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!
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.
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.
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"_
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.
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...
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.
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.
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
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!!
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...
@@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.
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.
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
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... 😳
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.
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.
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.
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. 😲
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.
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.
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.
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.
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).
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.
@@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!
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.
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. :) )
@@IronFinger66 As a Degree holder (English B.A) let me say that having one these days is barely something worth shouting about. Obviously this isn't true for all, and I'm not saying it doesn't apply to me either, but some of the dumbest, most closed minded people I've ever met I met on campus. There's plenty that can't be taught in a classroom or through a book.
I worked on a circuit last week where a boiler was fed from two different circuits - sadly not uncommon. A switch fed the supply to the boiler but a programmer was independently fed from another circuit. The boiler actually had its own breaker in a recently upgraded board marked central heating. The problem is isolating that circuit only isolated the supply. If the homeowner had switched on the heating while I was working there, 230 would have been lurking around on the switch wire. I got rid of all that and ran everything from one fused spur. I also had to change that because the original switch was unfused. It's a potentially dangerous situation that is easy to miss
It seems the code requires a disconnecting means insight of the equipment. at least for A/C's on residential set-ups. It need not be fused as its protected at the panel, this rule is so no one can juice up the system with someone wrkg on it.
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.
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
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...
I have EXACTLY the 1st situation you explained: upstairs lighting. Except both circuits were ceiling lighting in a 1.5 story cape code house. My solution is to make the 2 circuits a single circuit. I'm trying to decide if I bond them together in the panel which may confuse someone working there, or to bond them in the wiring near the panel. Since these circuits are old knob & tube, I'll probably have to bond in the panel with a Warning Label explaining the situation. One point to make is you can SERIOUSLY OVERLOAD the Shared Return. IF you had a full load on both circuits, you would have the COMBINED LOAD ON THE SHARED RETURN. W/15 amp breakers, you theoretically could have 30 amps on the return. BUT since these are typically 100% lighting, that never happens. You should have seen what happened when not knowing my situation, I decided to balance the load by placing one circuit on each of the mains legs (!) No breakers blew, but load imbalance destroyed all the surge protectors I had on all my electronics and there was definitely the smell of "burnt electrics." This was after maybe 10-30 seconds of energization. It was torture wait to see if I started a fire in a wall, but the house had good knob and tube construction practices so there wasn't enough time to burn off all the insulation and radiantly heat the wood until it caught fire!
My bet is he is not that's why he is so clear and crisp. That's why he knows what he is talking about. If he was a college professor he'd have no idea what he was talking about.
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
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.
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!
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.....
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 .
The neutral can have a significant potential if the loads on the electrical gear is not well balanced. The large neutral currents can cause voltage drops along the neutral if its not sized properly.
YUp was wrkg industrial, told to hook up lamps on 277 v told brkr was off and what # it was, check w wiggy, hot was dead, made sure by turning on that brkr, it was live, turned off, it was dead. YET something told me to go between the white and the ground. there was over 140 volts due to the imbalance of loads on a 277/480 volt Wye. it was the 1st time I did industrial but somehow I knew there was a dangerous situation the boss never told me about. Someone is eitha gonna die or have a serious issue working with that boss. This was in Worcester Mass.
We sometimes have circuits similar in the US with a shared neutral, but our 2 phase wiring can make a broken neutral wire very problematic for anything plugged in to them 😏 Because adjacent circuits in our panel (consumer unit) are 120v but 180 degrees out of phase, take away ground and you could have 240v going through a 120v appliance. Of course you won’t know it right away instead the hair dryer won’t work and then someone turns on the microwave and suddenly both pop and blue smoke comes out.
so, how would this be an issue, if the wire that would power a light is a 2 wire, line and neutral cables in one wire. if you were to add a circuit wouldn't the neutral be added from the 2 wire from the circuit that you are branching off from. I see how this would be an issue on a diagram, but not actually done.
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...
It's a mistake to connect lighting circutzs (which are basically single phase) to a three phase MCB (which is designed for 3 phase equipment, such as a 3ph motor). Lighting can be spread across three phases in order to either balance the load or, in industrial applications, to avoid any stroboscopic effect that may make rotating machinery appear stationary. In both cases, single pole mcbs should be used with each circuit having its own neutral. The other issue with using a 3ph MCB is regarding isolation, as all lighting would need to be off when, for instance, changing a single fitting on one of the phases. Otherwise good vid 😉
But this (I think) is actually allowed in the USA. For what they call "half-switched outlets". Where a line conductor is taken from a lighting circuit (and fed via a switch) and connected to one socket of a duplex socket, so obviously the line interconnection between the two sockets has to be broken, by removing a small tab, but there is no requirement to remove the interconnection on the neutral side meaning that the line may be supplied from a lighting circuit and the neutral may be supplied from a socket circuit.
Tapping the neutral of a different circuit is not permitted in the USA.. In most cases the "split duplex" receptacle is served by the same circuit.The other possibility is the two halves are served by a three wire circuit (both hot wires with shared neutral), protected by a two-pole breaker..
Interesting video as always. Thanks for your time. AT 10:20 you mention that you don't especially like the configuration you mentioned. Our house is like that (UK) and I just wondered... what approach do you take and why? Thanks again for your time.
The most popular alternative to a split load configuration is using RCBOs which are essentially just miniature circuit breakers with individual RCD protection, meaning in the event of an earth fault only 1 circuit will be isolated instead of the usual 4-7. Another nice feature is that in the event of a Neutral-Earth fault on a typical split load unit the RCD for the affected circuit will remain un-resettable even if the breaker is turned off, with RCBOs it would only be the affected circuit
Dr. Lecter Thanks but that wasn't my question. I was interested in JW's comment about not liking the split of light cvircuits between upstairs and downstairs. I get the message about borrowed neutrals ;-)
Colin Herbert The problem with the twin RCD arrangement is that a fault on one circuit will affect several others, and without testing equipment it is not obvious which circuit has the fault, leaving the occupier of the property literally in the dark until the fault can be found and removed. RCBOs for all circuits is far better, as any fault only affects that particular circuit and it is immediately obvious which circuit has the fault. It costs a bit more, but the advantages are well worth having. You would still normally split the lighting into 2 circuits as with the twin RCD arrangement, unless the property was very small.
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?
Thanks John as always. A couple of questions/comments: How do you discover a shared neutral in testing? I did an EICR at a property recently before replacing a CU, but it wasn't until I put the up and dn lights on seperate RCBO's that I realised there was a problem. Maybe my testing procedure needs to be updated!? Secondly, I am not very happy with putting up and down lights onto one circuit. If you get a fault on one circuit you loose all the house lighting. I appreciate it is the pragmatic approach.
Switch on all the lights, and leave them on. Isolate at the consumer unit, remove the L&N wires for all of the lighting circuits and test for insulation resistance at 250V between each set of wires, so LN1 - LN2. If there is a shared neutral it will show as very low resistance between the two circuits. Same can be done for all other circuits if it's suspected that there are interconnections between those - but you do need some loads connected to each circuit otherwise the problem will not be revealed.
Thanks John, yes I see it is really important to have all the lights on. I did manage to coorect the issue yesterday, as it was, it was quite straight forward. The house had been rewired in 1968. Will test for them in houses of that era in the future.
@@dogwalker666 Yeah the usual situation is to have one fuse in a 3 phase disconnect blow, but the other two fuses are still intact, which often happens on HVAC equipment, which usually ends up blowing up a compressor if there's no interlocking in the equipment.
here in the UK it is not as common a problem as in the USA where we use split phase boards... and the electrician that installed forgot to install the breaker connector when they made a split circuit sharing the neutral and the ground... which as why most of us were trained to turn off the circuit plus the circuit breaker above and below it until we fixed it... just in case it was a split circuit.
your end part of the video actually showed the exact reasons I run into a lot of times... in the caribbean and the USA, but, another reason is due to how many jack leg electricians have only dealt with the basic old fuse panels, and do not know what they are doing. They assume that neutral and ground are identical because the primary panel in these countries almost always has the neutral and the ground connected to the ground rod. Because they have never worked with sub panels or been trained, they do not know that the neutral is actually coming from the light poles, and that there really is a difference. The ones with no training are the electricians that hurt the most. Here in the UK, most of the residences have a ground that comes from the utility as well as the neutral and the live... big difference... not as many ground spike systems here.
What if you're wearing rubber footwear and you touch the neutral line before the damaged wire or a live wire . Will you still get a shock as you insulated from the ground?
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.
😁 Brilliant information just what I've been looking for, have the landing stairs..
6 років тому
But downstairs you said if you are grounded ie touching the ground you get a shock but if you are upstairs how are you connected to ground to get the shock?
Most common building materials are conductive to some extent, and even if you are totally insulated there is still capacitance to consider. It's extremely difficult to remove yourself completely from the ground, and the amount of current to cause a noticeable shock is tiny.
Hi i was thinking of renting rooms out, So first floor 16mm tails -Consumer unit covering a kitchen corridor lights. Then 4 x 10mm cable to a garage fuse box to supply a radial and light cables. X 4 rooms. Apparently this is how small hotels are wired by my electrical friend . Could you cover some possibilities. Also maybe a electric meter to keep a check on used electric Thanks
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!
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. 😳
I have also been shocked by a shared neutral, fortunately only 110 volts across fingers of one hand. it's very common to share neutrals in America, I guess it saves on pulling extra wires. I do believe that it should NOT be called neutral, but name of ' common ' wire also does not suggest that it CAN be HOT. A new name should be used, even the' return' wire designation might be preferred in conversation. When dealing with 230 volt, I am VERY careful not to assume that there is no shared return.
The example of the stairway lights is confusing to me. Is it a matter of running a two wire cable as shunts/travellers from a three-way switch fed on the first floor to a three-way switch on the second and using a bootleg neutral from that box out to the light? Seems like if I were to do that much work to begin with, I'd just pull a three wire (+E) cable to begin with... We use the term "shared" only for split or three phase neutrals. What you described in the stairway lights would be a bootleg, or stolen, neutral and has been illegal for many decades.
PetrosArgy Yes, two wires between the switches, with the line on one floor and the neutral on the other. That arrangement isn't permitted in the UK either, but can be found in plenty of older properties. Why it was done in the past is not entirely clear, although it may be due to the installer not having 3 core cable, as that would typically be the only place 3 core & earth cable would be used, everything else would use 2 core & earth. Using three wires is the correct method, and is what would normally be used on new circuits.
***** It might have been the common practice in the distant past of using a single-core cable plus a 2-core instead of 3-core for two-way switching that made this kind of thing more likely. Take it away and there's no reason not to do it properly.
Just to add - in Australia the usual way to do a two-way is using a pair between the switches, then a single to the load from one switch and a single to the supply from the other switch. The Neutral would be another single picked up from the ceiling somewhere near the light. The neutral was never brought to a switch. Also, it's almost impossible to buy 3-core cable unless it's twin+earth, so every electrician keeps a roll of single core in the truck.
![Branch Circuit, Multiwire, NEC 2020 - [210.4], (19min:38sec)](/img/n.gif)
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!
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.
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.
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!!!!!
Just to say,I really appreciate you time and effort,I have a load of qualifications,but I find your posts very interesting.
By a galactic distance the most informative man and videos available! I am recently qualified and spend hours watching JW! Many thanks
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.
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...
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.
First time anyone has explained this situation and I actually understood what they said! :)
Exactly 💯
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.
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!
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!!
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.
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.
Thanks to your video, I could fix the mess I discovered in the wiring of my staircase lighting. Thank you John!
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
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 :)
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
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... 😳
@ Zentrobi - A borrowed neutral would warrant a code 2 if picked up when undertaking an electrical installation condition report in the UK.
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.
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.
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.
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. 😲
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.
Excellent safety video. I bet your information has already saved someones life. Thanks
Im newer to the Electrical world and I love your videos!
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.
This was a great explanation and to me as an American also hilarious, the dry deadpan English delivery and the Stewie t-shirt 🤣🤣
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.
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.
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).
Thank you Mr. Ward for this excellent presentation. -Respectfully
I just assume everything is live, even when proven otherwise. That's probably the safe bet, considering I'm not an electrician.
Paralleled neutrals is code violation... maybe not where you live (?) Reason: magnetic fields, overheating, etc.
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.
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!
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.
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
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. :) )
You sir are a genius thank you, better than all my electric teachers put together.
I second that
John, did you do an electrical degree? Also what's your day job? I've learned a lot from you as a (soon to be) graduate and I was curious.
You don't "do" a degree, your earn a degree.
@@Rico702Vegas arsehole
@@IronFinger66 😂
@@IronFinger66
You have earned that title too.
@@IronFinger66 As a Degree holder (English B.A) let me say that having one these days is barely something worth shouting about.
Obviously this isn't true for all, and I'm not saying it doesn't apply to me either, but some of the dumbest, most closed minded people I've ever met I met on campus.
There's plenty that can't be taught in a classroom or through a book.
Great visual example!!! So on a new home I could test for this fairly easily with a meter!
Very informative. Solved an issue i was having in an old house I just moved to . Thanks
Occasionally I work on equipment that has switched neutrals -that can be a bit of a pain to fault find on lol.
Germans like to switch the neutrals, or grounds, in the P/A/VW automotive world....
I worked on a circuit last week where a boiler was fed from two different circuits - sadly not uncommon. A switch fed the supply to the boiler but a programmer was independently fed from another circuit. The boiler actually had its own breaker in a recently upgraded board marked central heating. The problem is isolating that circuit only isolated the supply. If the homeowner had switched on the heating while I was working there, 230 would have been lurking around on the switch wire. I got rid of all that and ran everything from one fused spur. I also had to change that because the original switch was unfused. It's a potentially dangerous situation that is easy to miss
It seems the code requires a disconnecting means insight of the equipment. at least
for A/C's on residential set-ups. It need not be fused as its protected at the panel,
this rule is so no one can juice up the system with someone wrkg on it.
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.
Thanks John, very clearly explained. That's cleared things up for me.
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
You only get a shock if you are grounded OR you complete the circuit.
Jose Martinez from Texas. first wishing you and yours best of happy holidays. Awesome video. You make an amazing teacher. Thank you.
I'm not alone in still thinking that lives should be red, at least in my imagination
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...
I have EXACTLY the 1st situation you explained: upstairs lighting. Except both circuits were ceiling lighting in a 1.5 story cape code house.
My solution is to make the 2 circuits a single circuit. I'm trying to decide if I bond them together in the panel which may confuse someone working there, or to bond them in the wiring near the panel. Since these circuits are old knob & tube, I'll probably have to bond in the panel with a Warning Label explaining the situation.
One point to make is you can SERIOUSLY OVERLOAD the Shared Return. IF you had a full load on both circuits, you would have the COMBINED LOAD ON THE SHARED RETURN. W/15 amp breakers, you theoretically could have 30 amps on the return. BUT since these are typically 100% lighting, that never happens.
You should have seen what happened when not knowing my situation, I decided to balance the load by placing one circuit on each of the mains legs (!) No breakers blew, but load imbalance destroyed all the surge protectors I had on all my electronics and there was definitely the smell of "burnt electrics." This was after maybe 10-30 seconds of energization. It was torture wait to see if I started a fire in a wall, but the house had good knob and tube construction practices so there wasn't enough time to burn off all the insulation and radiantly heat the wood until it caught fire!
Awesome video JW. Keep up the good work mate. 👍
Are you a college lecturer? Your commentary is so clear and crisp, and you make the subject matter easily understandable.
My bet is he is not that's why he is so clear and crisp. That's why he knows what he is talking about. If he was a college professor he'd have no idea what he was talking about.
twn5858 lmao
Those that can, do. Those that can't, teach.
Those that can, do. Those that can't, teach. And those who cannot teach... consult.
Those who can, do; those who can't, teach; those who can't teach, teach "gym". (Woody Allen)
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
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.
Why would you still get a shock on the neutral even when you're wearing shoes?
Well explained. Thank you for sharing your knowledge.
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!
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.....
Thank you JW. Your calm demeanor helps with visualization. It would be too easy to misjudge assumptions. No second chances. 13DEC2017
Thank you for the explanation very helpful and well explained .
You my friend are a legend. Your videos have helped me a lot. Please keep up the good work :-)
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 .
The neutral can have a significant potential if the loads on the electrical gear is not well balanced. The large neutral currents can cause voltage drops along the neutral if its not sized properly.
YUp was wrkg industrial, told to hook up lamps on 277 v told brkr was off and what
# it was, check w wiggy, hot was dead, made sure by turning on that brkr, it was live, turned off, it was dead. YET something told me to go between the white and the
ground. there was over 140 volts due to the imbalance of loads on a 277/480 volt
Wye. it was the 1st time I did industrial but somehow I knew there was a dangerous
situation the boss never told me about. Someone is eitha gonna die or have a serious issue working with that boss. This was in Worcester Mass.
We sometimes have circuits similar in the US with a shared neutral, but our 2 phase wiring can make a broken neutral wire very problematic for anything plugged in to them 😏 Because adjacent circuits in our panel (consumer unit) are 120v but 180 degrees out of phase, take away ground and you could have 240v going through a 120v appliance. Of course you won’t know it right away instead the hair dryer won’t work and then someone turns on the microwave and suddenly both pop and blue smoke comes out.
so, how would this be an issue, if the wire that would power a light is a 2 wire, line and neutral cables in one wire. if you were to add a circuit wouldn't the neutral be added from the 2 wire from the circuit that you are branching off from. I see how this would be an issue on a diagram, but not actually done.
John, would you do a video on a socket outlet with broken neutral. Thank you for your great videos.
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...
It's a mistake to connect lighting circutzs (which are basically single phase) to a three phase MCB (which is designed for 3 phase equipment, such as a 3ph motor). Lighting can be spread across three phases in order to either balance the load or, in industrial applications, to avoid any stroboscopic effect that may make rotating machinery appear stationary. In both cases, single pole mcbs should be used with each circuit having its own neutral. The other issue with using a 3ph MCB is regarding isolation, as all lighting would need to be off when, for instance, changing a single fitting on one of the phases. Otherwise good vid 😉
But this (I think) is actually allowed in the USA. For what they call "half-switched outlets". Where a line conductor is taken from a lighting circuit (and fed via a switch) and connected to one socket of a duplex socket, so obviously the line interconnection between the two sockets has to be broken, by removing a small tab, but there is no requirement to remove the interconnection on the neutral side meaning that the line may be supplied from a lighting circuit and the neutral may be supplied from a socket circuit.
Tapping the neutral of a different circuit is not permitted in the USA.. In most cases the "split duplex" receptacle is served by the same circuit.The other possibility is the two halves are served by a three wire circuit (both hot wires with shared neutral), protected by a two-pole breaker..
Interesting video as always. Thanks for your time. AT 10:20 you mention that you don't especially like the configuration you mentioned. Our house is like that (UK) and I just wondered... what approach do you take and why? Thanks again for your time.
Colin Herbert You always make sure the two circuits are separate. That means correctly running 3C+E upstairs.
The most popular alternative to a split load configuration is using RCBOs which are essentially just miniature circuit breakers with individual RCD protection, meaning in the event of an earth fault only 1 circuit will be isolated instead of the usual 4-7. Another nice feature is that in the event of a Neutral-Earth fault on a typical split load unit the RCD for the affected circuit will remain un-resettable even if the breaker is turned off, with RCBOs it would only be the affected circuit
Dr. Lecter Thanks but that wasn't my question. I was interested in JW's comment about not liking the split of light cvircuits between upstairs and downstairs. I get the message about borrowed neutrals ;-)
Colin Herbert The problem with the twin RCD arrangement is that a fault on one circuit will affect several others, and without testing equipment it is not obvious which circuit has the fault, leaving the occupier of the property literally in the dark until the fault can be found and removed.
RCBOs for all circuits is far better, as any fault only affects that particular circuit and it is immediately obvious which circuit has the fault. It costs a bit more, but the advantages are well worth having.
You would still normally split the lighting into 2 circuits as with the twin RCD arrangement, unless the property was very small.
Colin Herbert It was the twin RCDs I don't like, not the division of lighting circuits.
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?
JW, you the best keep up the informative videos man !!
can you do a video of how to safely add a loop of sockets to an existing loop?
Thanks John as always. A couple of questions/comments:
How do you discover a shared neutral in testing? I did an EICR at a property recently before replacing a CU, but it wasn't until I put the up and dn lights on seperate RCBO's that I realised there was a problem. Maybe my testing procedure needs to be updated!?
Secondly, I am not very happy with putting up and down lights onto one circuit. If you get a fault on one circuit you loose all the house lighting. I appreciate it is the pragmatic approach.
Switch on all the lights, and leave them on. Isolate at the consumer unit, remove the L&N wires for all of the lighting circuits and test for insulation resistance at 250V between each set of wires, so LN1 - LN2. If there is a shared neutral it will show as very low resistance between the two circuits.
Same can be done for all other circuits if it's suspected that there are interconnections between those - but you do need some loads connected to each circuit otherwise the problem will not be revealed.
Thanks John, yes I see it is really important to have all the lights on. I did manage to coorect the issue yesterday, as it was, it was quite straight forward. The house had been rewired in 1968. Will test for them in houses of that era in the future.
Sir, at some stage you need to do a video where you play that wonderful organ... please.
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.
"If some moron decided to..." Lol
Well it happens a lot when using fuses.
@@dogwalker666 Yeah the usual situation is to have one fuse in a 3 phase disconnect blow, but the other two fuses are still intact, which often happens on HVAC equipment, which usually ends up blowing up a compressor if there's no interlocking in the equipment.
@@mysock351C yes to mean to fit a thermal overload.
here in the UK it is not as common a problem as in the USA where we use split phase boards... and the electrician that installed forgot to install the breaker connector when they made a split circuit sharing the neutral and the ground... which as why most of us were trained to turn off the circuit plus the circuit breaker above and below it until we fixed it... just in case it was a split circuit.
your end part of the video actually showed the exact reasons I run into a lot of times... in the caribbean and the USA, but, another reason is due to how many jack leg electricians have only dealt with the basic old fuse panels, and do not know what they are doing. They assume that neutral and ground are identical because the primary panel in these countries almost always has the neutral and the ground connected to the ground rod. Because they have never worked with sub panels or been trained, they do not know that the neutral is actually coming from the light poles, and that there really is a difference. The ones with no training are the electricians that hurt the most. Here in the UK, most of the residences have a ground that comes from the utility as well as the neutral and the live... big difference... not as many ground spike systems here.
I read somewhere that two circuits can share a neutral if you use a tandem circuit breaker
They can, same applies with a 3 pole circuit breaker.
Perfectly explains why daft buggers like me end up swearing and cursing because we couldn't be bothered to turn off the supply.
You make great videos. Thanks for sharing.
What if you're wearing rubber footwear and you touch the neutral line before the damaged wire or a live wire . Will you still get a shock as you insulated from the ground?
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.
you make it very interesting John thank you
😁 Brilliant information just what I've been looking for, have the landing stairs..
But downstairs you said if you are grounded ie touching the ground you get a shock but if you are upstairs how are you connected to ground to get the shock?
Most common building materials are conductive to some extent, and even if you are totally insulated there is still capacitance to consider. It's extremely difficult to remove yourself completely from the ground, and the amount of current to cause a noticeable shock is tiny.
Hi i was thinking of renting rooms out, So first floor 16mm tails -Consumer unit covering a kitchen corridor lights. Then 4 x 10mm cable to a garage fuse box to supply a radial and light cables. X 4 rooms. Apparently this is how small hotels are wired by my electrical friend . Could you cover some possibilities. Also maybe a electric meter to keep a check on used electric Thanks
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!
Really valuable piece of information..
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. 😳
Just wondering is it possible to put a outdoor socket in my fish tank as the tank fits into my unit and no room for socket.
What configuration do you prefer/install John ?
I have also been shocked by a shared neutral, fortunately only 110 volts across fingers of one hand. it's very common to share neutrals in America, I guess it saves on pulling extra wires. I do believe that it should NOT be called neutral, but name of ' common ' wire also does not suggest that it CAN be HOT. A new name should be used, even the' return' wire designation might be preferred in conversation. When dealing with 230 volt, I am VERY careful not to assume that there is no shared return.
Broken neutral you touch it and are NOW in series with the lightbulb?
The example of the stairway lights is confusing to me. Is it a matter of running a two wire cable as shunts/travellers from a three-way switch fed on the first floor to a three-way switch on the second and using a bootleg neutral from that box out to the light? Seems like if I were to do that much work to begin with, I'd just pull a three wire (+E) cable to begin with...
We use the term "shared" only for split or three phase neutrals. What you described in the stairway lights would be a bootleg, or stolen, neutral and has been illegal for many decades.
PetrosArgy Yes, two wires between the switches, with the line on one floor and the neutral on the other. That arrangement isn't permitted in the UK either, but can be found in plenty of older properties. Why it was done in the past is not entirely clear, although it may be due to the installer not having 3 core cable, as that would typically be the only place 3 core & earth cable would be used, everything else would use 2 core & earth.
Using three wires is the correct method, and is what would normally be used on new circuits.
***** It might have been the common practice in the distant past of using a single-core cable plus a 2-core instead of 3-core for two-way switching that made this kind of thing more likely. Take it away and there's no reason not to do it properly.
Just to add - in Australia the usual way to do a two-way is using a pair between the switches, then a single to the load from one switch and a single to the supply from the other switch. The Neutral would be another single picked up from the ceiling somewhere near the light. The neutral was never brought to a switch. Also, it's almost impossible to buy 3-core cable unless it's twin+earth, so every electrician keeps a roll of single core in the truck.