SHARED NEUTRALS The Dangers of borrowed neutrals, the problems they can cause and some solutions
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- Опубликовано: 17 июл 2021
- This video explains what is meant by the term “Shared Neutral” or sometimes called a “Borrowed Neutral”.
We are often asked why it is dangerous if everything is working normally, or so it would seem.
So … with the aid of simple circuit drawings we will show you what a normal installation should look like, how we get borrowed neutrals and when and why they can represent a danger to life.
Finally we will offer some solutions to make the circuits “safe” again.
This video is No.79 on our RUclips channel where we have videos on a wide range of electrical topics.
To see a full list of all our LearnElectrics videos, click on the link below.
/ @learnelectrics4402
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Always work safely, electricity can be dangerous. If you are unsure, stop and seek advice.
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In america u can share a neutral in some cases. Its called a multi wire branch circuit. If u have a multiwire branch circuit it is required that both circuits disconnect simultaneously. You do this by using a double pole single throw breaker. Where both breakers are connected together at the throw. Thus u cut one off the other automatically cuts off aswell. Only used on equipment though. And if 2 circuits feeding equipment share a neutral one piece of equipment cannot consume more than half of the ampacity of the multi wire branch circuit.
That's different and interesting. Thanks for the input. Dave.
That seems to be an danger of shared neutrals as well. Feeding the load of two 20amp breakers on to one 12AWG neutral for instance. Seems you could exceed the capacity of the wire.
@@LarsDennert read the full message again. I explained that part in the last sentence...
@@isaiahb.5868 I'm agreeing with you but most people won't notice the danger
cannot consume more than half?? how if it's common trip? what will limit the current at half the breaker rating?
So informative. Plain english. Nothing much like it on RUclips. Keep em coming 👍🏼👍🏼
Thanks for the great feedback. Very much appreciated. Dave.
I am an electrician n from Ghana.
I learn more about electricity from you through your RUclips page.
That's good to know Bashiru. Keep learning, lots more videos to come. Dave.
Excellent series. So clear and concise. I'm not even an electrician, just a DIYer with an interest in electrics, so these are very on point. Thank you.
Glad they are useful Gary. Thanks for watching. Lots more to come. Dave.
thank you very much now i can send this vid link to explane this problem ...great stuff
Glad it helped and thanks for watching. Dave.
Had an electrician change the plug in fuse distribution board where we live with a modern RCD board. The single hall light where the board is tripped the breakers, and not the stair lights with changeover switches.
To solve it the electrician had to put both lighting circuits onto the same breaker.
If the circuits are sharing neutrals this will happen. The RCDs will not see a balanced input and output. Glad its sorted and thanks for watching.
You’re a brilliant teacher. Thank you
You're very welcome, thank you for watching. Lots more to come.
Thankyou for taking time to do these excellent video's, the information is super useful and you make it very easy to understand
Thank you John. lots more to come. Dave.
Excellent educational material, thank you for producing this material for the rest of us.
Glad you enjoyed it, lots more to come and thanks for watching. Dave.
Nice job explaining this. Thank you.
Glad it was helpful Vince. Thanks.
Great videos and really easy it understand. Thank you
You are very welcome, glad they were useful. Appreciated comments, thank you. Dave.
Thank you for your efforts again. Really informative video .
Thank you so much. Great feedback.
Really nice and full of knowledge. Thank you Teacher
Very welcome. Glad you enjoyed it.
Thanks mate. Learning this helped today. Your a star.
Glad it helped, keep watching. Dave.
Thankyou for the knowledge
Thank you, glad you enjoyed it.
As usual. Really well explained.
thank you. Great comments. Dave.
Good lecturer.
May God increase your knowledge.
I hope he does Bashiru. Every day is a learning day for all of us. Dave.
Hi Dave. Just would like to thankyou for taking out the time in creating such fantastic videos. Really appreciate it.
Can you guide me to the video which you speak about basic and fault protection. Thanks again
There is a section on Basic/fault protection in our exam help video number 10 about
Protection for Safety and is on this link ...
ruclips.net/video/eOsz6yWOYqU/видео.html
Thanks, Dave.
excellent video as always. hopefully you can create more content on fault finding
Fault finding is on the list. Thanks. Dave.
In the old days, golden rule was to remove all fuses and put them in your pocket !
That's right, in the toolbox, anywhere out of sight.
no main master fuse back then?
Man i love this channel.
Great comment, appreciated. Thank you. Dave.
Yup, that can be dangerous, say the sparky is on a ladder, the surprise jolt could knock him off
the ladder and cause some real pain, however, what if loads were greater than a few lamps?
say a vacuum cleaner and an electric skillet and a hair dryer, the overcurrent device may be
carrying close to its rated capacity on both circuits but the neutral of one ckt could be carrying
a lot more than what its fuse is rated for and the only time a fuse will blow or a breaker trip is
when the wire heats up enough to cause a fire, then when neutral touches HOT the breaker trips
but the fire has already started.. .
Absolutely. Apparently there are several deaths every year from what happens after the electric shock. The poor guy survives the electric shock part but breaks his neck when he lands on the floor.
@@learnelectrics4402 It is not just about shocks, if you share a neutral with another circuit off or of the same phase leg, the currents will add up, say u have 2 15 amp circuits, that would be a 14 gage wire here in the states. the wire is good
for 15 amps and is protected by an over-current device for 15 amps. BUT if u
share that with another 15 amp circuit neutral on the same phase, (even though
the black wire is protected) The current will be doubled on the neutral wire and
the heat will be quadrupled 4 times even and THAT will start a fire.
Great.... Good job 👍
Thank you Pabor. Thanks for watching. Dave.
Thanks again for sharing your knowledge. As an adult learner I've never understood why this situation is created in the first place. At 3.50 in the video you say the live feed to the upstairs light is taken from the downstairs lounge lighting. What I don't understand is, if you're running a cable upstairs to the light why don't you run 3-core in the first place. Is it as simple as running in singles to save a bit of cable or did 3 core not exist at that time in the electrical industry?
Old methods and working practices, plus they used the two plate method a lot. looping the live between switches and the neutral between ceiling roses. I just used the lounge switch as an example, it could have come from anywhere.
Methods are always changing. Now we are installing smart switches, another change.
Thanks for watching, appreciated.
Great illustration.
Thank you, appreciated. Thanks for watching. Dave.
Thanks Dave.
Hi, excellent explanation and diagrams! Really helpful.
However, @ 4:25, I don’t think the problem is the shared neutral, but the open neutral, because if we implement the solution in option #1 (@ 5:34), and the main neutral is still disconnected, then still all of the wires will be energized.
What do you think?
The open neutral is going to try andffind a path back by sharing with others Thanks for your input and thanks for watching. Dave.
I found one of my living room lights had its neutral shared with a ring socket circuit, was renovating and had access to move the neutral to a junction box with the kitchen lights, sadly all the lights are on one mcb, but it now works when socket ring mcb is off yey :)
Glad to hear that.Thanks for watching. Dave.
once again, great video but i have a question. Would you say its worth testing for a borrowed neutral before a board change to save the headache of finding the fault, if so how would you go about this?
It always helps to know the installation before a board change so that you know what to expect. More on fault finding in a soon to be video. Thanks. Dave.
Always hit the main switch before undertaking DIY electrical work in an undetermined system.
Thanks for watching.
Great 👍
Thank you Sunny.
Top video.
Thank you Matthew, appreciated. Dave.
@@learnelectrics4402 no issues I know all about borrowed neutrals but to be fair never crossed my mind it would go live. Common sense when explained. 😀
That's what catches a lot of people out Matthew.
Thanks for watching.
Dave how would this be coded during an EICR??? C3 C2 C1??? Would the coding be diffirent if the light fittings and switches were either metal or plastic???
Always a difficult one. I would code it as C2 myself. the one's I have come across (not many) have not been immediately dangerous, but could be if a fault occurred or wires removed.
@@learnelectrics4402 Thank you very much for the reply.
This is for here in the states but there is a so called Chicago3-way for turning a light on from 2 places. it involves putting the hot and neutral on the travelers and light on the commons or
poles of the switches, one way is safe as the screwshell is at ground but the other way puts 120 v live on the screwshell of lamp and the NEC prohibits that as of 1923, another style is the
Hollywood or California 3-way weird it is but at least the screwshell is on the neutral side.
I like the names Raymond. Thanks for the info and thanks for watching. Dave.
Meaning to say the diagram at 5.22, the flow can be both ways even though the light is off?
This is the danger with shared neutrals, you think the power is off but parts are still energised. Thanks for watching. Dave.
Hi Dave. Just wanted to know, something regarding extraneous conductive parts. How does an extraneous conductive part become live during a fault. The only item I can think of to make the exposed conductive parts become live is if there is a earth fault on the boiler, which would potentially make the heating system, water and gas pipes to become live. Can you please clarify this. Thanks
good question, have at look at our video -
Exposed and extraneous electrical parts - on this link
ruclips.net/video/MpiwTOSY1gw/видео.html
Until the fuse blows, any connected metalwork will become live. If the cooker casing becomes live and that is connected to a metal light fitting through the bonding then that is also at 230 volts until the fuse disconnects. That is what we want to happen for safety. If everything is the same voltage you can't get an electric shock because there is no potential difference to give you one. that is why birds can sit on power lines. Both feet are at 400,000 volts. No difference, no shock.
@@learnelectrics4402 just a minute ago I came across your video which cleared up any of my doubts etc. Again Thanks Dave.
Excellent.
Is it code along as they are put on opposite legs of the 240
Each circuit should have its own L+N+E conductors. Thanks for watching.
Would you suggest not disconnecting the neutral than in case it is shared. That way it is kept at 0 Volts ?
Michael, sometimes you need to disconnect the neutral. We shouldn't be fearful of every neutral being shared. But it does show the importance of proper safe isolation checks.
Can shared neutrals cause too much current in the neutral. I mean 2 different circuit breakers are supplying that part of the circuit. I know it would be rare but could it happen depending on loads ? Could it be a fire hazard
I suppose if it was 1mm T/E and both breakers were 10A and running at max load. Good point, thanks for the comment. Dave.
I wire my house myself. Add MCB's and wiring, switches etc. DIY
Good luck and stay safe.
I have 2 neutral wires burned at the busbar . My electrician installed the panel 15 years ago and it is only now I noticed as I was installing a new MCB for a Camera system ..... Yes yes I know I'm not supposed to be in there if I'm not qualified before all the spark heads start slatting me ! I have fair knowledge of electrical circuits and would only work at something that I'm confident in installing and straightforward.
Each MCB is independent and don't have and shared neutrals. I did check the neutrals for a loose connection as arcing was my first thought.
They seem all good but the busbar itself is slightly corroded .. the screws being the worst . I have now installed a new wire and bent the ends for better contact ( Original sparky had the two neutrals in one screw , not sure if that makes a difference )
Could slight corrosion cause this and if so why did the rest of them not do this ?
The wire is 1.5 mm solid, Goes to the first led light and onto the next 7 lights at a distance of 30 metres
Again I'm not a sparky ! If I have to pay for someone I will but I like learning the cause and solution of such problems !
Liam, all screwed joints will work loose with time, this is one of the checks that we should do on a Periodic Inspection and Test. Corrosion can be for many reasons, damp, chemicals etc. Isolate the CU and check that all the screws are tight, copper creeps (moves) over time. Remember that with the CU turned off, the two incomers will still be live. Dave.
@@learnelectrics4402 Dave thank-you for your reply ! Yes your 100 percent correct . As it being a damp environment (Farm), it will only accelerate corrosion. Ill take your advise and I'll also change the busbar. Thanks 🍻
Anytime I change a consumer unit, 70% of the time the RCD trips when the landing light is switched on. This is because of a borrowed neutral. The only way around it without altering wiring, lifting carpets, chasing, is to put both circuits on the same RCD. This then defeats the original objective of having the lighting circuits on different RCDs. In the event of a fault the property will loose all lighting.
Sometimes we have to make them choices Paul. Make a note of this and if you do a rewire you can sweep this problem up. Thanks for watching and thanks for the useful comment. Dave.
Do you have any vids on when the light is switched via the neutral?
Take a look at this video on 2 and 3 plate lighting. Switching via neutral is a new one on me, it will leave most of the circuit live. Thanks for the question and thanks for watching. Follow this link ...
ruclips.net/video/NEjCXO_ZC5c/видео.html
@@learnelectrics4402 thanks, was on a job today and it had my brain boggled, I sorted it in the end but I don't know how it was blowing up
@@learnelectrics4402 Here in the U.S.A, in homes built before WWII typically used knob and tube wiring, and switches were sometimes placed on the neutral side rather than the hot like is required for safety in modern practice. Homes from this era could have dangerous 3 way switches, known as the Carter or Chicago 3 way, the hot and neutral connect to the travellers and the light is switched between on the commons, in one of the 4 switch positions the light is live on both terminals but is not lit. This method was prohibited in the US in 1923 but was used sporadically for many years afterwards , as late as the 1960s in rural areas for switching a yardlight from the house and barn, with receptacles in the barn hot all the time and powered by the house, with only three wires in between, excluding the ground.
Another M* Presentation Dave, well done...keep them coming...👍
Super feedback. Thanks Gary.
How's the house sale coming along.
The drawing shows the hot of the second (additional) lamp connected to the WRONG SIDE of the switch.
Thanks for your input.
America here where we use split phase 120V circuits for regular outlet and lights for some background.
I see a lot of people doing this when they add two separate outlets to their garage and they use 12/3 Romex and 1 20A tandem breaker. They will connect the black and red wire to the breaker, 1 for each half of the tandem breaker, and the single white wire to the neutral bar. This creates a huge imbalance in those circuits. If they are pulling 15A on one of the outlets and 15A on the other that is a total of 30A on the single neutral going back to the panel. 10A higher than the wire is rated for. So not only can it be a shock hazard but also a fire hazard. Now in theory it will balance itself out. The real problem is you can turn off one half of that tandem while keeping the other half energized. So now you have a potential of return power on the neutral. Not sure how many people are aware of just how bad a shock you can get from a shared neutral. It will definitely get your attention.
Absolutely right. Thanks for the comments for all to read. Appreciated.
I don't share neutral because it gives room to leakage
Excellent. Thanks for watching. Dave.
It seems to me one major problem that is not discussed is the fact that given two branches with 15A each sharing a common neutral would need twice the capacity ie 30A. Given a feed with #14 would require a neutral of #10. Why is not mention as the #1 safety issue?
Edit @learnelectrics4402 I am being told that on a common return the feed has to come from a tandem breaker one on each side A and B of the panel. Given this for example 15 A on side A + 15 A on the other side B would cancel out as 0 A phase wise. So the worst case will always be 15 A on the return.
Great input. Thanks for watching.