A very worthwhile test. I've always been a bit sceptical about the ability of a single core being able to induce a significant current in the surrounding metalwork. This appears to be a myth that goes back a long way, and I wonder if it is an issue with more industrial supplies (I'm not so sure) or if it was a myth born from an excuse for overloaded cables. It also suggests that the people who write the regulations haven't actually tested it. But then, that's not really a surprise for the office-seat electricians at the IET. I wonder if something like a bush or run of conduit would compound the effect though, even if the heating effect wasn't an issue it might effectively act as a slight choke and soften current transients.
Super interesting, thank you! As a spark, it gets drilled into you to never bring conductors on the same circuit through separate holes in metal enclosures as if it would burst in to flames immediately. It’s one of those things you just don’t do. Seeing an actual test and seeing the minimal affect is surprising to say the least. Don’t get me wrong, I’m not about to start bringing my cables into separate holes now, but to see the minimal affect from eddies on a domestic board is a surprise. Cheers!
Interesting piece on eddy currents, not everyone would have thought about this and guaranteed youll see some consumer units set up like this in the near future! Good vid JW
Came across a 3 phase meter in a factory unit connected with 25mm tails which came through individual holes in a metal trunking under the meter. The trunking was running very warm!
Was it warm because of the cables being warm or from eddy currents? There is an armoured cable feeding an overhead supply up the road from me. It's running more load than usual as they're backfeeding another section on it, and it gets warm due to the load.
''rather disappointing test'' Well this guy appears as professional as you can get... but deep down each and every single guy... unless shit blows up or goes on fire, it pretty much means it was a disappointing test!
The answer with eddy currents and the heating effect is to make a cut between the two holes at the shortest distance. In Australia incoming single core conductors are quite the norm. I have known the local installation inspector to fail a job as there was no cut between the holes.
pirate69s I always think cutting a thin slot is rather pointless as it would only take one strand of swarf or metal filing to close the slot. Depending on the installation I have used aluminium gland plates (when glanding single core swa’s) or Pacylene for large tri rated single core tails. Aluminium is surprisingly difficult to drill with hole saws though!
I came across this situation in a school in Essex in the late 80's. Working for myself. Big old style single phase Federal DB fed via a pair of single 35mm bare copper Pyros, Live Pyro in one hole of trunking and Neutral in other hole. Noticed an annoying low buzz one day from up high where cables where pinned to wall, assumed it was 1960 style fluorescent tube in cleaners cupboard adjacent to cables. Investigated one day and was going to change the fitting and discovered the buzz actually coming from trunking between Pyro glands and it was actually hot, you could hold your finger on it but neverless hot. The paint on the old trunking had flaked at this point. I mentioned it to site manager as he was responsible for all maintenance and suggested it needs attending to and why, I even put a quote in. Never got asked back to the school, I heard in the wholesalers a few weeks later that they got some local cowboy in to check it and he said it was fine. The cowboy was a husband of a school cleaner who worked in a local factory I also heard. I hoped it would start a fire in the cleaners cupboard as they stock pile flammable goods in there, and I advised them against that, all the same the school didn't burn down and it is probably still there keeping the cupboard warm and dry to this day. Watching this vid brought it all back, and BTW it turned out the maintenance manager thought I was pulling his plonker, blinding him with bullshit to make me extra work and money ffs. How do these facking dinosaurs get into these building manager positions in the first place. Sorry about the rant but I feel better now!!!
How about a single wire through a metal conduit. Aus standards prohibit doing so, requiring the full current to return via the same run through the metal, be it a switched live, other phases or neutral wire. Eddy currents are the issue like this video, but they'd have much more of an effect in an ideal conductive long cylinder. Could you do a video please?
I'm not sure "eddy current" is the correct term. That wiring fault actually creates an accidental transformer and might be capable of inducing touchable voltage if the loop of conduit is broken at one point. It would still be an interesting experiment.
Very interesting test John. I suspect that the 2C increase in temperature might actually be down to heat transfer as the cables warm as much as from eddy currents, especially when you consider their close proximity to the temp probe..
Me too. My estimate was that length of 25mm^2 cable at 120 amps dissipates about 8 watts. The eddy current theory is a myth. You get it in transformer cores, as they have hundreds of windings designed to induce a very large, alternating magnetic field, and that does induce eddy currents in the core which is there to maximise the magnetic field. Two wires running at right angles through a thing bit of steel aren't going to have anything like the same effect.
Most of John's output is excellent but this one is, shall we say, not so hot. For a scientific result, the test could be repeated with a twin cable gland and the rise measured. I suspect the difference will be tiny if any.
The geometry seems wrong for inducing eddy currents. The magnetic field is circling the conductor in the plane of the side of the box. However, the induced voltage goes around the magnetic field lines, so any induced current would be following in a plane perpendicular to the side of the box. Essentially you've recreated a laminated core with just a single lamination. As laid out, the back side of the box is more likely to see eddy currents. A flat piece of metal between and parallel to the conductors would maximize the effect.
Eddie Currents was the lead singer of that 1950’s rock’n’roll band DC/AC. They never went far. Their manager thought it had something to do with the band’s name, but nobody could put their finger on what they should change it to.
I don't understand how any well constructed tests' result could be disappointing unless you had a cherished prevous opinion or theory you were trying to substantiate. This test supports my theory that code authorities sometimes make codes based upon preconceptions without doing any calculations or tests, and/or fail to modify them when experience and testing shows those codes are overly conservative. In the US, regional codes are as often based on union electricians preferences and are inflexibly enforced until experience from regions without trade unions demonstrates that other materials and techniques are safe and effective.
i know im 5 years to late but not sure this test is well constructed in order to be real life an earth needs to be present as if you look at any transformer diagram . in order to induce induction one pole\side needs to be greater then the other ie line (25mm) in one hole neutral and earth in another hole (25mm + 16mm) this would gave true readings
@@gasmonkey7430 Wrong. His test 'failed' because the case is of very thin sheet-metal. Similar to she core layers in a transformator which are so thin for the same purpose, not to get hot. What he has built is the first half of a current transformer. Anyway, interesting.
I'm in my 60s now, but, years ago we were taught that if you had to go through separate holes you had to cut a slot between them with a hacksaw blade? Thanks for the video.
I wonder if a thicker enclosure like the old cast switchfuses would heat up more? I remember reading it was recommended to cut a slot between the two holes to stop any eddy currents.
What problem we have is the magnetic flux will create an electrical eddy current and induce heating of the chassis of the "consumer unit", or "breaker panel", "sub panel" or whatever they are called in whichever local. We sometimes use single conductor mineral insulated conductors here in the USA. Usually we have three phases (120 deg lead/lag) and a neutral. These single conductor MI cables are usually 50 amps and greater, so the probability for heating is slightly greater. Usually we will cut slots into the metal between all the holes involved. I like seeing the old UK mains systems again.
Interesting, I was expecting a larger increase, given the dire warnings that used to be given. I wonder if in a real world situation, if the high frequency harmonics produced by large amounts of switching power supplies these days may cause this to be a much more significant problem in commercial installations (thinking of 400-1600 amp commercial supplies with IT equipment hooked up). I know these harmonics can cause problems with neutral overheating on 3ph supplies, maybe the extra eddy current loss at higher frequencies would cause issues too?
Absolutely fascinating, I am well aware of eddy currents but it never occurred to me in this scenario. I would actually have expected the heating to take place in the rear panel of that box where it would be in the field of the loop. Possibly in the cover too if it had been fitted...
Regs state the both conductors must go through same hole to cancel eddy currents this is more noticeable when two separate conduits are used to pass one conductor down each conduit and act as a transformer, eddy currents will start to flow up one conduct and down the other, now the conduct has a brass bush at the end, this is not always a good connection and acts as a resistor, and as the eddy current flows thorough this joint it will get warm and as time goes by this joint will corrode and the resistance will get greater and therefore the heating effect and so and so on until you have nice warm fire.
I'm sure that in high current situations, it can cause overheating. However, despite it not being able to overheat within 125A, any added heat to the system is not helpful when it comes to dissipating the normal system heat. Either way it's to be avoided.
I would be interested seeing you create a true shorted turn. I once did this accidentally when I installed a toroid transformer in a metal box. The box lid got squashed and there was quite a bang.
When I first learned of this rule, the situation was using a twisted multi cable (like a drop cable to your house) run on both the live and neutral. Where the two cables passed through a metal plate, there had to be 1 live wire and 1 neutral wire in each hole. Basically, untwisted and then paired together, as both cables wouldn't fit in a single hole. I'm wondering if it's the spacing between the holes that makes the difference. Like, instead of looping the cable (as in this test) through adjacent holes, but in one hole and out a hole further away or on the other side of the box. If this is the case, I can see choosing the simple instructions of using one of each per hole. It could be quite cumbersome to have to calculate a safe spacing. And we already get plenty of shady wiring. I have only used 6 AWG wire once. Most of my experience is 12 or smaller. I know that I wouldn't be comfortable doing these tests, so ... Thank you!!
Great test John. I would like to see just the one line incase there is a cancellation effect due to the propagation of the magnetic field. But as others have said you do get the feeling that the regs are sometimes a bit regs for regs sake and not as close to real world examples as they could be.
The way you have it rigged John means that the current in the wires at the point they pass through the hole will be in direct opposition so the resultant combined magnetic field would be much reduced. What happens if you only have a single wire passing through one hole - more representative of installation where tails are inappropriately (widely) separated?
Nice experiment, but I will suggest an improvement if I may. Your temperature probe is going to pick up the wire itself heating up inevitably. Let's assume that the metal box acts as a choke on the wire and adds imaginary resistance to it. Here's what to do: Run your constant power supply through your wire in open air (no box) and measure the voltage drop on it as accurately as possible. Then install it in the box, reattaching the ends as faithfully as possible. Measure the voltage drop again. The difference in the voltage drops can be used to calculate the impedance of the choke and the heating power in the sheet metal.
Not necessarily because the metal box dissipates heat more quickly as its temperature increases (and so the temperature difference between it and the surroundings becomes larger). In fact, it's likely that the 2 degree increase was caused by the resistance of the wires themselves -- or a good portion of it was anyway.
That's to make the erroneous assumption that temperature increase linearly over time. The answer to that is no they don't. An equilibrium will be reached when the heat being generates matches that being conducted away. If that was ever going to get to dangerous temperatures, it would have become obvious after 5 minutes as the temperature would have climbed a lot faster. As it is, a quick calculation on the length of that 25mm^2 cabling within the box (I estimate about 30-40cm) would dissipate about 4-5 Watts. It would not surprise me if the great majority of the increase in temperature was from the slightly warmed air rising. I suspect if the temperature of the wire was checked it would have increased by a great deal more than 2C just from resistive warming.
Great test! I have always wondered what this would be in practice. Though I bet there are some variations on this test that would cause a greater heating effect. Proximity of cables, thermal mass of the case etc. I guess there is a point at which the case cannot dissipate the heat generated causing the conductors insulation to break down and then short. Excellent job 👍🏻
i was involved once with a television transmitter installation where they ran 3phase power to the main disconnect box using three separate conduits, one phase in each conduit . Those got red hot! Granted it was a hundred amps and the metal separating the conductors was not just the metal box, but was a length of about 10 feet of conduit; but that situation was an example of the same effect. The conduit / metal box created the core of a transformer. The solution was to run three separate smaller size wires in each of the three conduits so that each conduit contained all three phases adding up to the required wire size for the current draw.l
A little late for a reply. The condition you describe is because the metal conduit was connected at both ends. In industry if you had large single core armoured cables carrying several hundred amps, the gland plate at one end was always insulated to stop Eddie currents circulating around the armouring or conduit
It's interesting as the electromagnetic affect consideration now appears on the schedule of tests for an electrical instalation. far more worrying that we now have to use metal consumer units on a TT earth system . It was once considered a no no to put mains tails with no back RCD protection into a metal enclosure but now it's fine with a plastic stuff in gland . load of tosh in my view. love your methodical uploads ,as interesting as Big clive .
As a sparky doing remedials ,I have had to reroute cabling though the same hole (3ph) which has been running perfectly ok for years, your findings seem to dispel any reason for doing this.Maybe it's just good practise?
Under the 16th edition regs it says "conductors shall not be surrounded individually by ferrous material or that provision shall be made to prevent eddy (induced) currents." So its not saying NO full stop, its suggesting there may be a problem by doing this so if an older existing installation which was installed under those older regulations is operating normally there would be no need to change the cable routing into the enclosure.
Hi jw on metal c.u dose it matter if the earth passes through a different hole to the live and neutral or is it okay as long as the live and neutral go through the same hole thanks
Good vid, not to ask a silly question but would the current induced in the metal be significant enough to generate a shock or be picked up through a tester?
One might wonder whether the 2C change was as much due to environmental change? In any event as any induced current would be in the steel case, one would expect that to be the subject of any increase in temperature, not the supply cable.
Are you using an arc welder off screen to produce this current? If so, does it have a rectifier in it? I wouldn't expect pulsed DC to give you the same Eddy current effect as true AC. Really interesting test, I'd be curious to see your whole test setup.
@@jwflame thanks for the info! I guess it makes sense that a flat steel plate wouldn't get much by way of Eddy currents, it's how we design transformer laminations after all!
Interesting, I suspect you could get a better induction heating effect by putting a few turns through the two holes, although I suspect that even one or two turns would not produce enough effect to raise the temperature significantly. Half a turn it seems is not nearly enough to have a measurable effect. I can see why someone might be daft enough to do this, to "keep the excess wire neat", in the same way that people operate large coiled mains extension cables still coiled up on the reel (to keep them neat) and wonder why they start to cook after prolonged use.
Not sure why did you expect significant eddy currents resulting from a couple of wires going perpendicularly through a thin metal plate. You mentioned transformer core lamination design, well it is almost exactly the same scenario here with two notable exceptions: 1. it is like just a single platter of a transformer core rather than the whole bunch of them; 2. it is wire going through the plate once rather winding around it. All in all eddy currents at 50Hz should be expected to be insignificant in those circumstances and so they proved to be.
I am curious. Doesn't the impedance of an inductor occur within the copper itself? Would this not theoretically directly reduce the rated current carrying capabilities of the wire, however small that reduction might be? You should measure the effective henry rating of the fuse box acting as an inductor in a setup like this.
Interesting, if i had to bring the tails into 2 holes I'd cut a line through the bridge thus making it one hole. I really think we've taken a step backwards with the regs here as there are lots of plastics that don't support combustion
glenwoofit As Wylex now unhelpfully put a single 32mm hole the centre of the bottom of their metal CUs with 20mm ones either side, I was going to do exactly that here (cut a slot between two of them) so the meter tails can enter neatly in line with the main switch. But I wasn't expecting the eddy current heating to be so small.
i have first hand experience of this and have found in every case where heating of the enclosure occurred both the neutral and earth were taken through different holes as each other and line or both earth and neutral in same hole but line in different one. in one case where all 3 phases neutral and earth had been taken through different holes. the supply to the hotel would cut off for 30 seconds then come back. this only stopped when i cut slots between each hole. cant begin to explain how or why but i was called after 2 years of this happening and the only fault i could find was supply taken through different holes and it stopped when i slotted the holes.
I am going to do what you shouldn't, and that is comment on the video before I've watched it all the way through. However, there's a reason. That's because, before you even do this test, I'm going to predict that there will be no significant heating caused by eddy currents induced by the magnetic fields, even if you put 100 amps AC through the thing. Transformers (and induction hobs) have got large numbers of windings designed to generate powerful magnetic fields. A couple of parallel wires a few centimetres apart will not generate enough field to induce large current flows. So, not I will watch the rest of the video and see if my prediction comes true of not. **** update **** My suspicions were confirmed. I would also suspect that the slight warming that was seen at 125 amps was largely down to convection currents from that loop of wiring. Assuming that it's about 25cm long (or about 10 inches), then that length of 25mm^2 cable will have a resistance of 0.0005525 ohms (which doesn't sound like much). However, power resistive losses are resistance times current squared. 0.0005525 x 125 x 125 = 8.6 watts. I think that putting a 9 watt heater under that thin bit of steel could easily account for the great majority of the warming effect. Of course, at 25 amps there will only be about one-third of a watt, so that would be negligible. nb. high powered cables running parallel to steel panels would induce more current, but at right-angles it's going to be negligible. I wonder how many of those stories about overheating panels are more down to resistive losses (including from poorly made terminations) than induction currents.
this test is floored you said your self about transformers just look at a simply diagram of one and you will see one side of the transformer is larger so putting one cable through a hole and out another wont give a true result you would need to run an earth cable with the neutral or in its own hole to lower the resistance and unbalance the circuit then test.
Like, jolly-good show. Per chance you could do a video in which you operate multiple kettles, all plugged into one multi-socket mains-extension lead. Cheers!
Take a couple of loops around it through the holes, with an iron bar down the middle of the loops. it wont do much either but you may find your metallic tools.
My impression (as a physicist, not a working electrician) is that the expected heating is not from eddy currents (the thickness of the metal limits those severely) but from the magnetic field itself and the resulting hysteresis (iron) losses. Whatever the source, it is generally not significant except at much higher currents than you tested with or with more substantial (thicker) ferrous metal plates. I am having trouble thinking of a simple experiment to prove one way or the other. I suppose that using a ferrite or other composite material which was magnetically active but not electrically conductive might do the trick.
If a significant heating effect was observed then the test could be repeated with a non ferrous metal such as aluminium. If the heating is caused by eddy currents then it should still occur but if it's due to magnetic losses then it should no longer be present. I personally can't see why there should be any eddy currents at all because the lines of magnetic field will occur in the plane of the metal sheet so any eddy currents would have to be perpendicular to the sheet and there isn't any perpendicular path for them to flow in. The section of cable in this test that's laid flat on the metal case is much more likely to induce eddy currents but even then they will be small because the magnetic field in the air surrounding a cable is itself small due to the low permeability of air.
What about the frequency? If the power supply had a lot of noise, then I presume there would be more heating. Could be interesting to run the test at 500hz, 5000 hz etc.
John is this actually a fair test? 120A x 50v = 6000vA the aprox output from your welder. 100A at 230v = 23000vA the aprox output from a fully loaded consumer unit I could be wrong but suspect the heating effect would be higher. I do agree I have seen metal consumer units with tails in separate holes with no noticeable heating present.
That's entirely irrelevant. All that matters with eddy currents is the induced magnetic field and the only thing that matters is the current. The amount of power being dissipated elsewhere doesn't matter in the slightest.
The two conductors would be L&N in a normal consumer unit. The only difference between L&N is the voltage relative to Earth - L 230v, N 0v. Magnetic effects are caused by current, the voltage relative to other parts isn't important. In this case it's the same conductor, but the key point is the current direction is different through each hole.
@jwflame I am aware of this reg but I can't understand why , my thinking was if the L and N are thru different holes the eddy currents can cause a build up of heat over time but if there's no current going thru the earth except in a fault it would only be for a few seconds so wouldn't have time to build up heat.
The more I see of standards outside of the US for electrical the more I think the US is not so backwards. In the US the mains comes in via conduit, it wouldn't be possible for someone to even think of running one wire in one hole and another wire in the other.
Great putting this out there, but the measuring of temperature was not where I saw this test going, the rise could have been down to the transference from the Conductors, or the surrounding air temperature rising over time? Why not do the same test but this time put a Voltmeter attached to the M/C Consumer Unit and the other to an Earth Spike [run a remote Earth Cable] in the Ground, somewhere likely to get a Good return path, now measure the voltage at the start and at each stage of the Test. Mr Spence Eng
Good evening John, May I ask and maybe state, did you post this video as BS7671 Amendment 3 states that in 2016 all CCU which are to be installed have to be metal.
Just wondering, 100 amps at 230 volts Vs 100 amps from a transformer or what ever you used there at maybe Extra low voltage, The mains kilowatts would be much much higher would it make a difference?
They invented the TRANSFORMER! We were taught in trade school if you did this in a metal board ( pass a single conductor through an aperture ) Put a cut between the holes to negate eddy currents Remember guys balance your loads!
I know mains is low frequency ... but now try this with high frequency. You might get more heating, because of the skin effect, which makes the thick metal box become a thin metal box, in respect to where the electrons flow... thus, it would heat up more because of the higher resistance .. or so that is the idea XD
+John Ward i agree with that the heat rising from the cable is what caused the change, however it would have been nice to have seen another meter to read the heat from the cable, a closed box in a not open to the basic elements of nature. i know this wont change the results of what you found here but will be interesting to see how the tempreture will change used normally of just the wiring... a test using a miligauss meter would be interesting to see is someone was to put cable in one hole and then in a hole either side of the unit as a pass through with like mains in then to a shower etc, then to test the induction of all four corners as if its like a transformer.
@@ribblehead02 Fine. Eddy currents are induced in a conductor by changing magnetic fields. The magnetic field induced by a conductor depends on on the amount of current flowing through it. Whether the case is earthed or not makes no difference, nor does the voltage applied across any load. Only the changing current matters. nb. transformers work by having many windings to build up the magnetic field, and mains frequency transformers use iron cores to, for want of a better word, amplify the magnetic flux, and those do have significant heating from eddy currents.
? DC ? The IET is a recent creation formed from the combination of two institutions founded in the late 1800s (Wikipedia). In the practical guide book published by the IIE in the 1970s: a single hole or slotting between holes was recommended. In years past DC distribution and control was widespread. ? Has anyone experience of high amperage DC in single core cables that pass through a steel plate, welding for example ?
My thought too. I'd guess that loop of cable in the box is about 25cm. A bit of calculation on 25cm of 24mm^2 cable with 125 amps running through it shows it dissipates about 8 watts from resistive heating. I think that could easily explain the reason the box warmed up as convection currents would have risen. At 25 amps, then there would have been only about 0.3 watts from that source.
this is something that we used paxoline for in all installations cut a slot and then cut the paxoline and pass the cables together through it, mind you were were talking between 300-600 and more amps loading this is basic 1 st year apprentice training FFS
I saw a dramatic overheating in cables that were feeding a low voltage but high power inductive load all the cable overheated like a living hell until we have then separeted
JW Firstly you videos are very informative. I feel that for the eddy currents just bringing a conductor through the steel enclosure with a load on is not the correct way to test this theory, In normal situations the line and neutral conductor would be entering the enclosure and then the loads placed on these cables would be from inside the enclosure. I was told a story when i was at college many years ago now how a TP+N supply was installed in singles conductors and installed into the DB singly. A 2kw load was placed on an outgoing circuit and the heat after a short while blistered the coating on the DB. Again possibly urban legend. But would it not be an idea to test this theory in a video. Also the 2 deg temp rise was most likely caused but the conductor temp when running a 117amp load. I look forward to your thoughts on this.
+Mark “Marcuscrackus” Everitt How is this setup any different to what you described? What do you think would happen differently to the field lines around the conductors?
I really don''t get this experiment. It appears to me that the net magnetic field on the panel would be 0 since the current at any instant would be in separate directions because the wire is looped in and out of the panel. Magnetic fields would tend to cancel each other. If he had put 2 separate wires through the panel with each wire connected to the load resulting in additive magnetic effect he certainly would see a different outcome.
I don't think you understand the concept of eddie currents, the metal divider (between the 2 entry holes) is in a constantly changing magnetic field, this would see a current flow generated but like the video implies at domestic level this is rarely if ever an issue, the metal splitting the cables apart interupts any cancellation of the magnetic field would occur if the cables went through the same metal opening.
@@jwflame If you tried this again with DC it would confirm conclusively whether the heating effect was due to ohmic effects in the cable or eddy currents in the case. Plus an added bonus of a spark of some significance when you disconnect the supply !
That was quite interesting, apart from putting the wires through separate holes. Whats the go with those tail clamps, as they quite clearly separate the tails inside the enclosure. Or have they already looked into that..?
An enjoyable and well exicuted video, but i cannot stress highly enough the very real problems that eddy currents cause in poorly designed switchboard and cable ladder installations. Eddy current heating typically is only an issue in installations running over 250Amps @ 50 Hz, so whilst your video addresses the (watch makers currents found in domestic consumer units), try the same test with the same consumer unit fitted inside an insulated wall cavity with third order harmonics and a few well loaded RCBO's all adding to the heat rise. I earn a good living fixing these and other problems in 500+ Kva installations, unfortunatly I am usually too busy trying to get the installation back on supply to take videos of the discoloured paint, damaged cable insulation and hellish buzzing noises caused when people go off making iron circuits around unballanced currents after seeing these sorts of dangerous videos.
"....these sorts of dangerous videos." Sorry but how on earth is this video dangerous? What you've described is not what he's showing here is it! What we're looking at is a simple metal consumer unit, in the cold outside air, with circa 30Kva I think? I genuinely found your comment interesting to read, I don't work in your industry but I'm considering a career change and it's interesting to understand what type of work an industrial electrician may do day to day. But this is not a dangerous video because he's not misrepresenting anything. Nowhere does he imply we can all ignore the regulations now and do our own thing. Quite the opposite.
Lets be practical, this isn't aimed at Domestic Households of a 100A or less. I'd imagine if you took an enclosure in a tube or train station, with 25kVf, and the train pulling 2500 kW, I'd imagine a small bit of metal that should of been removed, would get toasted by Eddy Currents. Maybe try this experiment with tin foil :) ?
Great series of videos John So 120A 220v AC and your connecting the most dodgy pair of crock clips without isolating the supply or wearing rubber gloves. Cool. i wanna go. I'm not a great fan of steel consumer units, didn't the London Fire Brigade ban them in the eighties (16 Ed) and now as if by magic they are safe from being a fantastic short circuit to the mains. ummm. Are they the same muppet's who insisted all fire extinguishers should be red so you visually spot the different type in low visibility and hung 1m off the floor so that when you are crawling around on the floor in a smoke filled room to get your last breath you end up knocking a great hunk of steel off the wall onto your head. Thought so.
Myth Busted, in order to prove the effect accurately it would have to be good old 220v supply, i tend not to connect my welder up through the consumer unit - as shown. i guess DCEN means DC so yet another flaw in the experiment. Shame i thought John had stumbled across a method of telling the London fire brigade why we got rid of these things in the first place in favour of slow burning, zero halogen, self extinguishing plastic. In 20 years the rules will go back the other way, so they can charge more money and write another edition of the regs to get us all back on courses.
So rare to see someone test their belief and actually accept it when it doesn't go the way they were expecting. Earns you a lot of trust and respect!
A very worthwhile test. I've always been a bit sceptical about the ability of a single core being able to induce a significant current in the surrounding metalwork. This appears to be a myth that goes back a long way, and I wonder if it is an issue with more industrial supplies (I'm not so sure) or if it was a myth born from an excuse for overloaded cables. It also suggests that the people who write the regulations haven't actually tested it. But then, that's not really a surprise for the office-seat electricians at the IET. I wonder if something like a bush or run of conduit would compound the effect though, even if the heating effect wasn't an issue it might effectively act as a slight choke and soften current transients.
yay I found big Clive here
+bigclivedotcom
more so with three phase supplies, remote metering your see mylar plate bolted into enclosure.
Also contact area minimal
when Big Clive shows up, you know it's about to go down
bigclivedotcom who here read Big Clive's words in your mind as big Clive's voice? I know I did, specially the "I'm not so sure " bit , ha ha ha.
lol
Super interesting, thank you! As a spark, it gets drilled into you to never bring conductors on the same circuit through separate holes in metal enclosures as if it would burst in to flames immediately. It’s one of those things you just don’t do. Seeing an actual test and seeing the minimal affect is surprising to say the least. Don’t get me wrong, I’m not about to start bringing my cables into separate holes now, but to see the minimal affect from eddies on a domestic board is a surprise. Cheers!
Interesting piece on eddy currents, not everyone would have thought about this and guaranteed youll see some consumer units set up like this in the near future! Good vid JW
Great vid as always. Thanks. Just wondering when you are going to bang us out a tune on the old organ!
Came across a 3 phase meter in a factory unit connected with 25mm tails which came through individual holes in a metal trunking under the meter. The trunking was running very warm!
Was it warm because of the cables being warm or from eddy currents?
There is an armoured cable feeding an overhead supply up the road from me. It's running more load than usual as they're backfeeding another section on it, and it gets warm due to the load.
Hi JW... Congratulations on your 1000th subscriber. Please keep your most informative and educational vids coming!
''rather disappointing test''
Well this guy appears as professional as you can get... but deep down each and every single guy... unless shit blows up or goes on fire, it pretty much means it was a disappointing test!
The answer with eddy currents and the heating effect is to make a cut between the two holes at the shortest distance. In Australia incoming single core conductors are quite the norm. I have known the local installation inspector to fail a job as there was no cut between the holes.
pirate69s
I always think cutting a thin slot is rather pointless as it would only take one strand of swarf or metal filing to close the slot. Depending on the installation I have used aluminium gland plates (when glanding single core swa’s) or Pacylene for large tri rated single core tails.
Aluminium is surprisingly difficult to drill with hole saws though!
I came across this situation in a school in Essex in the late 80's. Working for myself. Big old style single phase Federal DB fed via a pair of single 35mm bare copper Pyros, Live Pyro in one hole of trunking and Neutral in other hole. Noticed an annoying low buzz one day from up high where cables where pinned to wall, assumed it was 1960 style fluorescent tube in cleaners cupboard adjacent to cables. Investigated one day and was going to change the fitting and discovered the buzz actually coming from trunking between Pyro glands and it was actually hot, you could hold your finger on it but neverless hot. The paint on the old trunking had flaked at this point. I mentioned it to site manager as he was responsible for all maintenance and suggested it needs attending to and why, I even put a quote in. Never got asked back to the school, I heard in the wholesalers a few weeks later that they got some local cowboy in to check it and he said it was fine. The cowboy was a husband of a school cleaner who worked in a local factory I also heard. I hoped it would start a fire in the cleaners cupboard as they stock pile flammable goods in there, and I advised them against that, all the same the school didn't burn down and it is probably still there keeping the cupboard warm and dry to this day. Watching this vid brought it all back, and BTW it turned out the maintenance manager thought I was pulling his plonker, blinding him with bullshit to make me extra work and money ffs. How do these facking dinosaurs get into these building manager positions in the first place. Sorry about the rant but I feel better now!!!
How about a single wire through a metal conduit. Aus standards prohibit doing so, requiring the full current to return via the same run through the metal, be it a switched live, other phases or neutral wire. Eddy currents are the issue like this video, but they'd have much more of an effect in an ideal conductive long cylinder. Could you do a video please?
I'm not sure "eddy current" is the correct term. That wiring fault actually creates an accidental transformer and might be capable of inducing touchable voltage if the loop of conduit is broken at one point. It would still be an interesting experiment.
Very interesting test John. I suspect that the 2C increase in temperature might actually be down to heat transfer as the cables warm as much as from eddy currents, especially when you consider their close proximity to the temp probe..
Me too. My estimate was that length of 25mm^2 cable at 120 amps dissipates about 8 watts. The eddy current theory is a myth. You get it in transformer cores, as they have hundreds of windings designed to induce a very large, alternating magnetic field, and that does induce eddy currents in the core which is there to maximise the magnetic field. Two wires running at right angles through a thing bit of steel aren't going to have anything like the same effect.
Most of John's output is excellent but this one is, shall we say, not so hot. For a scientific result, the test could be repeated with a twin cable gland and the rise measured. I suspect the difference will be tiny if any.
The geometry seems wrong for inducing eddy currents. The magnetic field is circling the conductor in the plane of the side of the box. However, the induced voltage goes around the magnetic field lines, so any induced current would be following in a plane perpendicular to the side of the box. Essentially you've recreated a laminated core with just a single lamination.
As laid out, the back side of the box is more likely to see eddy currents. A flat piece of metal between and parallel to the conductors would maximize the effect.
Eddie Currents was the lead singer of that 1950’s rock’n’roll band DC/AC. They never went far.
Their manager thought it had something to do with the band’s name, but nobody could put their finger on what they should change it to.
I don't understand how any well constructed tests' result could be disappointing unless you had a cherished prevous opinion or theory you were trying to substantiate.
This test supports my theory that code authorities sometimes make codes based upon preconceptions without doing any calculations or tests, and/or fail to modify them when experience and testing shows those codes are overly conservative.
In the US, regional codes are as often based on union electricians preferences and are inflexibly enforced until experience from regions without trade unions demonstrates that other materials and techniques are safe and effective.
i know im 5 years to late but not sure this test is well constructed in order to be real life an earth needs to be present as if you look at any transformer diagram . in order to induce induction one pole\side needs to be greater then the other ie line (25mm) in one hole neutral and earth in another hole (25mm + 16mm) this would gave true readings
@@gasmonkey7430 Wrong. His test 'failed' because the case is of very thin sheet-metal.
Similar to she core layers in a transformator which are so thin for the same purpose, not to get hot.
What he has built is the first half of a current transformer.
Anyway, interesting.
I'm in my 60s now, but, years ago we were taught that if you had to go through separate holes you had to cut a slot between them with a hacksaw blade?
Thanks for the video.
Best first line in a TH-cam video ever!
I wonder if a thicker enclosure like the old cast switchfuses would heat up more?
I remember reading it was recommended to cut a slot between the two holes to stop any eddy currents.
+heavydiesel I am personally more worried about the electrical impedance from the reflected magnetic fields overheating the copper, not the fuse box.
What problem we have is the magnetic flux will create an electrical eddy current and induce heating of the chassis of the "consumer unit", or "breaker panel", "sub panel" or whatever they are called in whichever local. We sometimes use single conductor mineral insulated conductors here in the USA. Usually we have three phases (120 deg lead/lag) and a neutral. These single conductor MI cables are usually 50 amps and greater, so the probability for heating is slightly greater. Usually we will cut slots into the metal between all the holes involved. I like seeing the old UK mains systems again.
Glad to see the shed was energised via the screw :)
So does this mean the magnetic field generates raisins for me?
Interesting, I was expecting a larger increase, given the dire warnings that used to be given. I wonder if in a real world situation, if the high frequency harmonics produced by large amounts of switching power supplies these days may cause this to be a much more significant problem in commercial installations (thinking of 400-1600 amp commercial supplies with IT equipment hooked up). I know these harmonics can cause problems with neutral overheating on 3ph supplies, maybe the extra eddy current loss at higher frequencies would cause issues too?
Could the two degree increase be due to the proximity of the cables and not eddy currents?
Absolutely fascinating, I am well aware of eddy currents but it never occurred to me in this scenario. I would actually have expected the heating to take place in the rear panel of that box where it would be in the field of the loop. Possibly in the cover too if it had been fitted...
Not a disappointing test at all. It was very practically instructive
Regs state the both conductors must go through same hole to cancel eddy currents this is more noticeable when two separate conduits are used to pass one conductor down each conduit and act as a transformer, eddy currents will start to flow up one conduct and down the other, now the conduct has a brass bush at the end, this is not always a good connection and acts as a resistor, and as the eddy current flows thorough this joint it will get warm and as time goes by this joint will corrode and the resistance will get greater and therefore the heating effect and so and so on until you have nice warm fire.
If you left it for 24 hours though would it keep going up ?
I wonder if the effect would be greater a real load was applied so the sine curve was dirty? Surely this dead short is a best case scenario.
normally one of the wires would be at 230 volts and not a dead short. Maybe that would make no difference
I'm sure that in high current situations, it can cause overheating. However, despite it not being able to overheat within 125A, any added heat to the system is not helpful when it comes to dissipating the normal system heat. Either way it's to be avoided.
A control would be useful to understand the temperature change when the cables go though a single hole.
If a section of metal was removed between the two holes to make a gap, would this be sufficient to stop the field forming and the heat build up.
I would be interested seeing you create a true shorted turn. I once did this accidentally when I installed a toroid transformer in a metal box. The box lid got squashed and there was quite a bang.
When I first learned of this rule, the situation was using a twisted multi cable (like a drop cable to your house) run on both the live and neutral. Where the two cables passed through a metal plate, there had to be 1 live wire and 1 neutral wire in each hole. Basically, untwisted and then paired together, as both cables wouldn't fit in a single hole. I'm wondering if it's the spacing between the holes that makes the difference. Like, instead of looping the cable (as in this test) through adjacent holes, but in one hole and out a hole further away or on the other side of the box. If this is the case, I can see choosing the simple instructions of using one of each per hole. It could be quite cumbersome to have to calculate a safe spacing. And we already get plenty of shady wiring.
I have only used 6 AWG wire once. Most of my experience is 12 or smaller. I know that I wouldn't be comfortable doing these tests, so ... Thank you!!
Great test John. I would like to see just the one line incase there is a cancellation effect due to the propagation of the magnetic field. But as others have said you do get the feeling that the regs are sometimes a bit regs for regs sake and not as close to real world examples as they could be.
The way you have it rigged John means that the current in the wires at the point they pass through the hole will be in direct opposition so the resultant combined magnetic field would be much reduced. What happens if you only have a single wire passing through one hole - more representative of installation where tails are inappropriately (widely) separated?
Nice experiment, but I will suggest an improvement if I may. Your temperature probe is going to pick up the wire itself heating up inevitably. Let's assume that the metal box acts as a choke on the wire and adds imaginary resistance to it. Here's what to do: Run your constant power supply through your wire in open air (no box) and measure the voltage drop on it as accurately as possible. Then install it in the box, reattaching the ends as faithfully as possible. Measure the voltage drop again. The difference in the voltage drops can be used to calculate the impedance of the choke and the heating power in the sheet metal.
2°C in 5 minutes could be very substantial if this rate is maintained 24/7, right?
Not necessarily because the metal box dissipates heat more quickly as its temperature increases (and so the temperature difference between it and the surroundings becomes larger).
In fact, it's likely that the 2 degree increase was caused by the resistance of the wires themselves -- or a good portion of it was anyway.
That's to make the erroneous assumption that temperature increase linearly over time. The answer to that is no they don't. An equilibrium will be reached when the heat being generates matches that being conducted away. If that was ever going to get to dangerous temperatures, it would have become obvious after 5 minutes as the temperature would have climbed a lot faster.
As it is, a quick calculation on the length of that 25mm^2 cabling within the box (I estimate about 30-40cm) would dissipate about 4-5 Watts. It would not surprise me if the great majority of the increase in temperature was from the slightly warmed air rising. I suspect if the temperature of the wire was checked it would have increased by a great deal more than 2C just from resistive warming.
Great test! I have always wondered what this would be in practice. Though I bet there are some variations on this test that would cause a greater heating effect. Proximity of cables, thermal mass of the case etc. I guess there is a point at which the case cannot dissipate the heat generated causing the conductors insulation to break down and then short. Excellent job 👍🏻
i was involved once with a television transmitter installation where they ran 3phase power to the main disconnect box using three separate conduits, one phase in each conduit . Those got red hot! Granted it was a hundred amps and the metal separating the conductors was not just the metal box, but was a length of about 10 feet of conduit; but that situation was an example of the same effect. The conduit / metal box created the core of a transformer.
The solution was to run three separate smaller size wires in each of the three conduits so that each conduit contained all three phases adding up to the required wire size for the current draw.l
A little late for a reply. The condition you describe is because the metal conduit was connected at both ends. In industry if you had large single core armoured cables carrying several hundred amps, the gland plate at one end was always insulated to stop Eddie currents circulating around the armouring or conduit
It's interesting as the electromagnetic affect consideration now appears on the schedule of tests for an electrical instalation. far more worrying that we now have to use metal consumer units on a TT earth system . It was once considered a no no to put mains tails with no back RCD protection into a metal enclosure but now it's fine with a plastic stuff in gland . load of tosh in my view. love your methodical uploads ,as interesting as Big clive .
As a sparky doing remedials ,I have had to reroute cabling though the same hole (3ph) which has been running perfectly ok for years, your findings seem to dispel any reason for doing this.Maybe it's just good practise?
It is actually a regulation (521.5.1), so is required to comply with BS7671.
Whether it makes any difference in reality is another matter.
Under the 16th edition regs it says "conductors shall not be surrounded individually by ferrous material or that provision shall be made to prevent eddy (induced) currents." So its not saying NO full stop, its suggesting there may be a problem by doing this so if an older existing installation which was installed under those older regulations is operating normally there would be no need to change the cable routing into the enclosure.
Hi jw on metal c.u dose it matter if the earth passes through a different hole to the live and neutral or is it okay as long as the live and neutral go through the same hole thanks
Good work, very interesting, i also have been taught to cancel the incoming cables, been years and years ago, the good old days
Good vid, not to ask a silly question but would the current induced in the metal be significant enough to generate a shock or be picked up through a tester?
One might wonder whether the 2C change was as much due to environmental change? In any event as any induced current would be in the steel case, one would expect that to be the subject of any increase in temperature, not the supply cable.
Are you using an arc welder off screen to produce this current? If so, does it have a rectifier in it? I wouldn't expect pulsed DC to give you the same Eddy current effect as true AC. Really interesting test, I'd be curious to see your whole test setup.
Details here: th-cam.com/video/35VpIE1oKsc/w-d-xo.html
No rectifier, just 50Hz AC.
@@jwflame thanks for the info! I guess it makes sense that a flat steel plate wouldn't get much by way of Eddy currents, it's how we design transformer laminations after all!
Interesting, I suspect you could get a better induction heating effect by putting a few turns through the two holes, although I suspect that even one or two turns would not produce enough effect to raise the temperature significantly.
Half a turn it seems is not nearly enough to have a measurable effect.
I can see why someone might be daft enough to do this, to "keep the excess wire neat", in the same way that people operate large coiled mains extension cables still coiled up on the reel (to keep them neat) and wonder why they start to cook after prolonged use.
Not sure why did you expect significant eddy currents resulting from a couple of wires going perpendicularly through a thin metal plate. You mentioned transformer core lamination design, well it is almost exactly the same scenario here with two notable exceptions: 1. it is like just a single platter of a transformer core rather than the whole bunch of them; 2. it is wire going through the plate once rather winding around it. All in all eddy currents at 50Hz should be expected to be insignificant in those circumstances and so they proved to be.
I am curious. Doesn't the impedance of an inductor occur within the copper itself? Would this not theoretically directly reduce the rated current carrying capabilities of the wire, however small that reduction might be? You should measure the effective henry rating of the fuse box acting as an inductor in a setup like this.
Interesting, if i had to bring the tails into 2 holes I'd cut a line through the bridge thus making it one hole.
I really think we've taken a step backwards with the regs here as there are lots of plastics that don't support combustion
glenwoofit As Wylex now unhelpfully put a single 32mm hole the centre of the bottom of their metal CUs with 20mm ones either side, I was going to do exactly that here (cut a slot between two of them) so the meter tails can enter neatly in line with the main switch. But I wasn't expecting the eddy current heating to be so small.
+Graham Langley That's exactly what I did - a single hacksaw blade cut - and the sparks was quite happy with it.
i have first hand experience of this and have found in every case where heating of the enclosure occurred both the neutral and earth were taken through different holes as each other and line or both earth and neutral in same hole but line in different one. in one case where all 3 phases neutral and earth had been taken through different holes. the supply to the hotel would cut off for 30 seconds then come back. this only stopped when i cut slots between each hole. cant begin to explain how or why but i was called after 2 years of this happening and the only fault i could find was supply taken through different holes and it stopped when i slotted the holes.
An infra red camera would be useful to check this type of heating. FLIR make a neat one that hooks up to an iPhone or iPad.
I am going to do what you shouldn't, and that is comment on the video before I've watched it all the way through. However, there's a reason. That's because, before you even do this test, I'm going to predict that there will be no significant heating caused by eddy currents induced by the magnetic fields, even if you put 100 amps AC through the thing. Transformers (and induction hobs) have got large numbers of windings designed to generate powerful magnetic fields. A couple of parallel wires a few centimetres apart will not generate enough field to induce large current flows.
So, not I will watch the rest of the video and see if my prediction comes true of not.
**** update ****
My suspicions were confirmed. I would also suspect that the slight warming that was seen at 125 amps was largely down to convection currents from that loop of wiring. Assuming that it's about 25cm long (or about 10 inches), then that length of 25mm^2 cable will have a resistance of 0.0005525 ohms (which doesn't sound like much). However, power resistive losses are resistance times current squared. 0.0005525 x 125 x 125 = 8.6 watts. I think that putting a 9 watt heater under that thin bit of steel could easily account for the great majority of the warming effect. Of course, at 25 amps there will only be about one-third of a watt, so that would be negligible.
nb. high powered cables running parallel to steel panels would induce more current, but at right-angles it's going to be negligible. I wonder how many of those stories about overheating panels are more down to resistive losses (including from poorly made terminations) than induction currents.
this test is floored you said your self about transformers just look at a simply diagram of one and you will see one side of the transformer is larger so putting one cable through a hole and out another wont give a true result you would need to run an earth cable with the neutral or in its own hole to lower the resistance and unbalance the circuit then test.
I wonder does the voltage in the wire have any effect on this result ?
Like, jolly-good show. Per chance you could do a video in which you operate multiple kettles, all plugged into one multi-socket mains-extension lead. Cheers!
Take a couple of loops around it through the holes, with an iron bar down the middle of the loops. it wont do much either but you may find your metallic tools.
My impression (as a physicist, not a working electrician) is that the expected heating is not from eddy currents (the thickness of the metal limits those severely) but from the magnetic field itself and the resulting hysteresis (iron) losses.
Whatever the source, it is generally not significant except at much higher currents than you tested with or with more substantial (thicker) ferrous metal plates.
I am having trouble thinking of a simple experiment to prove one way or the other. I suppose that using a ferrite or other composite material which was magnetically active but not electrically conductive might do the trick.
If a significant heating effect was observed then the test could be repeated with a non ferrous metal such as aluminium. If the heating is caused by eddy currents then it should still occur but if it's due to magnetic losses then it should no longer be present. I personally can't see why there should be any eddy currents at all because the lines of magnetic field will occur in the plane of the metal sheet so any eddy currents would have to be perpendicular to the sheet and there isn't any perpendicular path for them to flow in. The section of cable in this test that's laid flat on the metal case is much more likely to induce eddy currents but even then they will be small because the magnetic field in the air surrounding a cable is itself small due to the low permeability of air.
What about the frequency? If the power supply had a lot of noise, then I presume there would be more heating. Could be interesting to run the test at 500hz, 5000 hz etc.
Would there potentially (pun intended) be issues other than heating? Such as interference with tripping of ground fault protective breakers
John is this actually a fair test? 120A x 50v = 6000vA the aprox output from your welder. 100A at 230v = 23000vA the aprox output from a fully loaded consumer unit I could be wrong but suspect the heating effect would be higher.
I do agree I have seen metal consumer units with tails in separate holes with no noticeable heating present.
That's entirely irrelevant. All that matters with eddy currents is the induced magnetic field and the only thing that matters is the current. The amount of power being dissipated elsewhere doesn't matter in the slightest.
John in the intro to this test you said live in one hole and neutral in the other but your test it was the same wire in and out please can you explain
The two conductors would be L&N in a normal consumer unit.
The only difference between L&N is the voltage relative to Earth - L 230v, N 0v.
Magnetic effects are caused by current, the voltage relative to other parts isn't important. In this case it's the same conductor, but the key point is the current direction is different through each hole.
Does the main earth need to go thru the same entry point on metal enclosures?
Yes. 521.5.1 in BS7671.
@jwflame I am aware of this reg but I can't understand why , my thinking was if the L and N are thru different holes the eddy currents can cause a build up of heat over time but if there's no current going thru the earth except in a fault it would only be for a few seconds so wouldn't have time to build up heat.
The more I see of standards outside of the US for electrical the more I think the US is not so backwards. In the US the mains comes in via conduit, it wouldn't be possible for someone to even think of running one wire in one hole and another wire in the other.
This sparky is a solid guy
Great putting this out there, but the measuring of temperature was not where I saw this test going, the rise could have been down to the transference from the Conductors, or the surrounding air temperature rising over time?
Why not do the same test but this time put a Voltmeter attached to the M/C Consumer Unit and the other to an Earth Spike [run a remote Earth Cable] in the Ground, somewhere likely to get a Good return path, now measure the voltage at the start and at each stage of the Test.
Mr Spence Eng
Good evening John, May I ask and maybe state, did you post this video as BS7671 Amendment 3 states that in 2016 all CCU which are to be installed have to be metal.
Matthew Pye Not specifically, although it is certainly relevant to that.
Matthew Pye They don't HAVE to be metal, they have to be of a non combustable material
Excellent video
Was this Ac or DC supply.
Another display showing the ambient temp, would have been a good idea.
It would be interesting to see what happens if you increased the size of the gap
Does a t&e cable create Eddie currents between another t&e cable when they are put in separate holes?
No, current in a T&E will be equal in both directions, so there is no magnetic field.
@@jwflame thanks for the reply.
Just wondering, 100 amps at 230 volts Vs 100 amps from a transformer or what ever you used there at maybe Extra low voltage, The mains kilowatts would be much much higher would it make a difference?
They invented the TRANSFORMER!
We were taught in trade school if you did this in a metal board ( pass a single conductor through an aperture )
Put a cut between the holes to negate eddy currents
Remember guys balance your loads!
I know mains is low frequency ... but now try this with high frequency. You might get more heating, because of the skin effect, which makes the thick metal box become a thin metal box, in respect to where the electrons flow... thus, it would heat up more because of the higher resistance .. or so that is the idea XD
2C might seem like a small increase, when outdoors (where the wind will be taking the heat away), but in your enclosed basement, with no wind...
+Nalianna Most or all of that 2C increase was due to resistive heating from the wires, not magnetic effects.
+John Ward i agree with that the heat rising from the cable is what caused the change, however it would have been nice to have seen another meter to read the heat from the cable, a closed box in a not open to the basic elements of nature. i know this wont change the results of what you found here but will be interesting to see how the tempreture will change used normally of just the wiring...
a test using a miligauss meter would be interesting to see is someone was to put cable in one hole and then in a hole either side of the unit as a pass through with like mains in then to a shower etc, then to test the induction of all four corners as if its like a transformer.
Question:
Was alternaing current used?
Was the Metal consumer unit connected to the earth/neutral of the power supply?
What voltage was being used?
a) yes
b) completely irrelevant
c) completely irrelevant
@@TheEulerID Could you please explain why you deem two of my questions irrelevant.
@@ribblehead02
Fine.
Eddy currents are induced in a conductor by changing magnetic fields. The magnetic field induced by a conductor depends on on the amount of current flowing through it.
Whether the case is earthed or not makes no difference, nor does the voltage applied across any load. Only the changing current matters.
nb. transformers work by having many windings to build up the magnetic field, and mains frequency transformers use iron cores to, for want of a better word, amplify the magnetic flux, and those do have significant heating from eddy currents.
Is the injected current ac or dc? Because I don’t think you will get eddie currents with dc.
AC, 50Hz.
John Ward thank you for the clarification 👍
? DC ? The IET is a recent creation formed from the combination of two institutions founded in the late 1800s (Wikipedia). In the practical guide book published by the IIE in the 1970s: a single hole or slotting between holes was recommended.
In years past DC distribution and control was widespread.
? Has anyone experience of high amperage DC in single core cables that pass through a steel plate, welding for example ?
what would it take to make some heat?
I also remember reading somewhere that the CPC needs to enter via the same entry as the live conductors, true?
Normally it would, although the CPC doesn't carry any current in normal use so it wouldn't make any difference.
What he using to power the tails and increase amps
th-cam.com/video/35VpIE1oKsc/w-d-xo.html
Never knew the reason why so thank you
Could the heating come from the (i^2)r losses in the cable carrying the current? (instead of from induced currents in the steel)
My thought too. I'd guess that loop of cable in the box is about 25cm. A bit of calculation on 25cm of 24mm^2 cable with 125 amps running through it shows it dissipates about 8 watts from resistive heating. I think that could easily explain the reason the box warmed up as convection currents would have risen.
At 25 amps, then there would have been only about 0.3 watts from that source.
this is something that we used paxoline for in all installations cut a slot and then cut the paxoline and pass the cables together through it, mind you were were talking between 300-600 and more amps loading this is basic 1 st year apprentice training FFS
I saw a dramatic overheating in cables that were feeding a low voltage but high power inductive load all the cable overheated like a living hell until we have then separeted
JW Firstly you videos are very informative. I feel that for the eddy currents just bringing a conductor through the steel enclosure with a load on is not the correct way to test this theory, In normal situations the line and neutral conductor would be entering the enclosure and then the loads placed on these cables would be from inside the enclosure. I was told a story when i was at college many years ago now how a TP+N supply was installed in singles conductors and installed into the DB singly. A 2kw load was placed on an outgoing circuit and the heat after a short while blistered the coating on the DB. Again possibly urban legend. But would it not be an idea to test this theory in a video. Also the 2 deg temp rise was most likely caused but the conductor temp when running a 117amp load. I look forward to your thoughts on this.
+Mark “Marcuscrackus” Everitt How is this setup any different to what you described? What do you think would happen differently to the field lines around the conductors?
Great video
Something I've thought about.
Thanks👍
Eddie and his currents.
Great test video, thankyou.
I really don''t get this experiment. It appears to me that the net magnetic field on the panel would be 0 since the current at any instant would be in separate directions because the wire is looped in and out of the panel. Magnetic fields would tend to cancel each other. If he had put 2 separate wires through the panel with each wire connected to the load resulting in additive magnetic effect he certainly would see a different outcome.
I don't think you understand the concept of eddie currents, the metal divider (between the 2 entry holes) is in a constantly changing magnetic field, this would see a current flow generated but like the video implies at domestic level this is rarely if ever an issue, the metal splitting the cables apart interupts any cancellation of the magnetic field would occur if the cables went through the same metal opening.
Would be interesting to see if a saw cut between knockouts actually works or if i've just been wasting my time.
one wire coming into the panel is neutral and the other wire is live?
it looks like both wires are live in this setup.
In a normal installation they would be line & neutral.
In this test power was obtained from an isolating transformer so L&N does not apply.
Hi John, Did you use ac in you test?
Yes, 50Hz.
@@jwflame If you tried this again with DC it would confirm conclusively whether the heating effect was due to ohmic effects in the cable or eddy currents in the case. Plus an added bonus of a spark of some significance when you disconnect the supply !
Hi John what are you using as your power source?
This: th-cam.com/video/35VpIE1oKsc/w-d-xo.html
No, more like a monster 120A oil cooled welder. lol.
If I hadn’t seen your face I would swear Clive Anderson was narrating.
Was that DC or AC?
AC, 50 Hz
Wouldn't that metal box need to be bonded in order for an induced current to flow through it? Connect the box to earth.
That was quite interesting, apart from putting the wires through separate holes. Whats the go with those tail clamps, as they quite clearly separate the tails inside the enclosure. Or have they already looked into that..?
An enjoyable and well exicuted video, but i cannot stress highly enough the very real problems that eddy currents cause in poorly designed switchboard and cable ladder installations. Eddy current heating typically is only an issue in installations running over 250Amps @ 50 Hz, so whilst your video addresses the (watch makers currents found in domestic consumer units), try the same test with the same consumer unit fitted inside an insulated wall cavity with third order harmonics and a few well loaded RCBO's all adding to the heat rise. I earn a good living fixing these and other problems in 500+ Kva installations, unfortunatly I am usually too busy trying to get the installation back on supply to take videos of the discoloured paint, damaged cable insulation and hellish buzzing noises caused when people go off making iron circuits around unballanced currents after seeing these sorts of dangerous videos.
"....these sorts of dangerous videos."
Sorry but how on earth is this video dangerous? What you've described is not what he's showing here is it! What we're looking at is a simple metal consumer unit, in the cold outside air, with circa 30Kva I think?
I genuinely found your comment interesting to read, I don't work in your industry but I'm considering a career change and it's interesting to understand what type of work an industrial electrician may do day to day. But this is not a dangerous video because he's not misrepresenting anything. Nowhere does he imply we can all ignore the regulations now and do our own thing. Quite the opposite.
Lets be practical, this isn't aimed at Domestic Households of a 100A or less.
I'd imagine if you took an enclosure in a tube or train station, with 25kVf, and the train pulling 2500 kW, I'd imagine a small bit of metal that should of been removed, would get toasted by Eddy Currents.
Maybe try this experiment with tin foil :) ?
Great series of videos John
So 120A 220v AC and your connecting the most dodgy pair of crock clips without isolating the supply or wearing rubber gloves. Cool. i wanna go.
I'm not a great fan of steel consumer units, didn't the London Fire Brigade ban them in the eighties (16 Ed) and now as if by magic they are safe from being a fantastic short circuit to the mains. ummm.
Are they the same muppet's who insisted all fire extinguishers should be red so you visually spot the different type in low visibility and hung 1m off the floor so that when you are crawling around on the floor in a smoke filled room to get your last breath you end up knocking a great hunk of steel off the wall onto your head. Thought so.
Look carefully it a welder so the voltage will be 50 to 60 volts welders do this every time they arc up
Myth Busted, in order to prove the effect accurately it would have to be good old 220v supply, i tend not to connect my welder up through the consumer unit - as shown. i guess DCEN means DC so yet another flaw in the experiment. Shame i thought John had stumbled across a method of telling the London fire brigade why we got rid of these things in the first place in favour of slow burning, zero halogen, self extinguishing plastic. In 20 years the rules will go back the other way, so they can charge more money and write another edition of the regs to get us all back on courses.