Shared or Borrowed Neutrals on Mains Electricity Circuits
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- Опубліковано 31 тра 2024
- Shared or borrowed neutrals, which are unwanted interconnections between two circuits.
These can often be found in older properties where the stairway light is connected to line from the downstairs circuit, and the neutral from the upstairs circuit.
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Hello John borrowed neutrals are
Very common in hospitals where critical areas are supplied from essential and non essential distribution boards usually single phase boards both on the same phase. And usually find on lighting circuits which are not RCD protected. What can happen quite often is you can electrically isolate a single phase distribution at the source of the supply and then when you prove dead at the board find 230v across neutral and earth. Be very careful as you can prove dead at the board. Someone switches a light switch On supplied from the other board which is not isolated and then the neutral bar on the isolated board becomes live!!!!!
I got the best rattle of my life from a neutral on a mixed circuit, I had isolated the circuit, tested it for dead, and all ok, opened up a neutral junction , where I tapped each of the wires coming into the junction with the back of my hand, and felt nothing, it wasn't until I grabbed hold of two of the neutral wires that I felt the the dirty wallop of the mains return from one arm to the other straight through my chest, the worst part was that had my terminal screwdriver in between my teeth, I clamped down so hard on that thing, I can still remember the involuntary forces. I just closed everything up and nope'd TF out of there. I'll never forget that one.
My best rattle was from the back of a large colour tube TV. Alongside the blinding visual disruption and the involuntary jerk that sent me across the room, I got lingering pain in one knee and one elbow... never did quite work out exactly why. Resistance across cartilage?
Tell you something though... I'd almost get an eye twitch every time I had to take the back off a live TV. A little permanent post-traumatic anxiety made me a far better technician ; )
It's like they say : _"There are old electricians... and there are bold electricians... but there are no old bold electricians"_
@@garychap8384 Always wear rubber gloves in case you slip and try not to lean on any part of the equipment.
Always wear rubber gloves in case you slip and try not to lean on any part of the equipment.
I have found circuits where the neutral colour changed 5 times. Multiple times I have also found earth's being used as lives. Rule of thumb test before touch. Better safe than sorry. A small jolt can throw you off a ladder. So yeah don't fuck around for stupid shit. Just test
Johan Burger of course the old crt runs on ht (if memory serves me right...colour runs on 25kv) and there are serious capacitors in there that hold their charge for a while after turning off.
I had this exact issue when I bought my house and boarded the loft (temporarily disconnecting the wires to drill them through the joists and reconnect exactly as before), upstairs light circuit off. I got a massive belt from the disconnected wire. I eventually found it to be the landing light, live taken from downstairs to the common of a 2-way in the hall then L1/L2 routed via twin (no earth) to the upstairs switch and then the common switched live into the loft (not using the feed from upstairs). All to save running triple between the downstairs and upstairs switches. When I redecorated the landing I ran a twin and earth to the loft from the downstairs to provide the neutral (note this was when I was allowed to do this myself about 25 years ago)! Very informative vids!
"It's not borrowed if there's no intention to return it "... deadpan funny !Keep it up.
Yeh like my neighbour who borrowed my lawnmower and I still haven't got it back yet. Could I borrow a 20 note please!
Lol, Seen many neighbors like yours, they want free bees, don't care if you break your back for it,
Stolen Neutral. Kinda is
Deadpan genius just such a great teacher, all economy no fluff and key information. I would still appreciate John if when you do videos you add links on additional reading to get the theory right and learn more about it.
In the Netherlands, we switch both Line and Neutral at the fusebox. That means that when you switch off the circuit you’re working on, you would immediately measure dangerous voltage on the entire circuit still existing. Well, unless the switch was off and then turned on while you were working, at least...
Do you have a neutral fuse for each group, or do you mean that the main breaker is disconnecting the neutral as well?
@@amanduswestin9211 no, only the line is fused. But the switch (when those were separate devices) switches both. And yes, on modern boards with breakers instead of fuses, if the line trips it will disconnect the neutral automatically.
This is one weird thing about our electrics, (almost?) everyone else only fuses and switches the line.
This was a great explanation and to me as an American also hilarious, the dry deadpan English delivery and the Stewie t-shirt 🤣🤣
By a galactic distance the most informative man and videos available! I am recently qualified and spend hours watching JW! Many thanks
First time anyone has explained this situation and I actually understood what they said! :)
Exactly 💯
Thank you Mr. Ward for this excellent presentation. -Respectfully
Great visual example!!! So on a new home I could test for this fairly easily with a meter!
@ Zentrobi - A borrowed neutral would warrant a code 2 if picked up when undertaking an electrical installation condition report in the UK.
I wish I had seen this video many years ago, when I first started doing interior wiring on my own house. I eventually figured out everything you covered but this would have saved me so much trouble years ago. very useful information.
Just to say,I really appreciate you time and effort,I have a load of qualifications,but I find your posts very interesting.
Did some supply work a while back in a council house, weird 3ph supply, 1ph to house the other 2ph vanished into trunking... but all neutrals came back to the block. I did'nt realise one of the return neutrals was not tight in the block and I disturbed it as I pulled the live cable out of the meter, I heard a buzzing then a pop and blue sparks flew out of the cutout... I s**t my pants and jumped out that cupboard so fast lol took me a minute to work out what was going on.... shoddy engineers out there! I find so many loose neutrals, its bizarre. Solid video as usual Mr Ward thank you...
+Jon “Wookie” Buggins
Neutrals coming loose is well known phenomenon, balanced electrical noise on each phase of higher-order harmonics **adds up** on the neutral shared by the 3 phases, effectively making the Neutral more vulnerable to coming loose than the phases. Though in this case it could indeed have just always been lose, nonetheless worth being aware of...
Excellent safety video. I bet your information has already saved someones life. Thanks
Just happened by this excellent video. Very clear concise and easy to follow. Best ever and finally connected the dots for me about neutral vs ground. Thanks
Thanks to your video, I could fix the mess I discovered in the wiring of my staircase lighting. Thank you John!
Great video JW, it's late o'clock here down under and I'm listning to your videos whilst typing invoices, common neutrals is a real problem in older houses here in Au, mostly when two way switches were added to long halways or stairways, I have even had a case where the sparky installed an outside light and stole its neutral from one of the slab heating zones. The poor customer never understands why a light that has worked for the last eleventy seven years and probably has never even had the globe replaced, has to be disconnected or spend a small fortune on "fixing" it. Thanks for the time and effort you put into your videos.
This is exactly what caught me out replacing a ceiling rose on Downstairs Circuit in my 1960’s built house .... Isolated the circuit by breaker, checked all terminals of the old rose with phase tester & unscrewed wires. When fitting the new one I got a big wallop through my left hand all the way to my chest (with an unintentional yelp..!!) from a neutral wire, one of three. The neutral was live from the Upstairs Circuit.
The other thing I’ll take away from that experience was not to have a head torch pointing directly at a phase tester... because of the metallic reflection from the head torch I couldn’t see that the phase tester bulb was actually lit. Lesson learnt.!!
I’ll bet the lights came on upstairs for that second too... 😳
A very interesting video. I regularly came across 415V three phase and neutral fuse boards before I took early retirement and these were commonly used for lighting. We'd remove fuses to work on separate lighting circuits but I never considered there might be shared neutrals.
We had our house rewired recently. Changed from cartridge fuses to RCBs. Everything went fine with the wiring, replacing circuit for circuit, until the testing. Upstairs lights worked. Downstairs lights worked. Stairs lights tripped both breakers. Ended up putting both lighting circuits into one breaker because the electrician couldn't fix it any other way without tripping breakers.
Great presentation and explanation John - much appreciated! I'm just changing out the bathroom downlights and noticed whilst I was in the loft how shabby the upstairs lighting was and decided that it should be tidied-up somewhat. Took me a bit of time to work out how the upstairs/downstairs 2-Way lighting circuit had been wired (probably done around the 70's) and realised the upstairs 2-Way light (fed from the downstairs lighting MCB) was actually wired into the upstairs light neutrals (fed from the upstairs lighting MCB) which didn't seem correct at first sight and as you've clearly explained it isn't. Many thanks! Just came across your channel - most impressed!!
I needed an ECIR for my rented property, I had to add an additional RCD for lighting circuit, there already was one for the power circuit, so instead of messing about with installing two seperate RCDs I decided to go for RCBO for upstairs lighting and down stairs lighting, one of the upper hallway light on a two way switching circuit shared a neutral with upstairs lighting circuit, so every time someone switched on a hallway light it tripped both RCBOs, I had to run a new neutral for the hallway light from ground floor neutral. At the time it was a puzzle until I put it down on a drawing trying to figure out what the heck was going on.
The best part of the shared neutral in the US is that you have a 50/50 chance of getting on the wrong side of the split phase. Then it goes from 120V to 240V and you will let the magic smoke out of whatever that device was on the shared circuit! 😎 You will know pretty quick something is mis-wired at least, most likely in that hidden junction box in the wall. 😲
man again i have learned so much thank you again you sir are a genius
and generous with information that is very hard to find
Im newer to the Electrical world and I love your videos!
A potentially life saving video. Good work!
Until you listen to 2:05 which could potentially kill you (if circuit is as shown without RCD)
@@peterkilleen3061 I forget that RCDs are not mandatory in every part of the world ;)
@@PhilippMeierGermany yes and even in the uk they are now mandatory on lighting circuit - never use to be… because someone died changing a lightbulb a year or so ago!
People don't understand that neutrals can be overloaded.
If you have too much load on the neutral conductor it will overheat just like a power conductor and if connected to circuits on different supply phases and you get a loose or floating neutral it can feed 240 volts through 120 volt circuits.
Been an electrician for over 40 years and unless I'm hooking up a circuit that requires 240 volts I always make sure circuits in a 10/3, 12/3, 14/3 w/gnd that are carrying 2 circuits with a shared neutral, are only connected to circuit breakers on the same phase.
In the USA, all commons must be tied together in the main panel, and that buss bar has to be connected to earth/ ground. Also, a physical green wire must be run in every conduit, and every junction box must be grounded, as well as each fixture's chassis.
Thanks John, Great video explained very clearly, now I understand why someone would barrow a neutral, as a trainee electrician this has been very useful
Until you do what he says at 2:05 and get a shock!
Thanks John, very clearly explained. That's cleared things up for me.
I love your vids ,really interesting and so well/clearly explained even if I already know the information I still want to watch it .Thanks John
Where I live we don't want to share neutrals randomly because of ampacity but also the possibility of creating a multiwire branch circuit. This is fine at the panel since the neutral is shared anyway but down the branching line losing the shared neutral across the MWBC creates full line to line voltage across the loads in series.
Very informative. Solved an issue i was having in an old house I just moved to . Thanks
I had a similar illegal neutral problem too where a lighting 1mm2 and power circuit 2.5mm2 neutral was connected together at a combo bathroom fan/light/ heater. When we tried to install a RCD on that gpo circuit it would trip when the light was switched on. It was a illegal DIY electrical job done by the previous owner.
Thanks for the video.
Another way to get a shock from the N conductor would be to have a phase to neutral fault on the 3-phase LV distribution network - I think there was a case a few years ago in E. Suffolk where a set of houses received either no power or about 400V depending on which phase they were connected to. I think the N conductor is connected to ground via a current limiting resistor to limit such cases (I might be wrong there) but that's a fairly rare event thank goodness.
Well explained. Thank you for sharing your knowledge.
I worked as a meter engineer for several years. Part of the training was to be aware of borrowed neutrals. These can be particularly hazardous where there is a 3 phase supply in an apartment block. There was at least one occasion when a meter was exchanged ( not by myself) which resulted in the neutral supply to other properties being removed . This caused 415v to be applied to 3 apartments causing extensive damage to electrical appliances. Other instances where borrowed neutrals can be a problem are when the live supply is fed through an RCD and the neutral is connected at two different points, i.e on either side of a time switch. This can cause the RCD to trip.
Very well explained have come across this many times.
Yeah, ran into this the other day, come to think of it I still need to go back to follow up on some things. Another way is to clamp on an inductive amp meter on any neutrals your about to work on. If you have turned of the power to the circuit you are working on and find any reasonable amount of current on associated neutrals then it's a good idea to start turning off breakers until amp meter reads zero (or close to it).
Jose Martinez from Texas. first wishing you and yours best of happy holidays. Awesome video. You make an amazing teacher. Thank you.
Awesome video JW. Keep up the good work mate. 👍
JW, you the best keep up the informative videos man !!
Gah and I BET that's where the netural interconnection was in our old house. I never found it :\ I just tolerated it.
Don't judge, I was young :)
Perfectly explains why daft buggers like me end up swearing and cursing because we couldn't be bothered to turn off the supply.
Very well explained. Thank you!
You sir are a genius thank you, better than all my electric teachers put together.
I second that
😁 Brilliant information just what I've been looking for, have the landing stairs..
very informative.i m in near future upgrading my consumer box with dual rcd and now i can think about separating the neutrals.i dont know how as all wiring is behind the finished walls and under floorboards which have new wood flooring.guess i ll have to work something out .
Thank you for the explanation very helpful and well explained .
Very interesting, I was asking myself this very same question earlier today.
Thank you! John
I'm having 11KV & 3 phase transformer, I'm struggling with Neutral to earth potential (i.e. 24V) also found heavy current similar to phase at some place.
Great video, thankyou,could you show how to do bulk insulation resistance testing at the consumer unit position to find this fault, thax.
Brilliantly explained video John, as are all your videos. I wonder if you could do a video explaining why it is necessary to have a separate earthing system for a Solar PV/battery installation with an emergency power supply off the battery. We have a TT supply and I don't understand the need for an additional earth.
you make it very interesting John thank you
Yeah that’s why we always pigtail our neutrals here. That way you can disconnect the neutral pigtail of the device you’re working on and the rest maintain connection back to the panel. Also if you share a neutral you put the associated hots on a two pole breaker. That way you must kill both circuits involved with said shared neutral
You make great videos. Thanks for sharing.
Excellent videos! more please :)
it might be worth pointing out that in the video at timeline15:33 - 35, at the disconnection point Li to wire, similarly, L2 to wire, usually in close proximity, the hazard voltage is 415v
my mate's house was built in the 1980's and the spark had run a single neutral around for the lights and connected it into the back of a socket. When he had a new split load rcd consumer unit fitted, the Rcds would not latch in and he had to have all the floors up to get the proper neutrals in! One assumes the 'electrician' working on the housing scheme was more used to 12V neg ground systems.....
You can get electrocuted off any 230vac cable.
Pays to always isolate, prove test prove before touching.
You can even get electrocuted off a bonding earth or from a main supply earth cable if the neutral at the point of entry is open or high resistance faulty.
Thank you JW. Your calm demeanor helps with visualization. It would be too easy to misjudge assumptions. No second chances. 13DEC2017
Really valuable piece of information..
Great explanation. I’m still trying to wrap my head around the idea of shared neutrals with timed loads. Not even sure what to call this to learn more, but basically an appliance which turns itself on and off periodically would make the other line with the shared neutral unpredictably hot and cold.
Someone suggested shared neutral with a furnace might cause this?
Another great explanation from JW ! Many thanks!!!
Interesting videos Sir! I am fascinated by the differences between electrical wiring methods between British installations and those here in Canada. Regarding the latter part of the video with the 3 pole breaker supplying 3 loads and having a common neutral: In Canada it IS permitted to utilize a common neutral between circuits supplied from separate phases and protected by single pole devices, albeit the connections to the neutral have to be made so that it is highly unlikely the neutral can be opened accidentally by for example the removal of a light fitting or receptacle... Occasionally this method is used in residential applications as our supplies are "120/240V 1 ph 3 wire" , neutral being derived from the center tap of the distribution transformer.. In some cases 3 conductor cable may be run to a point in the residence and split into 2x2 conductor circuits, each protected by a single pole overcurrent device. ("Split" duplex receptacles as are common here employ a shared neutral just by design but must be connected to 2-pole breakers, nothing to do with neutrals, but just so "joe homeowner" does not turn off 1/2 the receptacle and blow himself up trying to make repairs. :) )
Great Vid John,can you do one explaining 3 phase with no neutral,I struggle getting my head around the subject. Keep up the good work.
Good man I find your work very useful Thanks man, we can’t reward you but God is better in rewarding
May he reward you Amin.
Excellent work John.
I've got a situation in which I have conductors from two circuits on separate phases connected to the same groundless receptacle in a bedroom. I believe the one circuit is using the neutral from the other to make the light fixtures in the basement directly below work. Its a weird situation
Thank you for a very informative video
At 14:00 Another problem not mentioned: If the 3 breakers are on the same phase, then 10A x 3 = potentially 30A on the neutral, also rated at 10A. Iv Seen that. A perfect way to cook a few wires or a whole house!
Thanks for excellent video
sometimes called a 'Loaded neutral' if u borrow a neutral from another ckt on same phase leg,
the neutral currents will + up and you can burn out a neutral even though hot wire was properly
protected.
You’re amazing! Thank you.
Slightly off the subject demonstrated (good video sir) ... Neutral can cause shocks to ground especially exterior, could be wet and techs on ladder where even a small shock could be a surprise and cause a fall off a ladder - especially industrial 3 phase where references to ground are at different potentials all about the property. To avoid shock to service personal, we break both hot and neutral at the device flip switch. This permits safe service of the device and ‘zero potential’ surprises. You would be ‘shocked’ to see the different ground potentials all about a common commercial site. Now, if Hogan grounding had always been the standard... ah’ yes, Chicago did invent entire structural single potential bonding grounding a gazillion years ago. This is where metal structural, plumbing, electrical are all bonded to one single ground conductor cable all the way to the building ground rod system. It provides lightning and shock safety and saves equipment from damage, as well as avoids dissimilar potential corrosion especially of plumbing systems. Originally designed for building over 10 stories tall. If a hot wire comes into contact with any building metal surface, it’s a faster path to trip the breaker. Touching two different metal surfaces won’t cause a trickle shock. Think about a person in a bath tub and the water is referenced to the drain plumbing and reaching up to turn on more hot water turning a metal valve - any potential difference can cause a shock - and so the Hogan ground would eliminate that electrical potential. Hogan was not an engineer, he was a political appointee by the Mayor to head the city Electrical Department, so the street story has been told and passed down through journeyman over the years.
hi, if they took a feed off from the downstairs lighting circuit assuming they used twin and earth why not just carry the neutral as well?
how to get safety mechanism at a home where such type of shared neutral occurs in different phase circuits. Is there any device which could trip if such a situation happens please suggest which to be used for a three phase connection
Thankfully, even when the neutral carries current above the potential ground, it's only 120 volts :-0)
I think that is considered to be "objectionable current". So, if it happens to you, just object!
JC Many thanks for all your videos. Commentary is first class, as I am sure you are aware lol. Are you a natural public speaker or did you have training? Ian, UK Subscriber
I just assume everything is live, even when proven otherwise. That's probably the safe bet, considering I'm not an electrician.
I Did have a shock on a lighting circuit neutral wire.
Carpenter saw Mark on the cable lighten circuit under the floor boards. Had a intermittent problem with lighting circuit. This is when finding the fault that a got a shock from the neutral return wire.
When I found the damage cable,the saw cut the outer casing of the cable and the neutral return wire to the fuse box. 😳
excellent informative video,Thanks John
I got a lovely tickle of a neutral, working on a bedroom light. Isolated the downstairs circuit and tested dead, owner turned the landing light on and wallop...
I am not an NEC egghead, but I believe that at least some version of it allows a shared neutral by design, but the two hot legs must be on a breaker pair that has a tie to ensure they operate together. The prototypical application for this in homes is for the garbage disposal and the dishwasher to be run with a 3-wire non-metalic cable (AWG 14-3 w/ground or maybe #12) and the neutral is shared for the two appliances. The breaker panel will have two 15 A breakers that are tied together for it to be correct (for the reasons you mentioned about borrowed neutrals). Those two loads are generally just a few inches apart, so combining these save some US$$. This sort of separates the men from the boys, so to speak, when it comes to NEC loopholes, and there's surely tons of commentary on just this one circuit diagram.
Good point, I wondered why my microwave and fridge breakers are tied together, even though they seem to be on completely separate circuits. Shared neutral, I didn't even consider that possibility.
I would give that about a 98% likelihood that your fridge and microwave are sharing a neutral and whatever version of the NEC allowed that, the electrician followed the rule and tied the breakers together to ensure safety. It's why breakers have holes and they make ties to connect them. I think I've seen small bolts and nuts used.
Nice explanation.
Now I understand. Thank you.
Thanks for that , excellent
You my friend are a legend. Your videos have helped me a lot. Please keep up the good work :-)
I have no formal electronics training, but I understood the idea is the electrical load is supposed to take most of the potential out of the return to neutral. However, in some cases this is not ideal and a non zero potential can be recycled to the power station. For this reason it was my understanding that the grounding lines terminate in an Earth rod, and do not connect to neutral. I think you have to be part of a circuit to get shocked though, even in the case of hot wires...
Paralleled neutrals is code violation... maybe not where you live (?) Reason: magnetic fields, overheating, etc.
thanks for the video. if someone could explain and help me understand? i thought breakers/GFCIs tripped when a different amount of current returned than what went out. so if there are 2 lights on 1 neutral, and both are on, wouldn't there be a different amount of current on the neutral than went out on each individual hot? wouldn't the current returning be doubled? thanks
Yes, and if a shared neutral is present, the RCD / GFCI will trip all the time.
John, would do a video on a socket outlet with broken neutral.
Thank you for your great videos.
Very informative
Thanks for the video =)
I am confused. If this is an AC circuit, in the first half of the cycle current flows from the source to the load through the "hot" or "line" wire and returns to the source through the "neutral" wire. In the second half of the cycle, the current reverses direction and flows through the "neutral" wire to the load and returns to the source through the "hot" or "line" wire. Does ground/earth now provide the return current?
I hope John ward answers me or anyone.someone to clarify for me,why is neutral earthed and i think the current
would still flow between the two lines in absence of the Earth?It is said earth is at 0v,why does the bulb fail to light when you connect negative terminal to the earth without having another connection to the positive terminal of the battery or vice versa?kind regards for any comment
John, would you do a video on a socket outlet with broken neutral. Thank you for your great videos.
Can a ghost voltage give a shock. I had maybe 35 volt ghost voltage at the fluorescent light and it went up to 130 volt when i took the bulb out. The voltage was causing the bulb to flicker on when switch at wall was off. Apparently the electronic box has capacitors that charge up slowly causing the bulb to flicker on. Thats what i read else where on internet.
Hi John any chance you can do a vedio for intermediate switch controlling 4 or 6 lights. Thanks