Voltage Drop in Electrical Circuits
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- Опубликовано: 8 фев 2016
- A demonstration and explanation of voltage drop in electrical installations.
The excessive volt drop shown in this video was caused by a fault with the supply, which was fixed shortly after this video was made.
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Really starting to like this guy with his straight forwardness and bluntness.
Got to be the best online tutor in this field, every video is clear and made to be understood by even for the most novice amongst us. Cheers JW 👍🏻
Your explanations are so simple to understand. Thank you, John!
Great video as usual John. I had an issue similar to that house you demonstrated on, apart from voltage here dropped to ~100v. It took WPD so long to do anything about the fault in the street that the cable under the footpath actually blew up one evening, taking out one of the phases and therefore a third of the street for over a day whilst they temporarily re-connected people to a different phase whilst they made the repair (which typically involved them destroying my front lawn, again).
Your delivery and content are sublime. Thank you for uploading.
Hi john I have my 17th edition exam on 15th of feb and I must say your videos have helped massively in understanding certain things that I was unsure of to start with. thanks pal :)
That opening line *"...Hello I'm JW..."* is becoming legendary. 😁
That reminds me of a similar issue we had up until about 15 years ago, but in our case it as a 6 volt drop for a 2kW load (e.g. Kettle) as our mains supply ran for something like 500 metres to the transformer. It wasn't a major issue until my my brother (who lived with us back then) got a 35A welder! When I reported the voltage dropping issue to ESB Networks, in just 2 weeks they extended their high voltage lines right up to near our house, fitted a new transformer and now the voltage drops by about 2V in the socket next to the kettle when switched on.
the distance of 500 meters to the transformer was probably the main issue
Similar issue here. We are 300 meters from the transformer plus 70 meters of 16mm 3 phase cable.
When the electric mower starts it's a significant dimming of the lights, and the phase previous in the rotation will actually brighten slightly.
Oddly, resistive loads will push the phase next in sequence up by half the drop on the loaded phase.
JW should have been a school teacher, I might have gone to school then, love the vids JW
So true.
+DC when I was at school all you did was copy what was on the board, in silence...
*****
same here. I was born late 60s. My first school was a typical victorian school. All on benches with slate board. My next school had round tables and it was chaos. My junior school is where i gave up learning from school. My education is very high but have no qualifications. No way was I going to spend years getting in debt to do a degree so I can flip burgers
youre a good teacher, I wish you teach millions of students.
I do hope once the kettle boiled the home owner made you tea!
Again, great video JW.
Great video and explanation John, I really enjoy your videos as you explain them in good detail that are easy to understand for both students and experienced Electricians like myself. Keep up the good work. 👍
Great as usual; thanks for your efforts John. Could you do a video on voltage drop in ring circuits?
Very useful, clear and concise information as are all your video's. Thank you. Aside, your presentation reminds me of the 1970's Open University programmes that used to air on BBC2 in the wee small hours (showing my great age now!). That's meant as a compliment by the way :-)
Thank you John, I am more accomplished in mechanical engineering than anything else, however I am fully aware of how useful knowledge electronics is. I am slowly getting my head around it.
You are clearly very experienced in your subject but unlike many others, you can communicate the subject in a very chapter one way. Many thanks again.
Nicee well doneee
JW. Always very informative and clearly understood. Really enjoy the videos
Thank you very much for sharing your vast knowledge base and expertise J.W.
You do brilliant work thank you I always use your videos too brush up on things I'm not 100% sure
Thanks for the great content
very interesting John, similarities can be seen when considering volt drop in a battery and external load, the battery will also have internal R, very similar to the R in the mains system you explained,
enjoyable!
JW nails it again, another excellent video.
Awesome video. Cleared up a lot of concepts for me. 👍
Very thorough and simply explained
Thank you Mr. Ward. Helped a lot.
Thumbs up from me, very well explained and clear, thanks JW.
Robin electronics , they were located in Watford and made the Robin range of test instruments in the late 90s they stopped trading and re located to Chesham and rebranded as kewtech industry’s and continued to make the Robin meters but changed the colour from yellow to grey and rearranged the model numbers , ie Robin KTS 1620 became kewtech kt 62. Since then the Robin brand has been used by a number of different manufacturers including fluck and amprobe . Great video John very well explained
Thanks, john ward , its would take a long time for me to understand if not for your video, appreciate for your great effort.
Why the hell has someone thumbed this down? Some people just hate education.
AintBigAintClever . some idiots are just born trollers. I wish, every time someone trolls, a magical hand will slap them around the back of the head. HA!
just your average idiot on RUclips
There's a lot of know it alls on youtube who think if you didn't do it the way I would have done it then you did it wrong. That's my guess on who down voted the video.
AintBigAintClever what’s that saying about educating pork?
I would bet half of them are people who missed the share button and accidentally thumbs downed the video.
Hi JW really enjoy your videos and this great explanation of voltage drop. One thing I did note was that there is no mention of the utilisation voltage. I believe in the UK as with Australia the service provider is permitted a +10%, -6% variation in supply at the consumer point of attachment. Further to this BS 7671 and AS 3000 permit a maximum VD of 5% within the premise. Therefore the maximum & minimum voltage (or utilisation voltage) experienced at the consumers outlet could be 230VAC +10%, -11% or 253VAC to 205VAC. A voltage as low as 205VAC is permissible.
Fantastic, concise explanation. Where were teachers like this when I was at school?
Another great video by JW👍
excellent video John... bravo !!
Thanks John, I partly realised my problem but I was still unsure, It was doing my head in as to why I was getting 0.00 on so many results
Simple and very explanatory, very good
Very well explained and understanable Well Done.hank you.
Nice video thanks, so if V = I.R then the lower the resistance of the wire, i.e. the thicker the wire, the higher the voltage drop along the wire & thus the more voltage is available to the loads?
Very interesting.I look forward to your videos.
Thanks John. Well explained.
I've noticed voltage drop on my simple Kill-A-Watt depending on what's connected, along with a corresponding dim in the lights when high power devices such as the kettle, and to an even larger extent, the shower are on. I've also noticed voltage rise at night, presumably because less people are using electricity. I wonder if the frequency increases at night slightly as well due to less load on the generators, although the power stations will be throttled back as well to counter this.
I'm glad to read this was due to a fault as a near 10v drop at 10A is ridiculously high. That 1 ohm resistance is the equivalent of 135m of 2.5mm^2 copper cable (so almost 70m of length on a radial). It would require a massive ring circuit to get that sort of drop.
In my place mid afternoon. 250v on the 32A ring with nothing on. Measured voltage in a double socket in kitchen - 250v. 800w Toaster plugged into same double socket - turned on drops to 249v. Two rings on induction hob on (separate 40A circuit), drops to 248v. Put 3kW oven on, drops to 247v. Quite pleased.
Maybe very different at peak times.
JW you the best man keep it up!!!!!
Thanks John for the video. I would like to ask about my problem. I am not licensed to do power repairs so I improvised.
A house that has a 10+ year old fridge and has just started beeping a single beep from the kitchen when you switch the light on in the garage and other switches around the house but is not consistent.
I have plugged the fridge with an extension cord to other power points and have a power point with a safety switch included which has never tripped but it still has the single beep.
The beep is the same beep when you turn on the power at the wall or leave the door open too long.
Do I need a new fridge or call an electrician but I am also curious first and like to make an informed decision.
The 2KW electric radiator in this room is currently giving a good example of how wires have resistance. The wires are cold, but certainly more pliable than they were before switching the radiator on, and the plug has a slight warmness to it.
Another great presentation.
The mains voltage in my area generally sits around 240 rising to around 250 at night when the load on the transformer is less. I have moved a number of times over the last few years and seen similar results in other areas but i have never seen the voltage dip as low as 220.
I did wonder why the voltage was so low, as whenever I have measured mine, it has been above 245V: the supply industry likes keeping higher voltages than the EU standard of 230V, as we end up using more power! You gave the reason at the end. I have always preferred to err on the side of larger conductor sizes: in my electrical days, I always used 1.5 sq mm for lighting.
"the supply industry likes keeping higher voltages than the EU standard of 230V, as we end up using more power!"
In general you don't. Take that kettle. Feed it with a higher voltage, and it will boil the water faster and it will turn off quicker which will counteract the increased power usage. The same with a washing machine, or a dish washer, or an oven or anything else which contains a thermostat. Things get up to temperature faster and they then turn off quicker. In the case of devices which contain modern power supplies and draw a fixed amount of power, like a TV, a computer or something similar then the device will draw less current at a higher voltage and there will be less power wasted in the wiring.
Higher voltage supplies are more efficient. The current passed is lower for the same power which means there's less wasted power in the wiring. That doesn't just mean the domestic wiring, but it feeds back through all the levels of the transmission network. Run, say, 5% higher voltage at each level and that means about 5% less current which means about 5% less power loss in the cabling. Drop the voltage so that it's actually 230v that is delivered rather than 240v, then then more current would have to be delivered for the same power.
As for the EU standard being 230v, it's not. The requirement is a range which means that anything from about 215-250v complies.
What was your fault loop impedance? My guess is a loose connection at the SwitchBoard or Fault at the supply transformer
Very interesting video and real life situation.
Great explanation
Thank you, so helpful!
The Copper resistance is constant!
or changes as per size or length changes!??
Great video! Very helpful. I am trying to sort out a very simular situation in my newly built cabin. I’m 300m from the transformer that I share with my neighbor who has 3 cabins on the same meter. (I believe the transformer is fairly new but small at 5kw.) I put in 16mm2 aluminum (5awg) underground wire to my cabin (my meter is by the transformer, 300 meter from the cabin.) Without load my supply is between 215-235v depending on the time of day 221v most of the day. However my volts drop the same as yours in the video. 10 volts for the 8a kettle, 12 volts for the 10a oven (on its own, different circuit). It can go as low as 180 if I accidentally turn on the oven, kettle , and 8amp well pump etc. my question before calling the electric company is the following. Would testing the volts at the meter with and without load tell me if the drop was on my end or on the electric companies end? I suspect the major issue is the electric company but would like to be clear before they come out and say nope everything is fine.... Thanks!
Yes, it would tell you that because the voltage being “robbed” happens more and more as the current goes down the line. Thus, at the beginning you have all the voltage and at the end of the line less.
Good series Sir thanks v much
thanks Mr John
what would be interesting jw would be a video showing the sequence of tests at the c/u and why certain tests are carried out and stuff
RK 180 check out Chris kitcher. Routledge. QR codes 1-17. All the tests in sequence.
Hi John great video once again. Am i correct in thinking that as the kettle element heats up the resistance will be increasing slightly and also further decreasing the voltage until the water boils and the thermostat trips the kettle off?
Resistance does increase as the temperature increases, but for the temperature increase in a kettle element, any change in resistance is insignificant.
John keep up the good work, Maybe you should think about lecturing at your Local college?
so how about voltage drop in DC? if we have 5V supply and a 3V LED, the resistor ohms should be calculated with the V of 2, so how was the voltage remained higher than 200V when the kettle was turned on? if we use several devices voltage drops and to make it right amps goes up to fill up the watts right?
John - Would you like to comment on a street, where say most owners had electrical cars, which were charged from midnight to 6 AM. Would the voltage drop be significant? Would the mains supply be overloaded? Would the street need rewiring?
Very well presented. In our general math we are told that Parallel loads the voltage is the same at each load. The resistances are added together RESULTING in LOWER resistance and INCREASED amperage.
In your example the resistances are in series. Thank you. Comment please.
The resistance in this instance is that of the supply cables and circuits within the property. That remains constant, but as the load (amps) increases, the voltage across that resistance also increases, V= IxR.
Parallel loads only have the same voltage if the cables connecting them have zero resistance, in textbooks this is assumed to be zero but in reality cables have some resistance although it's usually very small.
The installation in this video had a fault with the supply (high resistance connection) so the effect of voltage drop was much larger than normal.
Amazing video ur so clear and u speak slow other country people can understand u fantsstic
I'm now regretting not measuring the voltage drop on the old CU here before it was changed late last year. I'm definitely no longer seeing the lights dim slightly when a particular vacuum cleaner is used, but that may be because most of them are now LED and nowhere near as voltage-sensitive as incandescent lamps are.
What setting do you put the machine on?
Great video, as are all those that you have produced. As an aside, is that a Hammond T- series organ in the background?
I have one that I am currently rebuilding, - great sound.
Keep up the good work.
+David Stone It's an M series from the 1960s, all valve/tube amplifiers.
Interesting. I thought only the current flow in ampere would change in a parallel circuit. So there's a voltage drop as well, cause the cable resistances are in a serial circuit. I didn't expect such an impact on the voltage with indoor house wiring in comparision to outdoor transmission lines.
Thanks john
Just out of curiosity I tried it on my British system. Ebay multimeter not a kinky Fluke, starting at a fairly statiic 248 volts Voltage drops by 1 volt for each pair of slots on a 4 slot toaster. Total load about 1500 watts. Guess my wiring is a little more substantial than the apparent damp string used in that house.........
Your mains voltage already seems so low to start with! I've just measured my mains voltage and it's 248 volts, and turning the kettle on only drops a few volts then it climbs back up while the kettle is on.
Oh, you are so lucky with 10V drop at 3kW ;) In my place when I switch my 3 kW kettle voltage drops from ~220 to around ~190... And kettle draws around 2 kW instead of 3
On the other hand in an apartment with new electrical installation and direct short run of 5 mm^2 connection from fuse box to outlet for stovetop (2.5 mm x2 parallel on both L and N in preparation for 3 phase supply) I get just 3V drop at 3.7 kW of power ;)
+mibars Where are you located? That kind of voltage drop sounds like what I'd expect in rural Italy but in your case it seems to be caused by your house wiring. In Italy it's the grid operator, they'll seriously string over 1000 m of 6 mm2 wire on poles supplying several houses!
Ragnar8504 Poland, countryside, very end of power line. Power line that was supplying two houses at this end back when it was constructed now supplies I think 7 or 8. I can clearly see when my neighbor starts the welder.
mibars i
It’s common for uk to have series instead of parallel?
Great video👍
Excellent, informative video, thank you! I am currently trying to figure out if something is wrong with the power supply to my house. The most voltage I see is at my sockets is 226V and when I turn on high load appliances the drop takes this down to 210V causing some of my equipment to cut out and lights to flicker etc. Should I contact my power supplier? My father gets a steady 240V at his house but it is in a different village.
210V is too low, and the drop from 226 to 210 is excessive, so you should contact the supplier so that they can investigate.
The example in the video was due to an underground cable fault which has now been repaired - when loaded the voltage only drops by 1 or 2 volts now.
Angus Smith - Had similar situation many years ago. Power supplier should take care of that...But most times they don't/can't because of all the surrounding infrastructure (high cost).
In my case after complain they changed my house supply from one connector (barramento-put the correct English expression) of 6 houses to another, just beside that only supplied 3 houses.
Meaning it was far from perfect but got slightly better. Anyway I was the only one complaining (officially) all the others had the same losses but where not aware of the situation.
PS: During Christmas season (light decoration in nearby city) it went as low as 195V. Too many transformers, ballasts and a few other electronics lost...I payed the bill for all. :-(
John, thank you for an excellent, clear cut explanation. I wonder if you could extend this to add a comment about the effect of VOLTAG DROP on household electronic controls such as inside electric showers and low voltage lamps? We have lived here for 12 years without a problem but in the last week one of our showers has ‘stuttered’ running cool for about a minute until returning to normal. Meanwhile the overhead bathroom spots dim then flicker to life. From your video, I strongly suspect an incoming supply fault and intend to report this to our supplier,. Again, many thanks for your video.
Does the lighting in the rest of the house *also* dim? Because if it’s in your supply, it should affect everything.
Or have you gut it fixed by now and if so what was it?
Your the best thank you
Here is the US a kettle is about 1200 watts at best. I am always amazed how quickly a kettle boils when I visit the UK.
Mr John where do you live?If in uk...where?I wish to meet you.
How did you discover the house with the voltage drop? Ie did your customer report problems, if so what were they experience that resulted in a call out? (Was it flickering lights or something worse)
Also I love your videos. It’s cleared up so much in my head about how stuff works!
Kitchen light wasn't working - an older type fluorescent tube with magnetic ballast. Would work perfectly some of the time, and at other times it wouldn't stay on due to the low voltage.
Good stuff thank you
John, very well done! Can you please do a voltage drop video for motor loads? Make sure motor is loaded, not free wheeling. I would greatly appreciate your opinion!
Here across the pond, NEC suggests 2% for feeders and 3% for circuits, with 5% max of both. Suggestion, not code. Your transformer in the diagram is a 3 phase 4 wire wye, correct?
Regarding the utility company having an issue, my instinct and experience suggests that their transformer has lost its ground connection at the center point of the transformers. So, your voltage issue is what I call a floating reference point. It needs to be grounded. If you find what the fix was, let me know.
Sorry, I just saw that this is four years old! I was listening to every word and didn't check the date. Respectfully, Kevin
Our mains voltage is normally around the 248v mark.
John this is, like most of your videos very good,
mike bkk
So, if I connect everything in parallel, I wouldn't have a voltage drop. Or if I reduce c.s.a of conductor I will have constant voltage v=IR
Dude, this is why I insist on only 24 ct gold electrical cabling... Also why I am deeply in debt.
Gold is worse than copper, silver is better....
just use cryogenic coolling to go to 0kelvin something and use a supraconducter.
I use silver cabling, the resistance decreases with age ;-)
@max marrero Hello hello, hello! You seem to know a lot about it.
Evening all😅
Did you explain why the voltage dropped when you turned on the kettle? I just got from this that the cables have a resistance by themselves and this is why the theoretical value is not seen in reality. Maybe I missed something.
great video
Thanks John, another great video, only discovered recently. However, I’m still unclear about the voltage limits at the building intake, which according to ESQCR 27 which at -6% have a lower limit of 216.2 volts, BUT, it does not state if this is on no local load, or at your full permitted load, or anything in between, are you able to advise?
Limits are when on load - the voltage should not go outside of the limits at any time.
@@jwflame Thanks John, and another question if I may, if site load includes large heat pumps, currently without soft start, will the DNO accept very brief starting current "blips" slightly in excess of the agreed intake limit (fused at 100 amp for the site I'm helping advise friends on)?
@@9jws They might accept them. Such things should be notified to the DNO before they are installed.
Thanks again John, and yes they were apparently involved from the outset, but my enquiries continue. This all started from me helping advise friends who live at the end of a long private lane, and effectively the last house on the network branch. All houses very large, with corresponding large potential loads (in their case, includes 4 large heat pumps, 2 for house and 2 for pool, so an interesting installation). Measuring the Ze today, on no load, I got 0.55 ohms, but still trying to establish if TNS or TN-C-S as although it presents itself as TNS, I'm aware of an underground change in cable type (my son noticed it while doing some trench digging for them). Anyway, it got me thinking about the measurement of Ze generally, and even with no load on this house installation, others on the network were still connected, so formaing parallel loads, the demand on which will affect the measured Ze when just using standard loop testers or multitesters on a live network. I tried simulating this by also measuring Ze at the supply, with various loads on in the house, and sure enough, very significant changes in the measured value of Ze. Any thoughts appreciated.
Incidently, with a load of 64 amps, the supply voltage was just 206 volts. pfc is a concern too as as heat pumps also use type C breakers (currently without RCD's), and of course the supply 100 amp fuse, a standard BS 1361, so no hope of tripping MCB's or blowing the 100 amp fuse in a resonable time if a short circuit fault situation. A challenge for me too is explaining the adverse fault performance of the heat pumps under low voltage conditions, and the implications on the cold weather COP, but that's another story and needs my drives engineers and refrigeration engineer hats on once I've sorted this lot! Beeen retired over 10 years now, so having to research to get back up to speed, but it's keeping the brain ticking over!
@@9jws My ex-next door neighbour installed an industrial MIG welder in his garage. I had to live for years with my lounge lights flickering and strobing into the late evening thanks to numbnuts next door with his cut price tractor repairs. Luckily he's gone.
I love the way John says, "some moron"
hi JW love your videos, this video is absolutley good kirchoffs law proved your answers but how did you get 0.5 ohms for the conductors? or is this a fixed resistance for copper wire
The voltage drop (about 10v when kettle only was on) calculates to an ohm total in the conductors. Hence the assumption that it was about 0.5 ohm in each.
with the highest respect to Your videos, the cattle ,the toaster,the cooker are in parallel ....
in the first part of the video(turning on and off the cattle ,toaster etc.) Sir John discusses voltage drop on the appliances in parallel.in the second part he discusses the voltage drop on the cables(conductors),obviosly in series with the load----if the cables are too long they can "consume" the voltage needed the load to operate properly.The electricity is precise science--i thought Sir John could find a way (method) to differentiate the two voltage drops.
Thank you.
John if it says total cabinet load of 10amps dies the fuse in the plug have to be 10amps or it doesnt matter if its 13amp has the mains lead is 16 amp c19
If it states 10A, then use a 10A fuse .
+krisbham,in general kettle cords are less than a metre in length & the resistance in it would be so minimal,it's really not worth factoring it in,in the overall scheme of things.
Voltage drop will increase electricity bill?
John, do the electric meters measure only current or actual power used (because of power factor etc)?
They measure actual power not apparent power, the only time you would be charged for apparent power is in a industrial environment that is why you do not need power factor correction. Eevblog recently did a video on this subject you should check it out.
+Jeremy Hall Yes, actual power from measuring both current and voltage. Doesn't therefore matter what the voltage is, unlike those clip on energy meters which only measure current and assume the voltage is constant.
I was just wondering, are those individual mains conductors, going into the Fluke, double insulated?
Yes they are - both the 4mm plug and the wire is marked with the double insulation symbol. Rated Cat III, 1000 volts, and 20 amps.
Thank you
Sorry, just catching the first minute of this, need to start work.. But I was thrown by the change of location.. It makes you look different some how.. Will watch during lunch break.
So are all of the resistances all just additive and not multiplicative? I mean all of the components become parts of the load essentially.
Hi John I'm new to testing but since you own a fluke I thought you might be best person to ask, I'm getting zero ohms when testing about 6metres of cable feeding a shower surely I should be getting some value, I seen here on RUclips that there is a null lock on the flukes!! Have you any knowledge on this, thanks
On the older Fluke MFTs, the zero function is the oval button top left. It's the F2 button on newer ones.
if active, there will be a ∅ symbol shown in the display.
To reset, connect the test leads together, press and hold the button until it beeps (a few seconds usually).
very interesting multi-meter you have there!
Its way more than a multimeter its an installation tester tho the test he did in the opening scene you can perform the same test with a basic multimeter like a fluke 117