment in the comments section and let us know. Please continue to follow Dustin and Electrician U as we are constantly updating our content to assist our followers in becoming the best electricians that they can be
#electrician #electrical #electricity #dangers #shared #neutral #shocked
Great video! Your statement that will stick with me from this day forward is "Electricity doesn't care about the color of wires".
Works for me as well... if only life was this way as well...
Love that whiteboard addition to the videos -- super helpful to see things visualized like that with the fast changes (less clunky than a real whiteboard..writing, erasing, etc...)
🤔🤔🤔🤔
They're called smartboards I had them in elementary and highschool pretty sweet!
😮😮😮
one thing I was taught when taking apart joints is to break the hots, neutrals, then the grounds; and the opposite order when putting joints together. That and keep your boots on the ground and your idle hands off of metal boxes cans or cabinets. Both are good habits to form alongside not working energized whenever possible
boots on ground?
One of the best comments.
Awesome video. I want to take this opportunitty to say thank you Dustin for this great content in your channel. I passed my Journeyman test in August 2023. I would not have done it without your videos and all the help I got along the way from knowledgeable electricians that went out of their way to make sure I understood theory and field practices. I want to learn more stuff. I am currently working at an industrial work area. I am still a bit intimidated by the environment, but the experience I am gaining keeps me motivated. I have learned that failure is apart of the learning experience. I will never let past and future failures keep me from trying my best as an electrician.
Great explanation. I came searching for why I got a shock from a neutral when the breaker for the circuit was off while installing a LED power supply in place of a light fixture. It was a shared neutral situation I found out here! Something new to watch for. Thanks for the info!
Single pole breakers are allowed on exterior lighting circuits with a shared neutral [NEC 225.7(B)]. NEC recognizes the voltage drop benefits of sharing the neutral because typically long distances are involved with exterior lighting and they recognize the liability of loosing multiple exterior lighting circuits from a single short if multipole breakers were required. So, extra heads up when working on parking lots and street lighting.
225.7(B) doesn't say anything about breakers, but it does call the multiple ungrounded conductors a "circuit" (singular), as in a multiwire branch circuit. 225.7(A) says outdoor lighting circuits shall comply with 210; including the handle tie requirement for MWBCs. Something of a moot point now since 226.7 has been deleted in the 2023 NEC; it was an unnecessary section IMO. But yes an extra heads up when working in those locations; a common danger is the lack of EGC.
@@barryomahony4983 You're right...2023 NEC has deleted the exception that permitted the shared neutral for exterior lighting. There are many municipal lighting systems that use the shared neutral...It allows street lights and the seasonal lighting receptacles on the poles to run at 120V, and have each pole stagger circuits so if there is a fault, only half the lights would go out, which is much less dangerous for drivers and pedestrians. Now without the shared neutral, the conductors will go from #6's to #2's and have to run an extra neutral. And there will be current on all the neutrals, wasting energy (about 1.5% wasted energy - not much but still less efficient). I disagree with the NFPA - there are many good reasons for that exception for exterior lighting in the code.
Its not just exterior lighting but where you have sensitive equip. like a lab, just removing the neutral could fry whats on those circuits, even cutting circuits off not together can also do it.
@@danhardhat2 Well, I'll have to reread this but I didn't think it prohibited these shared neutral circuits. These are completely safe circuits and quite useful and practical for long runs. Not very common in regular residential wiring. These used to be quite common in long agricultural buildings and shops. As you point out, there are applications of this that make a lot of sense.
I tend to look at it this way, what properly trained electricians would think it OK to spilt a two pole breaker into single pole circuits??? I can kinda see a DIY homeowner not understanding, but then I have long advised against electrical work as a DIY skill. I blame the internet for convincing people that they know what they are doing, when they clearly don't. What makes it even worse is all the stuff posted from 240 volt countries like "this is how it works everywhere in the world"!!!! It just confuses the hell out of DIYers. wh really should not be doing this work in the first place!!
Does anyone in their right mind consider DIY surgery?? IDK, but I'm guessing that most people realize that the consequences of not completely understanding or doing something wrong, might be fatal. But working on electrical without fully knowing what you are doing, can have the same kind of fatal consequences.
I know of a journeyman that became the neutral on a 277 volt lighting circuit, it knocked him off a 12 ft. ladder and fried his brain.
Great thing for me to learn about ,we just did a panel upgrade for a customer and the inspector wanted me to “handle tie” all ckt breakers that share a neutral and zip tie the neutral wires together to ID them
Exactly. Breaker handle ties 👍
Yes Multi wire branch circuits , and don't zip tie them. Tape them at the panel all together with an identifying tape color if you have several similar circuits , make your inspector happy 😊
The most basic question that I wish the video spoke to is, how do you know if there's a shared neutral? Inside my panel I saw red wires used for 120 v circuits. That caused me to trace where the wire was going, which was Romex that also had a black conductor from another circuit. I hadn't seen this before and ended up learning more about it on your channel. IMO it's crazy that shared neutral circuits are allowed in residential construction because over the life of a home, someone can easily rearrange things in the panel in a way that's unsafe. In one of my circuits, someone had put the red and black wires on the same phase and ended up with double current on the neutral, which was a fire hazard and had to be fixed. Our home inspection missed this issue.
Not an electrician, so take this answer with a grain of salt, but the only way to somewhat know for sure is to open the panel and trace the wire for the circuit that you're working on to see if it's something like a 14/3 or 12/3 (and then double check that they're on different phases like they should be). Even then, you have no guarantees that someone didn't do something insane like tie neutrals together from different circuits if there are multiple circuits in a junction box. If you didn't wire it yourself (meaning you're not 100% positive how everything is wired), just take the 30 seconds to put your meter on each wire to see if there's voltage.
Btw just because the wire is red doesn't necessarily mean anything at all - 14/2/2 or 12/2/2 is a thing, so a single piece of romex could have enough conductors in it for 2 full circuits with no shared neutrals, but there may still be a red wire present there.
Usually 2/2 wires they indicate with a red mark on the neutral with the red and black mark on the neutral with black
I've got a degree in electrical engineering so maybe I can help.
You won't know! Also, it's not going to be an issue unless you mess with the point where the neutrals are tied together or in the circuit breaker panel if the other breaker is still on!
Best advice from someone who have 30 years experience, just turn the entire circuit breaker panel off if your not sure about how things are wired. You could also use a tone generator to see if the neutrals are shared.
Fluke Pro Probe 3000 toner, there are videos on UA-cam how to use this tool 😉
Home inspectors aren’t usually electrical professionals. It’s not their job to get in to the nitty gritty of the panel.
You can melt that neutral wire like a candle if both positive wires are landed on the same phase. If they are loaded up double the amount of current is returning back on that neutral. The breakers won’t trip but that neutral will fail spectacularly. Maybe a video should be done on this because it is easy to make this mistake. Keep up the great work !!
He's got that nice "teaching wall" that has demo outlets and panels, so he could use that. I say New Years is a great time to light that firecracker!
Positives huh.
@jasoniron6664, I think you need to stop watching youtube video’s, and go to a proper schooling, to learn the difference between ALTERNATING & DIRECT CURRENT applications.
Hot, not positive.
Also, it's actually difficult to make that mistake because a 2 pole breaker connects to adjacent bus bar tabs that alternate phases. So unless you go against code and use 2 separate nonlinked breakers and install them with a gap in between them or an odd number gap in between them and land on the same phase, this problem wouldn't happen.
@@ReeceMayer Enter home owner re-arranging the breakers in the panel, so they are in a more logical order. "Why are these two kitchen breakers linked together? That's dumb. I think the breaker for the microwave belongs between these two."
One other thing happened when I was having my business rewired in an old 1937 commercial building with one, two or three businesses being housed in it over the life of the building. The electrical panels and wiring had been changed and upgraded (sometimes by amateurs) several times. The landlord had a supposed electrician come in and change the timer for the signs from one business in the building to another but the conduit to the sign was still in the first business location. The pseudo electrician took his power from the other business main panel but somehow left the connection of the neutral on the first business main panel, so there was a hot wire from one panel and the white wire from another main panel. So my commercial electrician who was installing whole new panel for my business shut all power off to my panel at meter. As he was pulling the main leads the hair went up on his arm near the neutral and he stopped immediately. The back feed was quite significant. Traced it to that old timer box. I think it was a once in his 15 year experience happening. Still when all power to the business is shut off and supposedly we all had our own meters, and main panels, i can see the mistake would be easier. But you have said always check for current even in a dead box. Jerry. PS Love your channel. Have watched most of your videos
Super good video. It is good to instruct the helpers/apprentices to be very careful in old houses and make it a requirement to turn everything off at the main before working on any circuit where the neutrals will be broken apart. One for safety and two to keep from blowing random things in the house up from open neutrals. Bought an older house and discovered that every single 120v circuit in the house were ran in a loop of conduit (from and back to panel) with a junction box every 10'. The circuits had 4 neutrals total from the panel and every neutral was half ass twisted together as no wirenut would fit with a piece of tape for cover at every junction box. Honestly don't know why the house had not burned down.
Back when I first started as an electrician, we ran a 12/3 for two circuits. But in the panel, we installed a two pole breaker. So that when you had to work on that circuit, you could do it safely. Now they make 12/2/2 makes it easier to deal with.
Genius. Clear and concise description. You’re and excellent teacher.
We installed multi-wire branch circuits on the west coast well into the 2000's. Once arc faults started being required in more areas is when we moved away from it.
So expect to see it in houses up to 2008+.
I went to work for the state (TX) recently and it’s pretty common for the electrical contractors to share neutrals on new installations. I’m a maintenance electrician and I’m getting pretty frustrated with the crap they leave behind for us to deal with. There’s shared neutrals everywhere and an “anything goes” color code. In Austin it’s red, black, blue for low voltage and brown, yellow, purple for high voltage. But within Austin’s jurisdiction State jobs are not subject to AHJ. So some contractors do it by Austin code and others do it by everywhere else color code.
up here in new england i see this all the time with older homes....nothing is ever labeled in the panel of course..
The shared neutrals on new installations being allowed is on the inspector for passing it. It isn't code.
First off, thanks dustin for making these videos. Extremely helpful. In addition to what you explained, it should be noted that a multi branch circuit(shared neutral) should be on separate phases. Never coming from the same phase! Keep on spreading the good word my fellow sparky.
Love your videos! I have been a draftsman (drawing) all my life, not by profession, but a drive. I love drawing day. I always work stuff out by drawing. The way you explain things and visually show it is Awsome. I have had so many AH.HA moments this way. Thank you so much, keep rocking it! God Bless.
Working on an old house with shared neutrals (and buried boxes) right now and it’s driving me bonkers. Thank you for the reminder to make sure I’m being safe with this stuff. Old greenfield cable is always waiting to bite you at every turn.
Several years ago I built a post and beam garage. I intended on doing a little woodworking and other projects. I was very busy and couldn’t find the time to wire it myself. I hired a seasoned electrician with a great reputation. I had already set the sub panel and pulled the cables. I explained that I wanted 3/4” conduit with metal boxes and GFCI receptacle on each circuit. I came home and found that he used 1/2” conduit and shared the commons and grounds and had not installed the GFCIs. I called him and he said, “The GFCIs were not necessary and that he was able to pull all the wires through the 1/2” conduit. I paid him and a few weeks later installed the GFCIs which wouldn’t work. After asking an electrical engineer, I found out that a GFCI meters between the neutral and the hot wires not the hot and ground. They shouldn’t be wired using a shared neutral.
GFCI calculates the energy going in (hot) and going out (neutral), if the difference between hot and neutral is big (someone turned into Earth and got zapped) then it will automatically trip itself preventing further damage. It does not care at all if Neutral is shared or not, but bear in mind that after Neutral and Hot exits the GFCI, you can’t connect equipments before the GFCI Neutral and after GFCI Hot or there will be imbalance and it will trip. The simple fix is to put a neutral bar connector after/before the GFCI, that way if you need to put an outside circuit that won’t be affected by the GFCI (like a light circuit, to easily find the GFCI after it trips and then reset it), then you’ll be able to wire the light breaker before the GFCI and finish it with the Neutral before the GFCI.
I'm not an electrician, but I have done some electrical work, because my state is pretty lenient with that stuff. However, my rule when I fool with anything electrical is to shut off as far back as I can without it being a problem. For example, I had to change my dryer plug awhile back, I flipped the breaker labeled "dryer" and I tested the plug, and it still said 120 volts. Someone had something wired wrong, and I didn't know where the other line for the dryer was, and I still don't know what the second line on the dryer breaker went to, so I just had to kill the whole house, just to change one receptacle. That's the fun of living in a 30 year old house trailer, that God knows who has lived in before you.
I appreciate this video so much, with how we do wiring currently most apprentices never learn how or why this was done. In my area there was a housing boom when the wiring was like this and I encounter it frequently and use the opportunity to teach it but now we have a great illustrated video!
I know this is late brother but I know of a fellow electrician that past because of this very situation. South east texas last year. Please be careful out there brothers.
What an awesome dude! Passing out life saving information like it ain't no thing! Respect for that! And in a concise and captivating manner. Thank you!
Job. Well. Done!
Gotta love multiwire-branch circuits in old 3 phase building.
Oh yeah! With breakers that aren't right next to each other. We just hope they're on separate phases... And don't even get me started on junction boxes with not only multiple circuits, but from multiple panels that are halfway across the building from one another. Got my exercise that day!😑
I always wondered why, when doing panel swaps, we had to put three wire homeruns on a 2P breaker… that makes a lot of sense now!! Thanks man!
Fantastic coverage of this topic, thanks!
When you're dealing with wiring of questionable installation quality something I started doing was to use a clamp on current ammeter or current probe whenever I came across commoned up neutral wires (such as multiple white wires in a wire nut) to solve the mystery . Before removing the wire nut and separating these mystery neutrals check each wire with the clamp on ammeter for presence or absence of current . If there is different current reads on each neutral wire you can compare the load current going out from each breaker and when you have a match mark the neutral wire with that breaker number then turn off the load breaker and verify both line and neutral reads go to zero amps . If two circuits both read the same current value add more load to one circuit to make them easy to distinguish between the two circuits.
Dustin's videos are always exciting to watch.
Thanks for great info. Always appreciate your advice.
Great explanation, as usual!
I ran a new 2-pole 20A breaker with 12/3 dedicated line for my shop table saw, splitting the duplex 5-20R receptacle into 2x 120V 20A with the shared neutral. It is so I can upgrade it down the road to a 220V 20A simplex 6-20R receptacle when I upgrade my table saw from 120V to 220V. In the mean time, it provides the saw's 120V and an extra outlet for some lights until then. The key thing is it all ties back to that 2-pole breaker so both "legs" are shut off and never just the one. Hopefully this meets code... chime in if not please!
I'm planning on doing this in my shop as well... I'm not sure why if it was on a double pole breaker that it would be a problem
I saw this on one of your best of videos and it was eye opening! Not allowed where I live but I see them in places I do work. Never considered overload of the neutral if both power wires are on the same bus.
Awesome video! I'm relatively new to the channel, so it's awesome seeing this, as I hadn't ever thought about something like this happening, let alone know that any older house wiring would share a neutral. Does reinforce the importance if sticking a non contact voltage tester around all wiring to be worked on before toughing, though!
Not only have I gotten bitten by a neutral, when I was a teenager I got shocked off an electric water heater. Changing out an element. Uncle Gary turns off the breaker and tells me it's off. Of course I verified the power was off with a multimeter that I tested on a known live circuit. I tested across the terminals on the upper thermostat, but didn't think to check each leg to ground. What happened was there were two single pole 30s in the panel which has been there since probably the 50s or 60s. If memory serves me right the two 30 amp breakers were not even near each other, just randomly placed. Talk about some shady work.
You are awesome man. Keep up doing what you do. Always feel appreciated. From Kenya.
Super clear explanation! Thanks!
Really nice explanation as always Dustin 🤠
40 years ago, the Contractor I worked for used lots of Edison circuits in new homes we wired. Another electrician I worked with told me of this very situation where he got shocked touching a neutral wire.
Great information and tips!!!
One potential way you can get shocked from a neutral is if the breaker is off but there is a device with a large capacitor connected then it could energize the circuit
Lol. I shouldn't laugh, but somehow it just seems funny. Capacitor's 101: Q: How to discharge when the neutral is cut. A: Insert random electrician for path to ground. :)
Aka multi wire branch circuit? I have some of these in my 70's home. It really threw me off as to why I had 240v circuits feeding 120 volt devices until a friend explained it to me. Excellent video as always. Thx
3:26 You could still get a mild shock from the upper white conductor if you touch it while grounded; a small portion of the return current will flow through you.
Good point. But I'd say "could" not "will." While many things are fairly straight-forward, this would be complicated. Depends on a lot of factors, like how "grounded" are you and possibly where you are along the circuit path. Not to minimize the danger; I sure as hell wouldn't touch it.
Absolutely! If your body is providing the path to ground, then that "stub" white will all-of-a-sudden have current in it.
Reminds me of switch loops and the measures electricians used in the 80’s to combine wires to save a few feet. Navigating the branches in a home from this era is a mess - fortunately they didn’t play the shared neural game in my house.
On a side note - one example of a shared neutral application today would be to a main lug sub-panel.
Hey man, love the videos. Keep it up. What Code section covers the handle tied breaker?
Thank you just what l needed!
I still see shared neutrals being used in new contruction for Dishwasher and Garbage disposal receptacle all the time out here in Az.
I did not find in the NEC anything about those breaker needing to be tie together but it totally makes sense so Im going to start doing it. Thank you foe the awesome presentation
Awesome video. I am an HVAC Service tech by trade and trying to learn more about non HVAC electrical so this is very helpful
Great explanation!!
Yes I’ve gotten a poke before 3 phase 347v because the wire nut was not on the wires properly. It came from the neutral. Hurts like an sob
Glad to see this issue is being addressed. I am in a 30's house where wiring is all in conduit. Everywhere they could, shared neutrals were used. When I added some circuits years ago, I just assumed this was standard practice, followed it and did not fix them. But somehow it just did not feel right. This was long before the days of the internet, UA-cam and all the learning resources now available. I did go back and check the circuits. I actually made and kept detailed diagrams of the wiring because of how they mushed so many wires together in a single conduit run. They all seem to be on different phases. If I ever need to do more, I will run separate neutrals.
I guess at least there was conduit. it was probably considered to be an excellent installation when it was done lol.
I'm assuming it's BX flexible conduit. My and my parents' house (in different cities but both in the northeast) are from the '20s and both have that. Agree if everything is on opposing phases it should be totally fine from a load perspective, but that old BX should be replaced eventually.
A one-bedroom apartment was divided and converted into two studio units. I am unit A and my neighbor is unit B. We both have been living in the property for 4 years. A couple of months ago unit B has been having trouble with his outlets. Which affects my bathroom lights. Landlord refuses to fix the problem. And Unit B refuses to get extension cords and fix the problem as well. I am being forced to either give unit B a key to my unit in case I'm not home to access the circuit breaker. Or landlord threatened to evict both of us, if we don't work together in regards to this issue 🤷
Report him.
I love your content and really appreciate the work that you do. Having said that, I'm always a little confused about why it would matter whether the powers turned off or not. If PPE has been uand proper procedures be used, it doesn't generally matter. I will readily admit that there are times when I will absolutely turn power off, for instance when there's a mechanical device like a condenser fan replacemeant, or I'm pulling a motor, We're working on sense of electronics that I need to unplug and I need to protect. But the usefulness of having the power live, particularly when doing diagnostics, really can't be overstated. And yeah, you get shocked when you first learning how to do this,. But if you can survive the apprenticeship, you learn not to get shocked. Having said that I've been bitten by 120, 208, and 277. Those last 2 are not fun, but also not something that happens more than once.
Excellent explanation of the shared neutral. As a lighting designer, we could share a neutral with each of three phases when laying out a large system like an office corridor. It was easy to balance the loads, they were all the same fixtures with the same lamps, and it did save a ton of wire in these big spaces.
Thanks! My son told me about shared neutrals when I attempted to remove some aluminum wire in a panel that didn't seem to be doing anything. He said sometimes electricians use neutrals to save on wire and best left alone until the circuits can be checked fully. Panel is circa late 80's
When I started in the trade in the late 70's the old timer I worked with had a cheat for dealing with mwbc to avoid the live neutral. He would locate the circuit to be worked on, shut it AND the breakers above and below it off as well. Which will work.....unless the two hots were not landed properly.
He got caught a few times by that last bit.
Very helpful Thank you
Those "You can't be shocked by a neutral" people aren't going to like this one either LOL
Open group and loose neutral hurt more than the hot lol
@@thewiseguy390 why
@@thewiseguy390 I can confirm this and it does hurt like hell.
Confirmed..it hurt.
Only a dummy is a the reason for someone being shocked by a neutral wire bc a neutral being wired improperly would cause that to happen. Which would be due to a dummy improperly wiring the neutral. A properly wired neutral cannot shock you.
Great vid!
I always anticipate that something won’t be correctly done. Just found multi wire branch circuits run from a quad-breaker with the ever popular handle tie delete option. Eaton quad handle ties fit nicely on Murray quads. I always expect Neutrals to go live when unbuttoned until I check them with my chicken-stick post disconnect. I think Uncle Fester used a lost panel neutral to energize his light bulb.
"Now you have a 240V shock on your hands" classic!...loved the video thanks
Sawmill tech here. You should cover ground loop when dealing with a short to one side of a "space saver". I had a light switch cover plate that had 110v to ground after removing it from jbox. And the switch was. In good working order.
Other danger i see is if on and remove the main neutral then you have 240V like you said but also may end up with the loads being wired in series. Series in theory each would get 120V but it would depend on the current draw of those devices. The larger draw would pull more voltage but could also fry the other device due to drawing too much current through it.
This is also why when I work on even dead circuits I splice things in this order Ground, neutral, hot. That way you are really only exposing yourself to the hot potential once as oposed to splice the hot then the neutral. Ground first just should there be issue and sometimes for small fixtures it is a nice anchor point to hold it till you can get the other wires linked.
Your basic logic is sound, but I think you’re confusing voltage and current. The larger draw would get less voltage. If you run a 60 watt bulb and a 100 watt bulb in series across 240 volts, the 60 watt bulb will see 150 volts and the 100 watt bulb will see 90 volts. (Ohms law).
This explains some unexpected shocks that I have had! Ouch!
I had a 200 amp panel installed and noticed there many joined cicuit breakers. Asked the electrician about it, and he said our state (CA) now requires that setup. When I asked about troubleshooting just one circuit breaker, he said go ahead and pull the tie off.
Recently had a situation that they had run 12/2 and tied the neutrals together in another switch box. We we’re replacing a bathroom outlet with a GFCI ( place was built in the early 70’s ). Couldn’t get the GFI to set. I had to start running down the wires in the other places that the power went out with that breaker. Found the neutrals tied together in a switch box.
A secondary path can also be from Satellite or Cable service as the coax cable is directly bonded to the ground outside which can be an alternate path that can get you if there is any bleed through on the power packs or the devices themselves. If you ever have a customer tell you the Cable guy asked if their lights flicker or point out the coax is melting you have a potential open neutral or a bad connection in a box where someone was able to get 5 wires in a 3 wire wire nut or something similar the coax used should have no voltage when measuring from neutral or ground at the outlet to the metal connector of the cable jack, coax is also not rated to carry current but will until it cant anymore.
Great video 👍. One thing that I keep finding in older homes I'm called to with shared neutrals. The neutrals shared with the red and black on the (same phase) which- could cause overheating/over current carrying conditions on the neutral wire.
i think that would keep the potential for 240v down.....still notta good idea
In theory the phase is alternating so electricity flows in equal opposite times down the wire not doubling up, sometimes getting out of balance but the idea is they don’t heat the neutral more than the hot because of alternating current and also the load supplied has slightly less current coming back
@@JPLaJeunesse I agree with most of what you said. But for the neutral carrying alternating current from shared red and black Has to be on separate/different phases for the neutral to carry the unbalanced load so as it won't overheat. Would be good video content as an experiment to prove this theory 🤔
Your a good teacher man honestly 👌. Never cared about electricity but I’m more interested now and wow it’s a lot to it especially in old houses when changin outlets it’s hard to tell if there shared neutrals off separate breakers as a lot of code is different now 😤
Awesome content. Thankyou sir
It's a significant savings when you are doing a big job. In Chicago We can put 9 wires in a conduit, that would be (6) 3 wire circuits or only (4) 2 wire Circuits. We use a 2 pole breaker and use a wire tie to bind the three wire circuit together where it enters the panel. When connecting power poles in office cubicles and outlet buss ways, they are all wired from the manufactures with 3 wire circuits, so they are a necessary evil. If you have a lot of expensive electronic equipment, 2 wire circuits are best practice.
@7:45 So this is actually a really common misconception. If you are using two 1 pole breakers with a handle tie that does not mean they are common trip. What makes a breaker common trip is actually an internal mechanism on factory 2 pole breakers with the common trip feature. If we have a 1 pole 15A circuit for example and I hold the breaker closed and someone shorts it downstream it will still trip and kill the circuit even though it's being held closed, hence trip-free breakers. We can actually see this in the UL 489 certification with the following:
Independent Trip - A 2-pole circuit breaker that does not have an internal common trip feature is marked “Independent Trip” or “No Common Trip.” An external handle tie alone does not qualify as a common trip mechanism - a breaker of this type is marked to indicate it is an independent trip breaker.
The main point of the handle tie with multiwire Branch Circuits is to make it so if someone actually moves the handle both circuits will open/close together. It's also to make it so that if some other electrician shows up who didn't do the original work, they see the handle tie and look and know it's a multiwire circuit and to be careful. If we have two 1 pole breakers in good condition there is a good chance, they still will trip but it's not guaranteed and if the breakers are older and stiffer, they probably won't trip.
If you read 210.4 (B) (B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.
Doesn't actually mention anything about the trip.
I wire hospitals, colleges, large commercial buildings. If I get pulled into helping a friend wire a house, I eat the cost, or make him eat the cost, of running a separate 12-2 for kitchen receptacles so no 3-wire circuits are in the building. For residential where the finished product is unsupervised it makes no sense to leave a 3-wire circuit for the homeowner to play with. They usually put both red and black on a tandem when they run out of space in the panel and double the neutral current.
Thank you for this video. We are actually having to do this in some apartment buildings right now (they want all plugs on their own breaker, and it is in the blueprint to run them like this). Great info to k ow before we turn the power on.
Shared Neutral shocks are the worst! Thanks for the video!
Well now i have to go up to my fishing cabin and install a tied pair of breakers. Thanks, learn something new every vid.
Hey I think your videos are great for beginners and I think you have a great way for normal people to understand things, I’m hope you could help clarify some more about two hots one neutral, because of the video about running cross overs from 120 volt generators, to a panel . So I’m wandering about wouldn’t that be same as adding the Amps of all the loads the generator pushes and would it double the amps on the neutral back to the generator,
Any thoughts would be helpful and thanks
yea we ran 12 /3/4 until very recently. on home runs we would pull three phases one neutral one ground. saved alot of room in the conduit, ment more circuits in a smaller pipe.
Hey Justin: hope all is well with you!
The 1930’s house I live in has had the wiring updated in the past (20 years or so before I moved in) and while in the process of connecting a new shop light to an existing J-box, I noticed the circuits within it have been wired via shared neutrals, which aren't labeled (numbered) to partner them up with their corresponding hots. Do you have any suggestions that I can use to trace the white (neutrals) to partner them up with their respective black (hot) wires without having to demo the plaster walls to locate them physically? In other words, is there some kind if an instrument that I can use to detect them.
I’d appreciate any feedback you can provide.
Best regards,
Joe
Thank you 👌 my 1940’s bungalow I keep finding tricky electrical issues with. Spilts tapped up in the walls and in the attic entirely without junction boxes. Then when the time came and the old fuse panel was replaced with circuit breakers. They threw some new wires at it and walked away. I’m stripping the attic out to air seal and insulate. I’m installing new low voltage LED lighting while I’m up there.
LOVE your information!! LOVE your insight. Thank you for all that you do.
Since the 1960's, I have been repairing vacuum tube electronics. The very main thing to do is to isolate the hot to common by replacing the "death caps" and installing a polarized plug. I like the 2 prong that only fit pole outlets. I get many comments that I am wrong by not using 3-prong, however, I do not want to ground the common at the outlet. Am I wrong? Should I be better by using a 3 and leave the ground prong open? Is the 2-prong polarized still the best in your opinion? (I'm sure that the common is energized regardless of what plug is used, anyway).
THANK you MUCH!!
Especially on a resi shared lighting circuit!
I wired my workshop using shared natural so that I could have two circuits in every junction box (I used different colored outlets for each circuit) so I could balance my draw when using two tools at once (ie a saw and dust collection) and it was easier to pull a 12/3 wire vs 2 12/2 wires.... but I labeled both circuits in the box as a shared natural and tied the two breakers together with a bar.
Thats good to know. Just bought a house with older wiring and I tend to work basic repairs or replacements live. But never again until I make sure its 💯 safe.
I have a situation where I would like to rewire a light fixture to be on the same circuit as some other lights that are on a 3-way switch. I have easy access to the switched hot and two travelers on the 3-way switch, but no easy access to the neutral for this circuit. However, I do have easy access to a neutral on another circuit in the same switchbox. It is tempting to just use the neutral from the other circuit, but I know this is not safe for others who may be working on this in the future. I was considering using a current sensing relay to move control of the light fixture to the circuit with the 3-way switch, and still powering the new light fixture from the circuit I have a hot and neutral for in the box. Any suggestions? I would like to avoid tearing into the wall just to run a neutral to the switchbox.
Once I went to work on just a simple light. Rather than going through the trouble of finding the breaker in an unmarked box I thought I would just turn off the light switch and I'd be safe. But nope, I got bit with a fairly strong sting, but not a full load that I would expect from 120. After watching this, I'm guessing that it was some sort of a feedback through neutral from another device on the line/circuit that was turned on. Very interesting. (always trip the breaker!)
Important to think about during ballast replacements in 277V applications in large rooms with rows of lighting fed by multiple circuits. I'm sure there's nothing like having a hot neutral fall off of the fixture your working on into your ear or eye while standing on a ladder.
277 is a bit harsh for beginners. Start 'em off with a 120V lighting circuit with the switch on the neutral side, then leave them unattended while the old "I turned off the switch do I really need to turn off the breaker too?" argument plays out in their heads.
Thank you for your knowledge and video's USA 🇺🇸
In cases of a shared neutral it should be connected to a load with a pigtail so that if the load is to be disconnected the neutral connection isn't being opened. Some of the older buildings I work in have 120/208 3ph panels with 3phases sharing the same neutral, I see it all the time non pigtailed neutrals at receptials and lighting ccts it can be a challenge to determine which 3 ccts are involved.
Great Videos! I have a Question!!!
How would the scenario below effect the True Neutral going back to the Panel box???
I'm a carpenter, not an electrician but I have working knowledge of electricity. On a bathroom remodel I was taking down two can lights from the ceiling that operated on one switch that were going to be relocated in the same room. 12-2 (power from the breaker box) was coming into the light box in the ceiling. He ran one 12-2 wire to the switch in the wall to send power to and from the switch back to the light. So, in the light box I had a white wire that was actually a black wire(power), and it was tied into the black wire that ran over to the other light for its power source. Usually when I see this the electrician has always put black tape on the white wire coming into the box from the switch so you would know it was being used as a black(hot), but he did not in this case. So, looking in the light box in the ceiling you would see two blacks together, two whites together and a black and white together.
Most commercial projects my employer had us run one neutral per 3 conductors on a three-phase panel.
All of these loads were calculated and balanced of first to the best of our ability
Nice video, As an EE, with 30 years experience, I see nothing wrong. with your explanation.
Recall as a rookie engineer, we were dong an upgrade to an OEM machine. they had 2 different breaker in a panel, not even close to each other feeding a 240VAC load. I was like really, we had to call in Electrician to re-wire the box to fix this. They were pissed of at new rookie, but I had to raise a stink to have it done right.
Excellent video! I am constantly telling guys that electricity doesnt care about the color of the wire..... You have to understand its path not its color.
Another thing to mention would be the situation where the home run neutral to the panel is lost and now the shared neutral spice becomes a bridge between two different phases resulting in different voltages across the circuits depending on how much load is applied to each circuit.
Let's say L1 through a 50 watt bulb, through a bridged neutral with a lost home run (no connection to the neutral bar), through a 100 watt bulb to L2.
The 50 watt bulb will be running on more than 120 volts and the 100 watt bulb will be running on less than 120 volts.
The 100 watt bulb would be dim and the 50 watt bulb would most likely burn out rapidly.
The voltage potential imbalance obviously being greater or lesser depending on the difference in total resistance of each circuit. Now imagine sensitive electronics running on either of those circuits.
As a retired Lineman/cableman of 37 years, those in the electrical trades really need to realize how critical important the neutral and grounds conductors are. Yes, they are conductors and need to be treated as one.
My house has that type of wiring. The cool thing is they soldered all multiple wires then taped no wire nuts, 1941 vintage. Nice video.
It’s pretty wild to hear Dustin mention my name. I’ve been watching the channel since I first got into the electrical trade and it’s been a huge help. I appreciate you sharing your knowledge and experience with the rest of us. Thanks!
The only thing though is your comment needs to say "bruh" and is missing a 🤙
"Electricity doesn't care about the color of wires" - I learned about this the hard way many years ago when trying to discern where wires went so I could replace/update old wiring (I'm not an electrician at all, just a guy doing thing I kind of know about for family and such). I had ASSUMED that the person who had wired it all together had followed the "rules" but this simply was not the case. They had switched between black and white wires from one outlet to the next and so sometimes the black was hot, sometimes it was neutral and so on. I know there are times we need to troubleshoot with the power on in order to locate the source of an issue, but once you're pretty sure you know that information, just turn the damn breaker off.
Thanks D.
Thanks! This is an awesome heads up as I've never thought of that and am a novice to home electrical work.
I have a very strange situation that led me to this video and in short, I have a 220v breaker turning on a 110v circuit (bathroom, etc.) and what looks like power fluctuations in some of the outlets & the oven. My uncle mentioned I have a "floating" neutral I need to find. He said that the neutral and ground wires are not supposed to connect/be shared anywhere except back at the sub-panel (I think) and his believes this is the source of the strange stuff I'm seeing and/or a neutral is being "borrowed" from another circuit. There was one of the main 100 amp fuses coming in from the street but he's saying that's not why I'm seeing the power fluctuations.
A video about why you can't share a ground with neutrals would be great since that doesn't make sense to me why electrically it wouldn't work. It sounds like from this video it should work but it's just dangerous to work on live (not that I'd do that)?
He's telling me I need to test each outlet/circuit to find the issue. I'm guessing I need to disconnect each and every neutral at the bus bar in the subpanel, then I can test for continuity between the grounds and neutrals at each switch/outlet to see where they are wrongly connected?
The neutral and ground must be bonded together once and only once at the point of first disconnect. If they are bonded together somewhere else, between that point and the first bond, the parallel paths cause current to flow on both the neutral AND the ground conductor in inverse proportion to the resistance of the conductor. (Just learned this myself while hooking up a portable generator to my main panel via breaker and interlock)
Thank you for making this video. This will absolutely keep people from getting electrocuted.
Yes we did mostly built 90 has share neutral at kitchen disposal and dishwasher so after we demo the kitchen. What we did is to make the breaker to be one pole with tanden has clip together with if the disposal trip they trip same time. Hoping mostly home owner got some tip between the share nuetral.