NOT SAFE? Losing a Neutral in a Multi-Branch Circuit
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- Опубліковано 7 чер 2024
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Have you ever wondered what would happen if you removed the neutral wire on a multiwire branch circuit? Would it be as simple as your toaster not working or would it be something much worse? In today’s episode of Electrician U, Dustin explains what would happen if you did.
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In a normal 120v branch circuit, I think we all know what would happen if we removed the neutral from the circuit. Since current flow needs a complete path from source, through the load, and back to source, the circuit would NOT function if the neutral was removed. It’s also helpful to understand that the neutral conductor carries the full load of the circuit in a normal branch circuit.
On a multiwire branch circuit things are very different. A multiwire branch circuit is where you have multiple phase (hot) conductors that share a common neutral. The neutral conductor carries only the unbalanced load between the 2 loads. There are rare cases where the 2 circuits are drawing the EXACT same amperage and the neutral conductor has ZERO load on it, but again usually NOT the case. If you were to remove the neutral conductor on a completely balanced set of devices in a multiwire branch circuit, you are in essence adding the loads together in series. Yes you have double the voltage, but keep in mind that you have double the resistance working against it. Actually, things would function as normal.
But if the loads were unbalanced (as they almost always are) things could get ugly! Let’s say we had an 1800w toaster on one 120v circuit (1800w, 15a, 120v) and a 600w TV on the other (600w, 5a, 120v). The neutral conductor carries the unbalanced load between the two, so it would carry 10a and everything functions normally. If you were to take that neutral away, you would in essence have a complete 240v circuit with 2 different sets of loads in series. The resistances would need to be added together (as is the case in series circuits) which for our example would wind up being 32 ohms. Dividing the voltage (240v) by the 32 ohms we would end up with 7.5 amps (and in series circuits, amperage is equal among the loads). Again, it is helpful to understand that in series circuits, amperages are added together to make up the total amperage of the circuit (for our case it is 240v with the neutral removed).
So, taking the 7.5 amps and applying the INDIVIDUAL resistance to the equation, we can start to see how damaging removing the neutral would be. Our 1800w toaster now is operating on 60 volts (7.5 x 8 ohms of resistance) and our 600w TV is operating on 180 volts (7.5 x 24 ohms of resistance). The toaster is not receiving the proper voltage to generate the 1800 watts of heat so it would not get very hot and is under performing. BUT, the TV is operating at much higher voltage than it is designed for and will most likely be damaged as the circuit boards would probably fry, things may melt, etc. Using the power wheel equations we can finish painting the picture of what our equipment is actually doing. Our 1800w toaster is now consuming less than a third of what its supposed to at 450w (60v squared divided by 8 ohms of resistance) and our 600w TV is consuming more than double of what it is designed to at 1350w (180v squared divided by 24 ohms of resistance). While the toaster is not suffering quite as much damage as our TV (again, the toaster will not get hot and may not last as long as it’s struggling to produce the heat without enough resources to do so), the TV will burn up quickly as it’s being pushed entirely too hard!
We hope this has been helpful in understanding the loss of the neutral conductor on a multiwire branch circuit. Is there a topic you would like to see discussed on Electrician U? Leave us a comment in the comments section and let us know. Please continue to follow Dustin Stelzer 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 #not #safe #losing #a #neutral #in #multi #branch #circuit
![Branch Circuit, Multiwire, NEC 2020 - [210.4], (19min:38sec)](http://i.ytimg.com/vi/Qynp92rIlYg/mqdefault.jpg)
When I was an apprentice working in a 120/208V 3ø panelboard in a retail store, one of the first things I learned was NEVER lift a neutral until I'm absolutely certain all the ungrounded conductors associated with that circuit are de-energized and never assume that a two or three pole breaker or single pole breakers with identified handle ties has been used. I also like to use a clamp on ammeter on the neutral as an added precaution to make sure no current is flowing after turning off the breaker. You never know if the codes weren't followed and a circuit from a different panelboard is sharing that neutral.
"Why is that neutral wire insulation brown/black?"
Oh, some DA shared it. Wipe off the crinkle coat and toss some tape on it.
@@JasonW. yep that'll happen if two hots on the same phase are sharing a neutral, in this case the current in the neutral will be additive instead of canceling out. An overloaded neutral would not be possible if a two pole breaker or single poles with identified handle ties are used as required by Code. That's why I keep my clamp on multimeter in my tool pouch at all times while in the field. Test and verify, cannot be stressed enough.
Thats exactly why neutrals are so dangerous. You cant always measure them but you can still get shocked. Which is why videos like this are so dangerous.
my 2nd or 3red pair of milly walk yee 6 in 1 stripper cutter things has extra stripper slots/holes in the cutting shears because of that silliness, ... that and coming back from lunch without RE checking LOTO... SFMF
Brilliant! Always been a fan of the math. I've always avoided a shared neutral because of unintended consequences. Running a separate circuit is way cheaper than an insurance claim.
ur a fan of math? holy shit ima fan of online/app calculators and ready to go programs that i just plug shit in
I have dozens and dozens of lost neutral stories.
Showing up with the fire department, melted computers - best one is bosses brother describing how important it is the only disconnect the RIGHT neutral- and pulled out the WRONG one…
I've watched your videos for about 2 years. People are gonna love you, and people are going to hate you. Unfortunately, that's life. KEEP posting these great videos with real world examples beyond "perfect textbook scenario". If they don't like it they can start their own channel and dethrone you!
I'm a 45 years in the trade retired sparky. Thanks for the class for the younger kids. Well done!
Thank you for explaining the math. I've wondered about it. I experienced this when the 60-year old feeder to my parents' house wore through its neutral rubbing by on a tree that had grown. It was definitely presenting as a haunted electrical system with lights brightening and dimming and stuff not working. The electric company folks knew exactly what was happening when I described the symptoms. I pulled the main breaker and they rolled a truck to put a new feed on the house at midnight, bless them. We lost a TV and the oven, but the expensive stuff survived. Now I know both what it looks like and how to calculate the damage.
So glad that you made this video...kids now-a-days really don't "see" these equations like they should.
Love that you put the full wheel up as well...not something you see very often :)
They absolutely do if they go to trade school.
Great explanation. Another weird situation is when you loose half the circuits in you house but when you run the electric dryer those circuits get powered again.
Really? Wow!
@@Bidenlost2020 Yes, the voltage (one side 120 volts) goes thru the dryer ( or electric range) back out the other side of the 240 volt coil and then to the 120 volt LOADS
that have no voltage supplied, BECAUSE that side is open. @Wcospider5
@@tedlahm5740 Interesting.
@Ted Lahm Can you explain this further? How is the dryer supplying power to the 120 loads in this case if the wiring to the 120 loads is open?
@@tedlahm5740 I'm sure I'm being dense, but I still don't understand how this is wired (miswired really). I understand that the dryer has a 240V circuit comprising both legs of the phase, but how is the 120V string wired such that it doesn't have power when the dryer is off (that 240V circuit is open) yet the 120V string does have power when the dryer's 240V circuit is closed? Is a neutral shared with the dryer but also switched by the dryer switch in addition to the 240V circuit being switched by the dryer switch or ?
I've been playing with wires since I was a kid and have a good understanding on how electricity works and have even helped wire houses but watching these videos and the way you teach not only makes me feel like a kid again but it's a wake up call that you don't know everything you should know if you are a DIY'er. Cutting corners by not knowing the hidden dangers is no excuse for not educating yourself to better understand how electricity truly works. I greatly appreciate you sharing and breaking this down, you are probably saving someone's home or better yet, their life! A+
Thank u. Ive been trying to explain this to my co-workers on why its so important to make sure remote fans only get hooked up with 1 power. They all think since its on the same phaze it wont matter and cancels out, then wonder why their lack of cold welds at neutrals in the switch box smoked the brand new fans.
the wackiest situation I ever found was a house running on gen set due to a power outage, and since it wasn't a large gen set, they broke out a subpanel for that stuff. The guy who installed the generator moved a few circuits over but failed to realize some were a common neutral in the new kitchen. The imbalance went back to the utility side panel and caused flickering lights in the neighbor's house. (no gen set there) Talk about a haunted house! On further investigation, I found the basement fluorescent lights were also taking some of that flickering power, but nobody went down there on a regular basis.
Great explanation and visual aids for the next generation!! Great job 👏🏻 keep doing what you’re doing
Ok, from the title I wasn't sure because it sounded like you were talking about a 120v multi branch circuit ( multiple outlets on the same 120v circuit ), but yea, what you mean is when you have a *split phase* circuit and you lose the neutral, yea, you get different voltage on the two legs if they have different loads since the imbalance can't return on the neutral. A former co-worker of mine had the neutral break to his house from the pole once and this is what happened: one leg browned out while the other leg went over voltage and burned out some of his equipment. I had something similar happen myself once. My oven heating coil melted down and shorted out against the chassis of the oven. Apparently the control knob of the oven only bothers to interrupt ONE phase, but not the other. So ONE side is always hot, and the chassis is always tied to ground, so other side that is always hot kept current flowing through ground and kept heating the oven, even though it was OFF.
Thank you for always sharing your knowledge .
Thanks for this video. The breakdown was eye opening especially with the formulas. Keep them coming.
I have seen countless melted neutrals because the DIY or handyman connected both circuits onto the same voltage, that caused massive neutral overloads. I have gone on hundreds of no power calls because of that condition.
This is all great! I learned all of this when I attended BE/E school on the Navy(pronounced Bee Doube E), or basic electricity and electronics. You can still find the module handouts online. Kind of like black and comic books, called NEETS, Navy Electrical and Electronics Traning Series.
Nice explanation, I was wondering when you were going to break this down, every time I try to explain this I end up confusing everyone so now I can just send people the video! Thanks D!
Excellent representation of what occurs sharing a neutral.
Another great and instructive video. Thanks for your instruction.
Very informative and well articulated.
Fantastic presentation!
This is a very nice comprehensible presentation, congrats! 😁
I would love to see a video on backfeed in a circuit. What is it? How can it happen? Etc. thank you as always for the detailed explanations!
If you're referring to back feeding neutral in MWBC, then he already has a video on it. But if you're referring to how a backup generator can back feed utility lines when both main breaker and generator breaker are on during a power outage (which is why interlock kits are mandatory), then sure, I'd love to see Dustin's POV on it.
very well illustrated !!
As a newbie helper 35+ years ago. I recall being sweaty with bare forearms on an AC duct screaming to my electrician. "MONROE! White wires can't shock you, right?"
I should have waited for his answer.
I'm not an electrician and actually understood everything in this video he did such a great job explaining. This guy is sharp.
One question that came to mind when you were explaining what happens in an open neutral, was, does this video explain the kitchen scene of the movie 'The money pit", where Tom Hanks is in the kitchen, sits down to read over the contractor paperwork, turns on the lights, and the sparks fly as the wiring is burning up the wall, over to the outlets, tiles popping off, the counter appliances turning on, speed up, he pulls the coffee pot plug and watches the TV set blow up, and the refrigerator smokes, and then everything else goes south !??, or was this a Hollywood prop setup?, I think that this describes your open neutral video, please let me know, thanks 😊
We lost the neutral in our entire house branch thanks to a windstorm a couple of weeks ago. Thankfully the local utility co was out within a few hours and had us back up and running. It completely separated from the service line feeding the house.
Good explanation -- thanks!
Nicely done, professor
Nice video! Thanks.
Nice explanation. The neutral in the service to my house opened several years ago. Three receptacles blew out of the wall, several switches fused, Romex melted, and so on. Most of my stuff blew up. Tragically, it occurred during the one week I was between insurance policies.
I rewired my house after work using a Coleman lantern for light. It took two weeks, and another week for the electric company to replace their effing underground service. They, of course, called the disaster "an act of God" and avoided any liability.
Bastards.
Under no circumstance should the romex ever melt. Both legs in the romex are supposed to be on their own circuit breaker to interrupt if current goes high enough to melt the wire. Loss of neutral is only a problem for appliances since the voltage can go too high on one leg to fry the appliance, but not get the current high enough to trip the breaker. Breakers are there to protect the wire, not the load.
@@phillipsusi1791: Oh, I get it, but this was really extraordinary. Fortunately, most of my family was here when it happened. I had six circuit breakers with welded contacts. I lost my fridge, dryer, furnace, computer, printer, two televisions, etc. Light bulbs literally exploded. Four surge protectors burst into flames. If no one had been home, I would have lost my [mortgaged, uninsured] home.
@@edwatts9890
Damn!
Thank your sir, your nice explanation.
I think that what is important to conceptionally understand some of this was not emphasized. That is, that each 120 volt circuit is out of phase with each other. This more clearly explains the voltage difference with and without the neutral.
Yep, another way to think of it is: relative to the black phase, red-to-neutral is -120V
Incorrect. That is what the taught you in college while using an oscilloscope. Transformers are not wound in opposite directions to make that happen. There are three sine waves associated with 120/240 volt 1 phase 2@ 120 volts and 1@ 240 volts. They all start at the same time and all travel in the same direction. No 180 degrees out of phase. Think it through how a transformer works and directions of electricity travel, before you respond. Respectfully, Kevin
@@KevinCoop1 You're right. It's not a phase issue. I didn't learn that in college. I was trying to make a point and used as you pointed out a commonly incorrect term.
Thank you brother 💪🏼
When I bought my condo, wired throughout with common neutral, the water heater had been replaced with a on demand and the had used shames breakers to make room. Both new breakers were wired with both sides of a common neutral circuit on the same breaker which could cause overload of the neutral. 20amp 12 guage.
I’m a retired industrial electrician. We ran many 3 phase 208 w/neutral, we had some cord ends lose connection and burn up expensive electronics and other components
D’oh!
That's why code says that if you are running a 2 or 3 phase circuit, it must be hard wired to only ONE load, or a sub panel that then has its own breakers in it.
@@phillipsusi1791 I don’t think I understand. These were machines with motors, electronic controls single and 3 phase loads in one machine
Monte, If I understand correctly, you ran a 3 phase 4 wire branch circuit out to a point and made a cord connection to a machine that had 3 phase 208v loads and single phase 120v controls. The neutral failed and the 120 volt controls were hit with higher voltage and fried. Unfortunately that can happen and there is no fix other than well done terminations and maintenance afterward. Best wishes, Kevin
@@monteglover4133 Oh, I thought you meant you had multiple outlets going to different outlets with different devices plugged into them. Yea, one device that returns some current over the neutral to cheap out on an AC/DC converter that can only handle 120v input will blow that part out if the neutral fails. I never liked it when they made clothes dryers switch to a 14-50 outlet with a proper neutral so they could legally keep using a 120v AC/DC converter instead of just making them spend another nickel on a converter than runs off the 240v.
Great video, very interesting.
MORE NERDING OUT!!! Thanks Justin!
Bravo my friend!!!
Everything great in the video, just one slight correction:
3:05 Actually, that’s not Joule’s law. 🤓
Some people call the equation “P = V I” as Watt’s law. Whether it was discovered by experiments or not, it can be mathematically proven by using the definition of power (P = E/T), voltage (V = E/Q) and current (I = Q/T).
Joule’s law (as an equation) is: P = I^2 R. This can mathematically derived by substituting Ohm’s law (V = I R) into Watt’s law.
Thank you. Question though. What happens to my V meter if I measure between Hot and the now disconnected Natural. Wouldn't I now be completing that circuit with the other hot ? Even though Natural isn't going back to the panel, it would be connected to something else at the branch.
And I wonder if this what vaporized my RV's DC board at a park where I plugged into a 110 outlet but got 220 V.
Great info on this and in depth. In what instance would you run into a toaster and a TV plugged into a receptacle on a 240v circuit? I assume in a kitchen, but normally wouldn't they make these 120v 20amp circuits?
DUSTIN, Most Multi Branch Circuits are going to be Unbalanced Loads so when the neutral is open or out of circuit, what do you recommend doing to PROTECT the loads and circuits from getting damaged? Aren't there Over-voltage protection circuits or what do you recommending using to sense the hot lines or sense the neutral line when its open? a sensing circuit or monitoring circuit should be connected to the HNH lines
Love your channel. I've been doing a crash course in electronics watching your videos; learning so much. One thing I'm still curious about. I have heard different answers in different applications. Let's say I want to hook up a main disconnect switch in between my main service and a subpanel. If I'm using, say, a 10-3 plus ground (2x 120 V hot conductors, one grounded conductor -- neutral, and a ground), do I include the neutral in the switch? In other words do I break the neutral when I break the loads at the switch? If so, what can you say about the order of disconnect/reconnect?
Series/ Parallel circuits, Ohm's Law, grounding & bonding... gotta know all of it or you're not an electrician. And if you're not careful with MWBC's you could lose a lot of money in property damage and that's not what you want to have happen. Time in the classroom is SO important in the electrical trade.
I liked the math lesson and enjoyed the way you presented it. I once experienced a neutral interruption and it wasn't a good thing. However I was hoping to see a short video of a TV exploding at the end.
Dustin, as a Licensed Journeyman for more than 55 years , I understood everything you said and showed in the Video but I could never explain it as good as you have done . And in my 55 years of installing electrical branch circuits , Residential and Commercial , I have never wired any circuit as a Multi-Branch Circuit ! Each Circuit should have it's own Neutral as it should be except on 240 Circuits that don't require Neutrals and that would mainly be circuits for Welders and some heavy duty motors according to the manufacturer's specs.
Yes, this pretty much shouldn't be possible on an individual circuit if you follow code. It can happen for the whole building though if you lose the neutral coming from the pole.
Where I am, you can pull 1 neutral to cover all 3 phases. For example, circuits 2,4,6 can share 1 neutral. Circuits 8,10,12 can share 1 neutral. It’s fine and works but I do agree I rather each circuit have it’s own neutral.
Starkly, If you run a feeder to a sub panel, you are doing the exact same thing as a multiwire branch circuit. I’m guessing not two neutrals there. You say you have done commercial projects? Have you ever wired office partition systems that have 4 circuits? Do you run separate neutrals on parking lot lighting projects? I find it hard to believe you always run separate neutrals.
@@joshlavecchia9888 That's perfectly fine as long as all 3 phases and the neutral are either going to a single load, or to a sub-panel. The single load will either return no current on the neutral, or less than the maximum current on any of the 3 legs. Since the neutral can carry the same current as any of the 3 legs, it can't be overloaded.
The problem is that in wiring projects for buildings that are not single family residential, it's quite common to run multi-wire branch circuits. Try quoting a job with individual runs against a competing quote with half the number of runs. These aren't going away, at least in commercial settings.
Pretty much every house in Phoenix AZ built before AFCI’s is loaded with multi wire circuits. They often used them in the kitchen for a refrigerator circuit and a countertop circuit. Even bedroom circuits were wired multi wire.
Honestly, I'm shocked if you see a dedicated fridge circuit before '96. (Which means '98 the way the builders do things in the Valley.)
@@bradleyhcobbI’ll have to check next time I’m in an early 80s house. I know that I’ve seen many 1997 and 1995 houses with dedicated fridge circuits. I was also just at a house from 1986 with a dedicated one but the kitchen was fully remodeled and stuff was moved around so they could have changed the circuits around. I’ve never seen a dedicated fridge circuit in a 70s house, just tons of aluminum and multi wire circuits.
@@everythinghomerepair1747 I just inspected a '96 today. No dedicated circuit for the fridge.
GFCI wasn't required more than 6' from the sink until '96 (which means builders didn't start getting it right until '97 or '98) so the fridge is often on the "other" circuit.
My father-in-law just lost the neutral in the line to his home (ground wasn’t apparently enough to compensate), and fried his furnace, refrigerator, and several other appliances.
Are there any protection devices which can be wired in at the box or outlet to protect appliances from such a failure?
Really awesome video
Great video. I've often wondered why the USA does not SLOWLY transition the kitchen refrigerator circuit over to 240V? I believe the motor would be more efficient and the total power consumption lower. Thoughts?
it's been suggested many times, but the locations of a fridge are not always convenient for rewiring and that would also mean 20-30 years of transition, even if it were forced on everyone. Now consider that a kitchen is not the only place to have a fridge. I see fridges in garages, back porches, pantries, pool houses, and even in office spaces or a medical lab, where there's no 240 available.
We can’t even be bothered to transition to the metric system so…
@@trickhealey ... we did try that about 45-50 years ago and what little we did was VERY costly, only to get a lot of static from those who didn't want to change. Just replacing all the road signs was a crazy amount of money. Also consider that everything in commerce would need to be changed as well. Gas pumps, scales, and all other measuring devices, along with all consumer packaging. How about industrial and transportation where everyone changes from pounds to kilograms or gallon to liters? There are some big safety concerns here if a pilot or truck driver is not familiar with his load.
@@rupe53 quite complicated indeed. The Gimli Glider (Air Canada Flight 143 7/23/1983) flight crew and passengers can attest to that particular hazard.
I’m too old at this point to even convert my thinking into metric. I would never have an intrinsic understanding of the quantities without converting in my head, it would be maddening. Temperature too, can’t seem to get comfortable with the numbers meaning anything to me. Tell me it’s 23°C and I don’t have a clue what to wear! They just changed my local highway exits from being sequentially numbered to being defined by mile marker. I will never know the number of the exit I live near again, can’t get it to stick.
Hard as it is to accomplish, I did design a model airplane using metric measurements and it was so beautiful to not have to think in fractions. It is quite interesting to me when I imagine how the standard of measurements we use shapes our perception of the world.
@@trickhealey ... I have been around long enough to remember many of the common metric items. like 23C would be short sleeve weather... 0 is freezing and 100 is boiling. Also, - 40 is the same for F & C scales. (friggin cold) 25+ mm for an inch, and 39+ inches in a meter ... but don't get me going on using mile markers for exits. That's just insane. How are you supposed to know if you missed an exit if they are miles apart? I was just at exit15 and now it's exit 25? Did I miss one... or two?
I should try to take some pictures of the wiring in my house that I'm fixing. There is a 12/3 multi-wire branch in the dining room running on 2 singles pole, un-tied breakers to run 2 ceiling lights. That's tied into a 12/2 running a security light. That's tied into 2 other 12/2 branches in my kitchen (which have their own single-pole breakers), which are tied into my bathroom. This circuit in turn was tied into my HVAC, which also had its own single pole breaker. That's tied into a receptacle in the living room, which was then tied into a multi-wire branch circuit running in conduit to a detached garage.
Did I mention this is also running on a 125 amp Federal Pacific MLO panel?
Wish I had this guy in my apprenticeship school
The TV would actually most likely survive as most modern consumer electronics use switching PSU’s that are rated 120V-240V or even 100V-250V in some cases.
I undid a couple connections under a refrigeration unit once and literally heard the sizzle and smoke release from four cash registers at a store once. That is how I learned about MWBC from the sparky. I still think it is a dumb idea.
The TV is not a good choice to use in your example, as it will likely draw 600 watts no matter what the input voltage is. The situation is much more complicated when you include switching power supplies in the scenario
Assume a spherical, purely linear TV in a vacuum
@@benchociej2435: Ignore gravity.
I was thinking the same thing. If you have a switch mode power supply it’s possible the TV MIGHT be happy with a toaster in series. Then again I worked on TVs back in the 90’s that had floating power supplies and the whole chassis floated at 170 volts because they didn’t have a transformer. We could only use ungrounded oscilloscopes to test them. The toaster would still be very unhappy and would probably have a hot chassis though. I’m going to start testing all my outlets every morning…
All circuits in any 120/240 volt system share a neutral, that is the neutral in the service entrance.
so when doing residential electrical with multi branch circuits apart from cost.... wouldnt having a five wire home run solve this issue ? i.e put all the red hot wire connections on one neutral and have a separate neutral for everything connected to the black hot wire connections and have them share the ground wire for clearing ground faults ? and u balance the breakers and oads as u other wise normally would . wouldnt that prevent the lost neutral unbalanced load voltage split ?
Could u do some videos about solar system and battery storage system, how they connect with each other, and how they connect to the gird…. Thanks
i hate "shared neutrals". The biggest builder in my area wires all their houses with MWBC's. You lose the utility neutral and half the house loads are smoked. I'm an electrical instructor at US Steel. I teach all of this in NEC class, great job, I'm gonna take a 15 minute break and just show this video.
With the voltage imbalance, since it's an AC circuit, wouldn't the voltages switch each cycle which load gets the high voltage? So the toaster would get 240 and the TV get 180 but then on the other half of the sine wave the TV would get 240 and the toaster like 200. And you would get a really messy sine wave
Kirchoff’s law bit me in the posterior when the neutral wire in my generator feed came lose from the outdoor plug. The generator’s neutral was floating and not bonded to ground and there were energized circuits on both phases. Fried some LED fixtures, a refrigerator motherboard and a Waterpic. It took awhile to figure it out because the voltage at the generator was 120 on each phase and also measured 120 in the house because the current through a multimeter is only a few milliamperes. It was only when I measured the voltage drop across an actual load that the answer became clear.
Im not an electrician, but i'm more an electronic technician. I want to point out the overall point is true, the math was spot on, and its likly the tv will stop working, but in real life what actually happens will be a bit different. The short reason why is that the TV is not a simple load with an unchanging effective resistance.
The switching power supplies takes the 120vac, rectified it, smooths it, and DC to DC down converts it to the rest of the TV circuits. The DC to DC systems are freqently tolerant of a higher input voltage. But the output voltage is regulated and so long as nothing has broken yet, the TV load's apparent resistance or rather impedance goes up because your feeding it a higher voltage but it's actual wattage use is internally regulated and stays mostly the same. But with the TV in a serries circuit with the toaster, the now higher impedence of the TV creates an even larger than 180vac voltage drop across the tv. Which will probably result in exceeding the voltage raiting of the smoothing capacitor or some component in the DC to DC converter.
The power draw of the TV will likly remain largly the same untill the tv breaks. The results is the same, and the TV stops working, but the cause will likely not be because of excess power draw, ratherly it will likly be because of exceeding voltage raiting of some component of the TV.
The real world differences stem from whether an appliance presents as a fixed or not fix resistance or impedence to various voltages.
Most modern electronic devices will adapt and work fine if the expected 120v input goes up to 240v. An old incandescent light bulb or a toaster won't.
@@phillipsusi1791 It makes sense that an appliance with switching power supplies be made to work with either 120 or 240.
If the incoming neutral breaks then the neutral cable voltage will get to the equipment cases which could shock you. The more balanced the system the smaller the voltage. In the UK where they have single phase 240 V the full 240 V can get to your electric car if the PEN wire breaks so they must have special protection against that.
Weird things can happen if the incoming neutral breaks. There is a video where a house started to use the cable TV connection as the neutral. This could kill a cable TV operator if he broke the cable.
I had a weird thing happen with an install we screwed up. We roughed in a garage with a studio above, and all the plugs were reading reverse hot and ground. And in the panel one of the lines was 0 volts to ground and the other line was 240v to ground. So what happened was that the installer bonded the ground to the neutral in this panel which was a sub panel :/ once I undid that everything went back to normal, but I just dont understand how things were even working normally or why the voltage was reading out like that! The people weren’t using this building very much but it had been lived in for a little bit and it seems weird that with 240v to ground on that one line, that they didn’t have worse problems. Could you maybe explain how this happens?
How is loosing the neutral any different than having an open normal 120v circuit?
Im not understanding how loosing the neutral changes the voltage at the device, since the only place the two hots are paired up at is at the. breaker? Wouldnt it just not have any return path and simply not function?
Maybe what im missing is it depends on where the neutral is lost.... like if the neutral was lost on the homerun, wouldnt it just be to open 120v circuits? But then if its lost in some random place thats when crazy voltage at devices happens?
🙌🏽🙌🏽🙌🏽 now how would would fix/find/ or replace this neutral in a residential home. I’ve seen people connect the ground to neutral at a receptacle but I don’t like that.
Why would you replace them? Not a common problem. Just make sure your neutrals are tight in your panel board every few years.
@@KevinCoop1 wouldn’t be my panel lol 😂 but I’ve ran into some homes with situations where it’s 120 between the neutrals and grounds
@@devontekendrick8313 that means the bonding jumper in the panel is not installed.
GV. Couldn't keep up with all the math but totally understand not enough vs too much. 1 doesn't want to work and the other protected itself. Believe that's what you was saying.
Never assume all circuits on a multi wire branch circuit are sequentially landed. I’ve seen circuits picked up in different locations in older panels. For instance, 2 , 4 and 12
Could you please give a more realistic example of a multiwire branch circuit with an unbalanced load? The TV/toaster example is a bit confusing for me because I'm having trouble seeing what this type of circuit would look like in the field. Thank you. Love your videos by the way. Been following you for about 5 years now and learned a lot from your videos.
I'm not an licensed electrician but when I watch what your videos, I feel like I can play one.
Big fan of the channel and all the effort put into production, honestly.... But I have to say I'm pretty disappointed about the failure to address the blunder video regarding current measurement through a multimeter. Did I miss a follow up / correction somewhere?
1st year ape; would the condititon hes describing during 14:10 only be detectable by burning shit up by using things under load? or would i be able to see 180 V on that part of the circuit when there isnt a load on it? my smooth brain makes me think itd say 240 V?
i know i worded this poorly i spent all day in a trench telling my jw i forgot to take the rags out the pipe after i glued them D:
Great lesson. Losing that neutral if it's on a combination breaker will roast that sucker. Had a plumber jump power off temporary pole for me and got about 6 combos for me and burnt his wet vac up. Had to throw that in there😂
I assume that "combination breaker" means a double breaker that is tied together to give both phases for a 240 volt load. If that's the case, then the load may not even have or need a neutral. Dryer outlets used to not have a neutral for this reason, but dryer manufacturers realized that they could run the electronics at only 120v if they used the earth ground as a neutral, and that's why dryers were forced to switch to a 14-50 outlet that has a neutral, since you are not supposed to return current on earth ground under normal conditions. It sounds like your plumber effectively did the same thing and tried to split the 240v circuit to only get 120v, and if you lose the neutral when you do that, then the two legs go out of balance and you get higher voltage on one and lower on the other. At that point you can only hope that the overcurrent on one leg will trip that breaker, and since it is supposed to be mechanically interlocked with the other, it will take that one down with it. This doesn't always happen though since breakers are there to protect the individual *wire* not the *load*.
@@phillipsusi1791 a combination breaker I’m referring to is a Arcfault single pole. I wasn’t on the job site when the plumber decided he needed electric and ran a 10/2 to instead of a 10/3 to meter socket and tiled the neutral on one of the a or b lines from sub-feed temporary thus putting the ground and neutral on the isolated neutral bar! This reading 180 V on one leg and 60 on the other. Fried arc fault breakers on high leg and smoking his wet vac and ruining 6 arc faults (combination) breaks.
@@dgibson6147 I'm still not sure what "combination" refers to in a single pole breaker.
About that Elecctrician U theory book 📙...
Kind of a weird question let’s say you lose your neutral from the transformer would all your neutral circuits in your house, be completed through the ground and would it work OK since they’re bonded at the main service panel?
If the math just doesn't work in your head, then you can safely play with this. Sometimes doing is better than thinking about it.
Buy a laboratory power supply. These are used for doing electronics work. They are DC only.
Get one with two outputs and another connector on it for a ground. Also buy a pack of resistors of multiple values.
These power supplies are "floating". In other words, they have no connection whatsoever directly to the power from the wall. They are also of low voltages. You can safely short any or all of the lines, so don't worry at all about short circuits. These supplies have settings for voltage and for maximum amperage. Short circuit the lines and the voltage drops to only allow amps you set for, which will be zero unless you have a load within the short circuit.
Play around with two or more resistors and you can measure the voltage drops. You can measure the current at each point. The power supply itself will tell you the amps and volts through the whole circuit. Try doing 4-5 resistors in series and measure the voltage drops between different points.
Just make sure the connecting cables and resistors can handle the amps you set for.
(If you want to connect external stuff like an oscilloscope, you will then need to connect the ground on the power supply terminal in front to the circuit because the negative on the oscilloscope is directly connected to your mains ground. Very bad things can happen if you manage to short circuit the oscilloscopes positive from some device device directly to ground! Bam!)
What good is the power supply otherwise? You can pick any DC voltage it does and use it to power something like your cell phone or laptop if you can't find the chargers, just need the right plugs to fit. Need 4A at 5V for your cell phone, but you don't have the right charger, now you do.
until very recently we would use one neutral for three phases. and one ground. recent code changes has one neutral per circuit. so many less circuits now in the same piece of conduit
Can this cause voltage to go up? When I turn on the dryer the voltage goes up to 134 volts on the house and consumers with voltage protectors stops working. What can cause this voltage fluctuations?
If a device (like the TV in this example) is a world voltage device (100v-240v) would this example cook the TV? Just curious.
The TV likely won't be damaged by this 'lost neutral'. It might end up acting like it is in a brownout depending on how the other circuit and other devices on its circuit behaves. The analysis in the video is not correct for basically every digital device.
My quick and dirty analysis for the a lost neutral is something like this: assume every device on both circuits will at some point see the full 240V. Any devices which are not rated for this voltage are likely to be damaged.
It would be great if you did a video on having to back feed a circuit that went dead, and there's no way to abandon it !? Thanks 😊
So if the volts will drop that low down to 60 with the resistance go up
The simple answer is smoke - and possibly fire due to over and under voltage - and the various incorrect current due to that over / over voltage.
“Volts down - amps up - that’s the ways its Eff’ed up!”
Many years ago had a computer lab (think 30 user computers and monitors in a room) that lost a neutral. Pop. Pop-pop. Pop-pop-pop. Monitors fry in turn as they get too high a voltage, die and in doing so reconfigure the load to pass more voltage to other ones.
I lost the main neutral from the pole. A roofer hit the neutral and bottom wire on the main feed from the pole. There was no insulation on the wires.
Inside the house the current tried using ground which was tied to the water line per code. However, the water line was lead, not copper. This melted a hole in the water line which was the main line. The shut off valve was in a pit in the basement floor, so it filled up with water and energized, but the valve was rusted open anyway.
Had to call the water department to get the supply shut off at the street and the electric company to shut off the power.
This house had an old fuse box with a 60 amp capacity. It got melted. Any devices with digital circuitry got fried. It was a disaster.😮
ima have to rewatch this video many times
Yes, he gave MUCH TOO MUCH information for a new learner.
You need to go way back to the beginning.
Learn about Kirchhoff’s voltage and current laws first.
Then go the Ohm’s law. V=I*R and E=I*R. are the same equation. The V and E are both voltage. Yes more confusion.
@@tedlahm5740 ima look into it thank you
@@tedlahm5740 is this like the line voltage and phase voltage?
@@richardc7433 You are jumping WAY AHEAD. That has to do with transformers.
Delta and Why transformers have line voltage and phase voltage.
Unbalanced loads really grind my gears. One nut is tryna squeak out a teaspoon full and my left ones tryna play old faithful.
Joule-Lenz law,[1] states that the power of heating generated by an electrical conductor equals the product of its resistance and the square of the current:
This is NOT the same as Ohms law for Power. And Ohms law is for DC or for purely resistive loads. When AC is involved you have an added component which is Frequency.
Example: You can measure a coil with an ohm meter and come up with a resistance. With this known resistance and known DC voltage, you can calculate the current (E/R). Now if you apply that SAME voltage but with AC you will get a whole different current flow. Because AC introduces Frequency into the calculations. At resonance frequency of a coil of wire the max current will flow and this can not be calculated by simple ohms law (E/R). This is because when voltage is applied to a wire, a magnetic field is created, when voltage is removed, the magnetic force collapses into the wire, thus generating a voltage. When the times of those voltage are exact, the coil is at resonance and max current will flow.
With AC the resistance is called impedance. In DC resistance & impedance are the same.
Then there is a PF to include in AC circuits....
exactly what ive been tryig to tell a insurmetation guy whos has this issue on some plugs sept i cant figure out where the 3 wire splits off like theres a hidden box in a walll
Sounds like multiple code violations.
@@phillipsusi1791 how it was built in the 20's
@@1ajs Well yea, code changes over time.
This is why most job specs these days require a dedicated neutral for each circuit.
My eyes have been opened. Is this related to why I lost my television during a lightning storm?
So, toaster draws 3x wattage compared to tv. In a series circuit this means the tv voltage is 3x compared to toaster since a series circuit each seeing the same current and P=IE. 60v toaster / 180v tv. it helps me to intuitively see it and back it up with the math.
This reminds me of a situation concerning multiwire branch circuits...
A customer was changing a 30 amp 240 v laundry center washer/dryer to a separate 120 v washer & 120 v dryer. I wasn't quite sure how to make the conversion. I wanted to separate each leg of the 2 pole circuit to make two separate 20 amp 120 v circuits. My dilemma was this... I know that the laundry circuits had to GFCI protected. The receptacles were going to go behind a stacking washer & dryer which made it very inconvenient for a point of use GFCI receptacle. The washer & dryer would have to be disassembled & moved to press the GFCI reset button if needed. I was going to put the multiwire branch circuit on a double pole 20 amp GFCI breaker with one leg powering the washer & the other leg for the dryer, but I had the feeling that this would cause nuisance GFCI breaker tripping due to different currents on the neutral. I ended up capping off one leg of double pole circuit & putting the 120 v dryer on the remaining leg. I put the washer on a GFCI protected general lighting circuit. I know laundry is supposed to have it's own designated circuit, but running a new designated circuit would have required a lot of invasive demolition from the panel to the laundry area. Would placing the washer & dryer on separate legs of a double pole GFCI protected circuit have caused the GFCI to constantly trip? What was the solution? Would I have had to run new circuits to the laundry area? It's a pretty uncommon situation to encounter since 120 v dryers are pretty rare.
If you use a two pole GFCI breaker and wire everything properly nuisance tripping will not be an issue, these special breakers will have L1, N and L2 on the load side, and you will connect the pigtail neutral to the neutral bus unless the panel is a plug-on neutral design. They are designed specifically for multiwire branch circuits, 120/240V circuits, and 240V circuits. For 240 volt loads that don't require a neutral you would simply connect the black and white to L1 and L2 on the breaker, and connect the neutral pigtail. The white wire in this case should be wrapped with a piece of black tape to identify it as a hot wire.
I dont know if this is related but... i lost ground on a residential entry at my appartment a while back. Everything was now 240 and it burnt all my bulbs, outlets were at 240, ceiling fans almost welded together and worst of all, my landlord wo7ldnt take my advice and he was playing in the old style breaker box bare handed. The ground lost was outside, from the post to the house. Anyways, it was costly.... computers went, also
You did not lose ground. From meters to pole mounted transformers have 2 Lines and 1 neutral. No ground involved. But you were very close. The lost neutral on the service does the same exact thing as this video.
@@KevinCoop1 okay, i might have mixed up ground and neutral. Anyways, it was a dangerous situation my brother explained. He is a electrical engineer, specialized in nuclear
Joule's Law states that H (Heat) = I (Current) x V (Voltage) x T (Time the current is allowed to flow). Or, written differently, H (Heat) = I2 (Current squared) x R (Resistance) x T (Time the current is allowed to flow)....
I think you would want to call it Watts Law... Watt's Law: W = V x A x p.f. wattage equals voltage times current times power factor. For purely resistive loads, such as heaters, or light bulbs, the power factor equals 1.0. (single phase)
1:34
I Would Like To Make An Important Precision..
Even if loads are not balanced, if you put your clamp meter around a neutral, you read nothing.
The Only way to mesure amps on a neutral, is to put you meter probes in serie.
I don’t think so.
Have to agree with the Flux capacitor guy on this one. I’ve taken current readings on a neutral with an amp probe many times
when using 3 wire with shared neutral, i would always put them on the same phase but separate breakers
Really, you’re going to overload your neutral
Not even an apples-to-oranges comparison; more like apples-to-sand. Pretty much every modern TV has a "universal" switching power supply that works on 100-240V mains. On the other hand, pretty much any toaster is a purely resistive load. The TV has active circuitry that keeps the digital circuitry happy regardless of the mains voltage.
I was thinking the same thing. Even "simple" loads now have universal SMPS. So, the exact situation depends on the loads type (constant power, resistive, or motor loads)
Either way, balanced loads on a shared neutral is the best approach. And the unlikely event of a shared neutral open fault and independent load fault.