Easiest way to describe this. Imagine a 3-way tug of war, the force being the current drawn on each phase. The 3 people pulling are 120 degrees apart. But, they can pull all they want, the central knot in the ropes is going nowhere because it's nailed down to earth. If that nail comes out, the knot would still remain on centre if everyone pulled equally. BUT Once the pull is unequal, the knot will be pulled off centre. The one pulling hardest will have the shortest rope (lowest voltage) And the others will have longer ropes (higher voltage). You can imagine electrically if house 1 (on L1) and house 2 (on L2) are just chilling with a 7W lamp and a 40W TV on, but house 3 (on L3) decides they smell a bit so best go for a shower which is a nice beefy 9.5kW job. He won't be happy because he will be having a cold shower with about 20V. But the other 2 will be getting near 400V because the high load at house 3 has pulled the star point from the centre (neutral) almost all the way over to L3. Make sense?

As an armchair spark I can confirm that something definitely went wrong, at some point, with something, somewhere I hope this has cleared up everything for everyone 👍

Hi Nick Going back to 1980s I remember my dad who's an electrician getting a call from mid terrace house saying that every evening at around 7pm they would get a shock from the sink. So the following day we called in and checked the earth cable to ground (TNCS)and checked earth to sinkand was good so couldn't see why they were getting shock from sink and even the bath was live too. So we decided to come back again before 7 and put a meter on the sink and low and behold it became live at 7pm wow. We disconnected the main earth and tested it, it was live bringing the problem into the house. We found out that the street light directly outside the house had a faulty ballast and was running down to ground and up into the earth rod which was 6 meters away, and continuing through all of the earthing system in the house. Which was on a timeclock set for 7pm every day. Shocking 😅

It's a lost neutral so you effectively get two houses on different phases wired in series across 415v and the voltage divides according to the resistance...as you turn more houses off some poor bloke will get the full wack of 415v if they have the least load...just ohms law

Retired DNO engineer here. The voltages you recorded and displayed in the video do initially suggest an open circuit neutral (probably combined neutral/earth - CNE - conductor on a PME network). The 396V you recorded could also indicate a line-CNE fault that is either (a) downstream of the break in the CNE conductor; this could impose line voltage (400V) on supplies fed on the other two phases or (b) a line-CNE fault with NO break in the CNE conductor on a (very) long main that is fused too highly (typically at 400A). I have seen this more than once where the line-CNE fault impedance was too high to blow the substation fuse due to the length of the main and the line conductor size, combined with the fact that such LV faults tend to be of the 'flashing', transient variety where the heat generated at the fault will cause it to clear spontaneously but not before causing damage to customers' equipment. Keeping in mind that a typical substation fuse response curve will allow about 170% of the fuse rated current to flow for 60 minutes, high-impedance LV faults can cause havoc, although they are rare!

Oh eck! I had something similar. I just finished an electric smart meter instal in an outside meter box for a customer in Cardiff.I had just inserted the fuse carrier into the cutout and the next door neighbour popped around asking if I’ve knocked her supply off. I had noticed there own meter boxes outside and said no you’ll be on your own supply. As I said that I turned to look at the meter I had just installed and noticed the power had gone off. I tested the cutout and it was dead on the incoming side. I rang western power who quickly explained there was a fault somewhere that they were investigating . Apparently over 600 properties were affected! I was proper bricking it until I had rung western power! Lol

Ooh, this one's a bit different then😁 For why there are different voltages. . . the houses would have all been on 3 different phases. Spark Ninja (and his Dad 🙂) did a really good vid / webinar covering some of this. In their case some builder had been digging down the road, found a load of copper in the ground and thought 'yay! off to the scrappies', not realising that copper was the earth grid for an office block, which was now getting 170, 270 and 340v from each phase to earth / neutral. Interesting stuff. The vid's called Earthing and Bonding Part 1 - A SparkyNinja Webinar, and that bit starts at 4:30 if anyone's interested.

This is the state of a lot of the legacy LV distribution network. It's going to be more common the more its loaded up. So with EV, PV and heat pumps or just the push to electric heating pushing more load onto the network the ageing weaknesses are going to start showing. The whole idea in privatising the network was for investment. Our house dates back to the 50's, originally had a 40A main service fuse that was upgraded to 60A in the 80's. The cables in the street are lead sheath, paper insulated (TN-S which is probably now getting very TN-C-S due to repairs) that are coming up to 75 years old and loads have been increasing since they were installed. Over the last 10 years there have been 3 cable joint failures locally. Driving around you can see upgrades in the local HV network being done with substation upgrades etc, line replacements. LV networks upgrades seem to be limited to getting the overground network in villages underground but in towns and cities where re-cabling is going to be expensive has largely been neglected. I think PEN faults and diverted neutral currents (the reason I added a clamp meter to my personal tool kit) are going to start becoming a common problem. Good catch!

The leccy company sent us a letter saying that the power may be off for most of the day due to underground cable problems in our area. Sure enough, out goes the power at 9am on the stated day. Later on that afternoon it comes back on and blows up our gas boiler and the controller for my mum's adjustable bed plus a few other small appliances. We had to make an insurance claim but they were very good about it. So lesson learned. If I get a long power cut now, whether planned or not. I turn off the power at the main board as soon as it goes off. I only turn it back on again once I see the neighbours are back on and working! Even then I only put on the light circuits first and if they are OK, I put on the rest.

I&C metering engineer here, had a call out once to a pub saying that only a few lights where working, so went out tested and found they were only getting 50v with everything on, so immediately turned the main switch off and pulled the fuse, rang ukpn low and behold their main neutral coming into the building via overheard line had burnt out so a dropped. neutral.

Years ago a mate of mine was doing a board change, had pulled the supply fuse, but had left the earthing conductor from the MET to the old board just dangling. During moving about etc, the earthing conductor touched the live side of the supplier fuse carrier and BOOM! Blew the fuse back at the transformer and took out most of the street. He got away with it but had a real job clearing of the scorch marks. A lesson learned when pulling the DNO fuse, make sure there is no risk of anything touching the carrier.

Dropped neutral, essentially sharing the voltage between properties, hence why you saw 400v when the properties where off .. happens loads on new builds, esp on ryefields where someone forgets to connect the neutral

Commercial sparks here. Power guy for BT. I got called out to a piece of kit which senses mains voltages and alarmed up, I got to site and saw voltages varying from 290-305v to earth on the 3 phases in. The onsite generator being from the 70's only monitors low volts not high so didn't start automatically.Anyway fired up the generator which saved any kit on the generator circuits and called our DNO. I went home and they called me shortly saying "we won't need access to your building to check the mains as we now have neighbours calling, with complaints of TV's failing and other kit with electronic power supplies. This was down to cable fault in the area too. However no loss to the neutral or earth.

Big shout out to the Western Power Guys in Devon, we get windy down here and it blows the wires off the overhead insulators and trips the pole out, so OK 4 days over Xmas last year we was off grid on the farm (not a town a farm a mile from the village 1/2 a mile above sea level) the guys have tied our wires to the pole now BUT the last visit the guy said "where's you pole fuse?" so I opened the gate and walked him in "over there" I said , "I'm not to sure of these cows"he said as we walked right through the stock yard "don't worry about cows these are not cows...they are Bulls" OMG his face was a picture !

Brilliant! As an intruder alarm engineer, I attended a telephone line fault for the remote signalling at a house. Luckily, I tested the voltage on the line before connecting a test phone. There was 220v on the telephone line. The house was quiet large and had a small switchboard supplying extensions in each room. Well, I say a switchboard, it was more like a boiled dry kettle full of molten plastic 😂 They too were bloody lucky.

Had very similar on the Diamond Jubilee Bank Holiday in 2012, I was unlucky enough to be on call, call came in from a branch of a convience store we look after saying they are running on emergency power (wtf - They have some self contained EM bulkheads and a UPS on the checkouts) and they had turned the lights off to save power. Got there and nothing was working properly, board cover off, phase neutral voltages were off (but thankfully not by an excessive amount, it was semi reasonably balanced) with some upto 260v. Loop test phase to neutral 22ohms, find main board, thats just the same, Switched off, called DNO, hour later a guy in a small van turned up, explained what we had, and said I think we have a high resistance neutral, said he doubted it, did some checks and said "yup, high resistance neutral" by lunch time the car park had about 4 DNO vans, one towing a mini-digger one towing a generator. It was the dreaded consac (aluminimum CNE conductor, if sheath gets damaged, water gets in and it corrodes away). Another time I will tell the story of the PME terminal 190v above true earth and a couple of confused jointers from NPG!

This is an excellent reminder to us electricians of the symptoms of a broken neutral. We tend to think of this on a PME supply, but it applies equally to TT supplies. My neighbours, who are on a TT supply, had lights exploding, electronics destroyed, the works. This was all down to a broken neutral during a bad storm.

Good informative and interesting video. I had a call out once, where the home owner complained of intermittent dimming lights all over their house. I asked them to turn off main switch and not touch any metalwork. The overhead electrical supply line to the house ran through a number of trees and the neutral conductor had broken. SSEN were called out to repair and trim back the trees!

Great video, as a sparky its really useful to hear because its so unlikely to find it but at least knowing these sort of stories you can learn from them and if someone else sparky or not sees the same thing they can respond in the correct manner... Have to 100% agree, I have had to call out Western Power on a number of occasions because of dangerous situations like holes in cut out accessible live parts to normally warm bitchimin coming out of the top of the cable, even had one where the customer said there was smoke coming out of the top of the head and he just pulled the live out of the head as it was totally loose.. Every time Western power came out straight away and fixed the issue...

floating neutral will do that to ya on 3 phase.. always check your wiring .. and always test the full board.. befor flipping any breakers on after you have done some work on a 3 phase board...

A lost/floating neutral- happens a lot in rural Australia where the aerial 3 phase powerlines (3 Actives plus Neutral/Earth combined) can get damaged by trees in high winds... One advantage we have is running MEN (multiple earth neutral) is that a completely O/C neutral doesn't tend to have quite as dramatic result as that, but you can get quite high earth currents flowing through the earth cables (acting as a 'replacement neutral' back through the earth stake and the neutral/earth interlink in the fuse box) but yes, you can still see some abnormally high voltages (and sometimes some 'cooked' earth cables on the house down to the earth stake from the fusebox- with the 4mm cable trying to deliver the entire houses neutral return current through it!!! 4mm cable trying to handle a 100A plus load- not good!!!!)- Worse it won't trip even RCB's (standard in all newer fuseboxes here) as the A/N supply is still balanced through the RCB's, all the way back to the fusebox neutral bar, where the earth link is now taking the place of the missing neutral!!!

I got called to an office many years ago, some of the rooms had lost lights and power, worked my way back testing eventually to the 3 phase supply in the basement, one phase was dead but the other 2 were the same phase! I went outside into the street to see if there were any lights on next door, then i noticed about 30m along the pavement there were two paving slabs sticking up, took a closer look, saw some arcing in the hole and phoned SSEB, I think the street was dug up and some hefty cables replaced over 2 or 3 days.

Interesting to see the different causes of 400v arriving at single phase supply heads. I have heard of a team replacing supply cables in the road, confusing old and new wiring colours, sending 400v to several properties!

Disconnected neutral. The heavier the load on one phase, the closer neutral gets to them (so their supply sags) and the more the others get (so their supply goes up). The lower the load, the higher your voltage gets, and as things go bang, up it goes even higher. I got called out to a school to replace a knackered network line driver. Opened it up, surge arresters had blown to bits and there were sparkies there replacing striplights. My suspicion was a disconnected neutral while they were working on the main board, but we didn't note a timestamp of when the link went down so couldn't prove it was them. Given their track record though, it was probably them.

I had a similar issue with my home's overhead split phase service cable in the USA. The neutral wire became damaged due to a tree branch rubbing against it. Instead of having 120 Volts on each of the 2 separate supply wires I was getting about 140 Volts on one and 100 Volts on the other - give or take as the house load changed. Since then, I've taken advantage of the UPS battery backups that I have on a few different desktop computers. They have a big display, and you can configure it to always show the voltage. I feel more comfortable every day when I glance at the voltage reading.

Here in the US, we have 240VAC split phase, and the neutral is derived from the transformer on the pole or pad mounted transformer. From time to time I have seen neutral faults, and it can get ugly as well. Because we have two 120VAC legs from the 240V once we loose neutral which typically will feed 1-4 houses, we will see one of the 120V legs start to get close to the 240V and the other leg lower towards zero. Its completely depending on the amount of current happening on each leg at the time. However if you measure the split phase it will still show 240VAC. Neutral will take any path it can usually phone lines or cable TV coax or pipes to try and find that ground path. I had a 2KW UPS in my doom room in college and we lost neutral. That was bad in that flames started shooting out of the UPS, as the voltage spiked way up and the MOV's started to ground out, however the power wasn't shutting off, and because it was a UPS it just switched over to battery as well and continued to push out power. It was a bad situation for sure. Then I had one home that the neutral was going out and it was using the Coax TV Line as the neutral and the coax was glowing red hot. They got really lucky it didn't catch fire. Where is the PEN fault device for the whole house? 🤠👍

The thing to remember is that the voltage in the house is the difference between live and neutral for that house supply. If the neutral is detached somewhere down the street then it can float away from ground towards any of the three phases. If it's your house's phase that it's floated towards then the difference between live and neutral for this house falls, while for a house on another phase the difference rises, up to a maximum of the interphase voltage in the worst case - around 415V. And the thing that causes a detached neutral to float towards a phase is simply a relatively low house resistance between that phase and neutral, which happens for example when someone on your phase turns on an electric kettle or shower, especially when multiple houses on the same phase do this at the same time, ie: in parallel. As doing this lowers the house voltage then people in an area with this fault would also complain of cold showers and slow boiling kettles.

A very under reported fault, not understood by most electricians (why should they until getting to level 4 qualifications where this sort of thing is discussed/ examined on). You have done an outstanding service to YOUR customer Nick and some others too. The DNO should heap praises on you too. Yes, a great idea to cover more of this type of thing in detail. I am out of the game now, but I understand the latest consumer units have earth fault monitoring and arc detection devices. This is thankfully a rare fault, but as the networks in towns and estates age, along with increased loads and much digging up for fiber and new connections, the instances can only increase. All level 3 electricians (whether you feel you are just a domestic or not) need to know and understand. Great opportunity to grow your channel Nick.

If the combined neutral earth is broken the neutral/earth voltage downstream of the break can float wrt the distribution transformer neutral/earth (star point) and true earth. How much this floats depends on how balanced the phases are, the higher the load on one phase the lower the voltage on this phase wrt the floating neutral but the result being an increase in the voltage of the other phases to this floating neutral. The frightening bit is as exposed/extraneous conductive parts are connected to this floating combined neutral/earth they will be live wrt true earth.

So sorry this has happened

Open PEN conductor. Highest load gets lowest voltage

Had this a few years ago in a 20 storey block of flats. Got called there after smell of burning reported. Previous electrician had recorded 400v at residents sockets and multiple appliances blown up. Turns out the neutrals connected at bottom of rising bus bar had been doubled up on one side of the bus bar on the same bolt and had melted the bolt. This then caused 2 phases to have 400v and 1 phase to have 100v. Was a very expensive claim off the cable gang that terminated the offending cables

Its due to the three-phase supply system. When the neutral is disconnected, the star point between the phases shifts around, dependent on the asymmetry of the loads on the different phases. The star point can shift up to your phase-phase voltage for one leg and 0V for another. Do UK domestic sparks not learn about three-phase systems?

Had a very similar thing recently. 400v between the brown phase and earth. Also had cables live when the the rcbos were off 😂 And had the pulsing you mentioned as well. Ended up being a burnt neutral in a 63A switched fuse isolator which was just about making a connection.

Thanks so much for recording this, I have been studying PEN faults and this is very interesting/ scary. You did good!,

Working on a festival in 2012 one of the generators didn’t have the neutral fixed correctly to the lugs on the output. It lasted a couple of days, then one evening I was stood out the back of the Big top and started to hear the fridge trailers running rough and traders looking round as their lights were flickering. Set was isolated and neutral torqued up correctly… We ended up with damaged projector and LED lights. Lucky escape considering the rest of the kit attached to that supply.

I had recorded like 280v at a property on a callout before Christmas, literally as I was chasing an RCD fault I could hear the smart meter humming. Isolated and SSEN came out and the voltage went back to normal…

Hi Nick, this is a fault that I know to be called single-phasing on the 3-phase supply and it happens quit commonly due to eddy currents commonly found in the neutral of a three phase system causing the neutral upstream to burn off before the phases as it is carrying heavier current than the individual phases. Simply if you have two houses with the identical connected load on two different phases the supply voltage will remain at 230/240V as collectively as there will be no current down the common neutral from the point where they join. However if one house only has a light or two on and the other house has an oven, an immersion and some lights running, the house with big connected load will find the supply voltage dropping right down to 100V or so whilst the other house with only a few lights running will find the supply voltage approaching the 400V mark. Effectively, when the Neutral fails upstream, two houses are supplied by two phases with the Neutral only running between the two houses. This situation is potentially very dangerous on a TNC-S supply as the main earth is bonded to the Neutral at the point of supply. If the voltage to earth rises on the Neutral, it takes the MET voltage with it raising the voltage of all exposed metal in the house in relation to true earth bearing in mind that the Neutral at the supply transformer is still bonded to earth as are the PME connections to the point of the fault all providing a path for the excess voltage in the house main earth to pass back to the supply transformer. This situation in the house will be worse if the gas and water supply pipes are plastic. You may have come across electric supply companies now installing earth spikes below the cut-out in new properties - trying ensure voltage in MET cannot rise to dangerous levels. Draw yourself a 3-phase supply system and all will become clear. The best thing every time - switch everything off till you know its safe.

Scary story, Nick. Thanks for sharing.

@6:09 51.9Hz not right either!! I was a very green spark when I went out to a house with a dodgy supply cable and spent several hours scratching my head and changing RCCBs to no avail

I used to do the electricians side of things for emergency callouts for a subsection of the DNO. I once got to a callout where 3 properties had burned down after a neutral fault caused the main fuse in a customers house to blow. He had left his petrol strimmer up against his DB and it had caused the fire. Last I heard his insurance had refused to payout for any of the damage..

When the PEN failed one of the phases was probably intermittently making contact to the downstream PEN giving you 400V, the 100V would be from a floating PEN, unequal load on the phases causes a voltage imbalance causing the virtual earth point to drift towards the phase with the highest load.

Old faults engineer for DNO, neutral fault mate. Been on loads over the years, you should always drop the earth too, as all their pipe work would have been live too. DNO should also have completed a full wiring check prior to energising. Also most smart meters blow up too. The voltage has come from the live touching the neutral in the joint.

IIRC, if everything would be in sync over the three phases, it balances itself, you don't need a neutral. Think electric engine, electric radiator, stove (I live in three phase to all houses-land), but as soon as you have an unsynchronized load and the neutral comes lose, shit starts going south real fast since the phases start pulling differently. We had this happen here when the DNO (as you call them) change electric meters in people's houses and forget to tighten the neutral properly.

What a cool situation to witness. Scary at the time but how informative to see how the other half work.

Happens more than you would think... i work for a firm that repairs the internal damage in the property on behalf of the dno after these neutral faults

Separate hearsay I've also heard (a USA video) is that on single single phase lines with loss of neutral you can also get boilers refusing to operate because the flame detector circuit gets confused by the neutral/earth voltages. It was indicated that the flame detector looks at deliberate 'leakage' currents through the flame to the boiler metalwork (earthed), expecting a return though the neutral bonding, but is confused by all the other currents using the path when the pilot light is started. Classic plumbers vs electrician territory!

Really interesting information thanks for sharing. Nick⚡️👊

If you think back to an ac waveform the neutral is in the middle at 0v when you have a bad connection or no connection the 0v point will either be missing or it will float up and down with the waveform the houses on the phase with the heighest load will get lower volts but push the volts up on the other phases. Also has weird effects on electric motors that can push the volts high.

That's mad 😮😮😮 glad everyone was ok, fair play to WP for getting out to you so quickly 🙌

Had something similar at home a few years ago - lights bright, then dim... then some of the kit in my music studio started to get fried. I grabbed a tester and found had nearly 400V coming out of a kitchen socket!

9 fully charged Unilites… well that amounted to about a hours worth of light between them all…😂

I have seen this once before, i live in the netherland, the neutral wire under the meter was loose, the result was 400v on the entire hous circuit, here whe have neutral and earth seperated, most homes have an earth pin.

It's National Grid Electricity Distribution now in east and west midlands, south west and South Wales. UKPN cover the east/south east, SSE cover the middle bit of the south. ENW cover the north west, NPG cover yorkshire and north east and finally Spen cover Mersey. But all you need to remember is the phone number "105" which is the free emergency number for the whole of England and Wales and it'll connect you with the right people for your area

On residential feeds, they operate on at minimum a 3 wire single phase system but iirc the UK's grid is predominantly 3 phase with one leg feeding sections of a residential. Whenever there's a load imbalance between L1 and L2, the difference gets run through the Neutral which results in no potential variations at all. You'll still see 230v (or 120v in the case of an American grid) at the wall. If you lose that neutral though, as the circuits will still be commoned together at their tie point, what you end up with is whatever load is on those two live wires is now going to be in series. Current will flow from (let's say) L1 and return at L2 instead of going from L1 to Neutral or L2 to neutral. If you've ever messed with different wattage lamps in series you'll know a lot of the time, the higher wattage lamp ends up going dim but the lower wattage one will go super bright. This exact same phenomena occurs when you break a neutral on a 3 wire single phase or a full-blown 3 phase system and the current isn't perfectly balanced across L1 and L2 (and L3 in the case of 3 phase) but because the max potential on 2 wire single and 3 phase can be north of double the line voltage between Lx to N this means you will see some gnarly voltage spikes at the least loaded leg. Here's a really neat demonstration of this exact thing happening. kzfaq.info/get/bejne/jMiPZsZ23JnZqHU.html

I'm in another country where we do a 'Multiple-Earth-Neutral' thing (every main board has a bond between Neutral and Earth, as well as the neutral at the transformer). We had a several hours outage while the nearby 11kv was repaired - a lightening strike set fire to the pole!. That didn't kill our power - the cross-arm burning through did. Well, a crew comes out a chops the burned top of the pole fits a new cross arm, reattaches everything and turns the power back on. Our house comes back up - the electronics (computers, router, etc) all come on. My wife comes in and says her bedside lamp is dim. This is the last incandescent lamp in the house. Break out the test lamps - they are dim in a powerpoint. Break out the multi-meter - we have 120v instead of 230. The consumer electronics all have 'universal' switched mode power supplies, the LED lamps all have current drivers. The fridge pretty is new so has a variable speed electronic drive compressor, so everything pretty much appeared to work fine. It's quite possible neighbours on another phase were getting 350v instead of 240. That could have been upsetting. :-) It was late, the supply people had an active outage on their website, so we just turned everything off and went to bed. We had 240v again in the morning.

I too had a customer that complained about lights being very dim & electronic devices making strange noises, i tested the incoming supply & was reading 50v !! A fault in the road apparently. Another job i just left rang up & said " we have no power!! What have you done ? " i naturally panicked, shot over there & everything was dead.. after briefly scratching my head i discovered they had a power cut 20 mins after me leaving their property.. phew.... what a relief...

I think the issue you had was a phase to neutral fault. The house with a low voltage is on the phase that shorted. The voltage sagged as you effectively have a voltage divider. The houses with high voltage were on one of the other phases. The neutral being shorted to a phase at 120 degrees gets you approaching 400V across L to N as the neutral is now acting like a phase conductor.

Brilliant vid Nick with some great replies. Every day’s a learning day!! I know exactly how sick you must have felt though. I haven’t had that but I did have a coincidental power cut 15mins after I’d completed a domestic CU upgrade. As I was cleaning up the whole street went into darkness, and for those 5mins you’re in total blind panic mode convinced it’s you! 😂 Interestingly a customer of mine told me the other day they were on their 3rd boiler PCB replacement. It’s a fairly rural property and I’m wondering if I should visit to take some readings - perhaps their issue also lies under the road!

Happened to us a few months ago, our supply dropped to approx 100v, elsewhere in the village voltage had risen to the high 300s causing tvs etc to fail. turned out to be a PEN fault, householders having to argue over compensation for damaged equipment with DNO saying claim off your own insurance.

Good episode Nick. You could get the cardboard classroom out (whiteboard) and draw some stuff on it to show how the fault affects the houses too.

Broken neutral on the joint allowing load to flow between phases-after all the street is fed from a 415V 3 phase transformer,it is only the neutral that gives 240V between line and neutral

That sounds fun. Never had a PEN fault but I have had a Line fault on a 3PH. It was in a bakery and I got called out for a mulfuntioning prover. L-N voltage for L1 and L2 were normal but L3 showed only around 140v fluctuating. Called western power and within a couple of hours of testing and faffing - they'd rigged up a huge generator outside and bypassed the grid. They were running on that gen for about 2 weeks before WP finally tracked down the problem in the road. Fun

Quite happy with the talkie format Nick.Hopefully all three houses, know who their favourite spark is...

If i were the occupants of those houses i'd be sending all the sparky and appliance bills to the power provider, that's unacceptable.

Open circuit neutral on a three phase supply - one phase to each of yuor three houses. I had exactly this issue ironically at the CEGB grid control centre Park Street SE1 back in the 1980's. Called out to smke coming from one of their three computers. One fed with getting on for 400 v the othera low. With the neutral floating the voltages on the individual phase becomes dependant on the load on each. Well done for your prompt acction.

Had a three phase joint box on top of a pole next to a small block of flats. Got called out to power outages and non working boilers and appliances in 3 different flats. Odd. Turns out the dno joint box was full of water and the problems had come down the line into the flats. Caused some very strange faults and dangerous live neutrals and consequently on the earth.

That was an open neutral on a 3 phase main supply in the street junction. If 3 houses were each running on different phases a phantom neutral is created at the point where all houses have their neutral connected together, even if this common connection is open to the incoming main 3 phase supply. All works fine as long as each house uses the same amount of power from their respective phase, however if one or two houses use less or more power the potential on this phantom neutral will shift accordingly, thus explaining your varying voltages...

If in doubt ring the DNO out, they won't charge you unless it's obvious you've done something like cut through a cable or tampering with the cut out.

Crazy voltages are confusing which is why checklists and training are your fallbacks. Street wiring can be iffy.

An honest video, had something similar years ago out side our house, the DNO engineers said one phase had completely grounded and the remaining two were still working although one was less than 200v, the other normal one was pulsing, IIRC because it was getting a partial ground to earth on its neutral. One very large hole later and two neighbours set up with a temp feed from the street light circuit, while the work went on over a couple of days and all good. Cant help wondering if it had anything to do with our local transformer in our road literally blowing up a few years earlier.

5:57 that's it you have the answer. There was an (big) issue with the cable supply outside propertiess, short-circuit or something else .. that one of the house, be it in the middle, had voltage between 2 lines of a three phase instead of single phase to neutral. Neutral lost. Neutral combined (touching) with one of the other phases but not going back to the transformer... anything but not great and beauty at all...

I enjoyed this new style of content personally. Well done buddy

In case of confusion… Western Power Distribution (the DNO) are now called National Grid Electricity Distribution. Just to guarantee you get them confused with National Grid who run the grid…

Crazy fault that! Great work being so thorough 👌

Lost an incoming neutral at a fiber converter/ip site in Nottingham, walked in to the data centre, all equipment (ups) on batteries with magic smoke pouring out all the old flouro light fittings and oil pissing out the oil filled radiators in the common areas. Incomer off, generator started fire brigade, Northen Grid & site owner called. Long night swapping power supplies and VFD’s all cooked. UPS failed to bypass 💣

Some years ago we had a broken neutral on the overhead cable close to the substation feeding our house. Measured over 300 volts at a socket. Called SSE Power Distribution and they came out. Told me that they had checked at the substation and it was all fine, must be a fault in my installation. Asked them to check at my meter as I thought it was a missing neutral Which they did. Technicians eyes nearly popped out of their sockets. They checked and found the broken neutral at the top of the pole.

Id say each house was on separate phases or at least one was. What commonly happens is the neutral blows open either from high resistance or arcing to a phase, the uk system is similar to what we run here in NZ one big transformer usually 100KVA to 500KVa at 3 phase 415/230 that then is fed into cables in the ground or powerlines overhead then parodically the feeds for the houses are taken off and to balance the load say if there are six feeds been taken off red phase will have 2 feeds connected, white 2 feeds taken off , Blue phase will have 2 feeds taken off. And the neutral retuning to the transformer only carries the imbalance current or earth fault current . in the situation of three houses or in your cases 1 house open N/E and the other two with joined but not connected to the main neutral who ever has the smallest load connected gets the highest voltage and who ever has the biggest load gets the lowest voltage the ratio will change depending on how many alternative return paths (gas/water/earth electrode) there are and how many houses are been affected.

Dropped neutral faults are sadly becoming more and more common with PME we're getting it a lot on the south coast (surrey/sussex/kent) with UK Power Networks where the old 1940s/1950s cables haven't been replaced and are essentially dissolving and rusting away. Often the first things to go are the boiler PCB's and it's fairly normal to have a call and find out that recently a neighbour or two has got an EV and the fault has appeared after that. This is why Gas Engineers exams and refresher courses (also included in the GasSafe magazine) advise testing incoming gas pipes for stray voltage (with a death stick of all things) before any work is carried out due to the bonded supplies becoming live as they're acting as the neutral.

I fitted a washing machine for a customer many years ago and had to cut off the plug to feed the cable through cupboards to the socket, as soon as I plugged the washing machine in all the lights went off. In a panic I thought I'd screwed up, but as I looked outside the front door, the whole street was off, panic over! 😁😁

Got a call out for something just like this. Neutral connection failed at the transformer. 80 houses or so affected. Lots of blown heat pumps, smoke alarms and fridges. A few houses had power points and appliances catch fire.

I had similar,customer rang and said lights have been flashing since I worked there,I knew it wasn't anything I had done as I had split tails and installed a sub board with the new circuits I had installed.they sent a video of the lights flashing and crackling noise,couldn't believe what I saw...called straight out,tested at the board and there was no neutral,called western power out and it was a loose neutral connection on the overhead post and it had been arcing.

So interesting from a techie point of view. Glad you got it sorted and WP handled it well. Great to see good responses in the comments!

I was called back to work on a Saturday night during heavy rainstorm. Building across the street lost power. The other electrician told me the apprentice to pump a 3,000 amp tripped breaker that feed a 240 to 4,160 volt transformer. Don't know what scared me more the extra loud bang from the dead short tripping g out the 3,000 amp breaker or the switchgear room shaking for a second or two. The switchgear room was located 25' off the ground on six concrete pillars. Was lucky to find the High voltage wire inside a large mogul LB was shorted and placed tape around it then layers if rubber until we could perform a better repair. Also blow up a one piece IGBT for a,150 HP Motor. Had the drive cover closed and screws tight but still got a noise that sounded like a cannon going off. Also had produced a cloud if smoke.

Had kid of the same thing part of a church hall nothing running getting a reading of 240 then plug a kettle in it was pulling it down to abt 180v seemed to only be on the yellow phase turned out it was the joint out in street was braking down scary stuff 👍

A few years back, we had an intermittent issue where, under load (so usually when cooking dinner) the voltage would drop, lights would start flicking etc. I had some of those TFLink wifi controlled plug things (so Alexa could turn on a few lights) which happened to record voltages, so I could see that the voltage was dropping as low as 160v when we had the flickering. We called UKPN, someone was out within an hour, could see an intermittent fault on the neutral which actually failed completely while he was there. They had to dig up the street and rejoint the supply cable It had somehow degraded. We were at the end of a feed from a substation so thankfully our neighbours weren't affected! They had us back on about 5-6 hours after reporting it, so really can't complain. Scary stuff though! I did wonder if I had caused it pulling out a load of dodgy DIY electrics I had found (we had only recently moved in!)

My life for years working with a DNO, simple explanation usually a lost neutral upstream of these 3 houses. The return neutral normally in one house goes back to the common neutral point of the three houses but as there is actually no main neutral because of the fault ,the voltage ( phase 1 say ) is seen in house 2 ( on phase 2) on the neutral so you see two phases across the supply. ( and the bigger the load, say a 8 kw shower the larger the voltage up to 400v) If one of the houses is on the same phase as another you see no voltage across the supply but the phase and neutral are still live to real earth so can be deadly . This is the reason why the new regulations are now talking about an earth spike to help reduce this ( rare ) issue. I used to get whole streets with this problem and rushed to the local substation to drop supplies pronto.

Any damage caused by the supply to the house should usually be insurance and liability with the electrical supply company that laid the cables. They already give you beef if you touch anything between the road and the first fuse they slap in the house. Speaking of which, why aren't there power quality components on boards that can trip during overvoltage/undervoltage events? So much damage could be avoided if they just put extra smarts in that first joint they are so draconian about protecting.

No stories like that from me. Closest I got was new install testing on a massive renovation and the power went out. Took 10 min to realise that the noise digger engine has stopped and outside smelled of burnt metal. Ground workers did the classic trenching a new wall. Digger bucket through dno supply.

I'd guess that arcing and the load inductance would also cause high voltage spikes. That 400v you were measuring probably wasn't a regular sine wave. It was probably a highly distorted sine wave with high voltage spikes all over it.

Here is an issue I saw in my own house a while ago, woke up, lights all worked (All LED), but TV and other appliances kept going on and off, when I got the MFT out I could see Voltage was fluctuating all over the place and there was no continuity on a Zs reading (Although could have been due to fluctuating voltage)... My conclusion was that the cable was completely disconnected and as it was a bright sunny day the solar panels were feeding electricity back into the cable but obviously could not cope with everyone's current so was just jumping up and down as peoples appliances went on and off, everyone in the local area reported same issue.. I turned my consumer unit off and disconnected as many loads as I could as it was TNC-S if anything went up the neutral it would be connected thus to earth, maybe overkill but just incase..

Lost PME neutral happens more often than you think, and can cause voltages to rise above statutory limits. It is actually classed as a significant incident where the DNO must report to the HSE under ESQCR regulations.

Well explained Mr x do 😊

See, 12/24v cables don't scare me, even supplied by a car bettery. I don't get scared by the 220v 1.5mil cables for light. 2.5 for the sockets are kinda iffy. The 10 cable for showers/ovens is spooky but still safe because main board. The main board is getting scary, but there's always that main supply fuse. Now. The cable after that is hella scary. And then we go to the 3 phase 400V 1000A industrial stuff - now that's terror.

thats what i thought neutral when you said the lights were dimming lose neutral down stream and the voltage was playing up

Good work Nick, I wonder how almost 400v would have affected a EV whilst on charge especially those chargers without PEN fault protection. Lots of sparks say they don’t like PME supplies because of loss of neutral and then losing the Earth and they think all houses should be TT, maybe it’s the way forward as we use 30ma RCD or RCBO’s for all circuits these days anyway.

Well done, Nick. Fantastic job!! I've got problems in my street with cables deteriorating. Had the dno out at least 10 times last year for power cuts. Adventually, they are replacing the incoming supply for 3+ Streets around me and mine.

Very simple, its called a floating neutral. If the neutral of the 3 phase supply to the street becomes disconnected, the house with the highest load goes to the lowest voltage, the house with the lightest load goes high, potentially up to phase to phase voltage of 415. Its a common scenario on any 3 phase supply and the results are devastating. You could check neutral to ground voltage to verify this, any more than a couple of volts and you have problems. Have seen this many times with 3 phase extension leads and its the reason in Australia that the plugs and sockets have double screws on them just like the earth has. The exact same thing happens in the US on their split phase/2 phase residential supplies. if the neutral in the street or board becomes lose, half their consumer unit droop below 120, the other half goes up by the same amount. Plug a large load onto one side and the equipment on the other side explodes.

Makes you wonder if there are better ways of doing things if cost weren’t an issue. For example something like CityFibre have terminal boxes at pavement/property boundary for their fibre connections which then goes to the house. Could DNO have a similar accessible terminal box at property boundary with a small device to monitor lines and voltage. Allow for an automatic disconnect outside property if a N/E fault or over voltage.

Had this happen at work, lost neutral caused by digger down the road blew up contactors all over site costing thousands.