Calculating Cable Energy Wastage, Energy Efficiency
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- Опубликовано: 4 июн 2024
- Calculating the energy wasted in a cable for a given load current and conductor size & length.
The example in the video would be a high use electric vehicle charger, with the vehicle being driven approximately 150 miles per day, 5 days a week, 50 weeks per year.
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Did this for my PV installation. Insisted my installer used a heavier gauge cable to run from the attic mounted inverter down to the garage mounted generation meter.
My system generates nearly 4500W peak and has saved me the additional cable cost several times over since the system was installed 8 or 9 years ago.
My MCS approved installer had never before considered using a larger cable to improve the overall system yield - and my FiT payments will last for 25 years!
I used to write the electrical installation specification for the company I worked for. They were running continuously many large motors at the end of 3-phase circuits several hundred meters long, often through underground ducts and often bunched together. I required higher grouping factors than the regulations (to account for future additional circuits using the cable ducts) plus I required the final cable sizing to be increased to the next size up as determined by the calculations in most cases. Prior to this we could feel cables noticeably warm - not ideal in an area where flammable vapours were likely to exist. So this gave not just long term savings but potentially enhanced safety. On the same basis I would require high efficiency motors to be used rather than standard ones.
The saving going from 4mm to 6mm is greater than the figures suggest as what's not factored in is the increase in resistance with temperature. I'd also add that some devices don't last as long as they might when there's a voltage sag from the higher current draw at startup. Not so much of an issue with the trend to soft startup of things such as air-conditioners.
In general though my policy has been if 4mm is just fat enough spend the extra for 6mm if for nothing else than one day you might need the extra capacity and then you've got to pay again for the labor of installing the cable again.
TBH going to at least 6 for a car charger seems to be a cheap win regardless, even if 4 is compliant. Possibly even going straight to 10, after all the cable has value even if you give up the car after a couple of years.
Good to see this being discussed. Where cable losses can really add up is in larger industrial or commercial settings. Would be good to see some calcs by JW on say the savings to be had by increasing the conductor size for the supply of 250 amp 3 phase submains for example. Some of the ones I’ve seen recently have cables wasting several kW!
Forensic analysis of the topic as usual, thank you.
The calculation is an overstatement. It says 1250 hours * 7.4kW. This 9,000kWh. Which equates to 27,000 miles at 3m/kWh. Suggest the saving for an average at home charge is approx 1/4 of the stated amount.
On my current tariff as of April 2022 (Octopus Go @ 5p/kWh) the saving is a £1.75 a year based on 12,000 miles @ 3m/kWh.
Brilliant video!
Just making these same realisations today watching this video. Totally agree with you! @18.1kWh/100km (3.4m/kWh) & similar mileage to you (18k/kms) . Would take decades for us to pay for 10 or 16mm conductor gauges. 5p/kWh 🤯 Hope you still have those rates! Paying €0.31 here at the moment which is basically the market lowest tariff (Ireland) 😂
JW should stand in for Rachael Riley. Lol.
need to do this on my cooker and my fridge. Am in another country using 120V rather than 240V but all are the same basically. Wire cost here is way more but Electricity is more costly as well.
Beauty of 120v mains is that it wastes more energy and wastes more copper.
North America doesn't use 120V mains; it uses 240V split-phase giving 120V outlets for lower powered devices. High powered devices, such as ovens, in North America are wired using both "hots" and that most certainly includes dedicated car chargers. The calculations are essentially identical.
But look at the gauge of copper in home wiring in Europe vs that of North America and you see a significant difference.
Another great really clear video lesson. Thank you John.
Interesting calculations and nicely explained.
An excellent instructive video easily explained from a good orator.
Wonderful whiteboard example JW.
Clearly nothing wrong with my cables. Because as soon as JW posts a video, I see it and click on it. Just like you should / did.
John as usual the best explanation
Hi john. Nice to see you touch on this subject , this is something I have been trying to put across on some of the ev groups that I am on . One of the things that I have asked registerd installers of ev charging points is that when they do there calculations for volt drop do they include the length of the connecting lead between the wall Controler and the actual car . These leads are normaly 6mm copper and can add from 5 to 10 mt extra cable run . As the actual load is in the car not the wall charger ... to date no body has responded to this qustion . Also this type of charger is a constant power charger normally limited at 32 amp
So any reduction of volt drop will pay extra as the current being drawn will reduce as the voltage drop is reduced . I have done the same calculations on some that I have seen done with 6mm cable including a 7 mt lead and when you show the loss as a percentage of the charge taken it makes interesting comparison . Really good vid
Thank you for this. Much appreciated.Now i have a go to for when clients query things. I do actually see this coming as a reg
Ashley, if you're installing for clients, would you not already know this sort of thing backwards and forwards? It might have been interesting to see the losses as a percentage of the power delivered. And to see that total charging cost in GBP per year.
Thanks John--another informative video.
Another great informative video John thanks 👍
Great analysis John and very helpful 😜
Interesting statistics, although 37,500 miles a year (260 days at 150 miles) is five times the UK average 7,600 miles per car (stats for 2018). So, for an average mileage the difference between 4mm^2 and 10mm^2 the saving would be a bit over £2 a year.
That said, it's not a bad idea to have a bit of reserve capacity.
Isn't the savings from 4mm to 6mm and from 4mm to 10mm? Then we are talking under 3 years for the upgrade.
Yes, that's a better way of looking at it.
I remember doing this calculation in a place where I worked, out of curiousity (I had no electrical qualifications then). I can't remember the size of the cable but the loss over the length of the building was well over 1200W x 16 hours per day.
But that's wasn't the end of it. Becuase it was often far too hot there they installed air conditioning, so then they were using more power to get the heat out of the building.
la section de 4mm² consomme autant que mon air-conditionné tout l'été! =o
Merci
Great video john 👌🏼👌🏼👌🏼
Great channel, interesting.
From a Sparky in New Zealand.
Excellent video very interesting
Excellent vid that. Never even gone down the road of that sort of calc. Plus I have never been involved with EV units before. So if you say that a EV is charged for about 8hrs at 7kw (if I heard correctly), that's an awesome amount of power. How much would that cost you through a year to actually charge your car. That sounds like it's getting pricey. Technically by 2040 all new cars will be electric so I wonder soon if all new houses will have an EV charge point fitted as standard like they have a cooker point or extract fan.
You should have been a college lecture JW, you got a way of making stuff interesting, keep it up 😊
An 8 hour charge at 7kW would be 56kWh, and for a fairly typical EV that would be around 200 miles of driving distance. Using full price electricity at 15p per unit it would cost £8.40, or about 4p per mile.
However a petrol vehicle which did about 10 miles per litre of fuel (about 45mpg), would need 20 litres of petrol, which at £1.10 per litre would cost £22 - far more than the electricity cost.
Charging EVs will make the electricity cost seem much higher than typical household costs without EV, but it's still vastly cheaper than any petrol/diesel vehicle, and in reality the EV would be charged using lower rate electricity, particularly when done overnight, or if the property had solar panels and the vehicle was charged in the day.
Note also that someone doing that full charge every day would be a very high mileage driver, far more than most people drive. 200 miles/day = 1000 miles/week, or approaching 50k miles per year.
@@jwflame Always enjoy your videos and very interesting discussion. I wonder how well the UK is set to support the extra power requirements from an avalanche in demand for EV charging. Even knowing what infrastructure is required where, I suspect will be challenging. It is at this point you hope some clever people somewhere have been quietly sitting in the background working all this out. I think it is an interesting calculation - if you still have your calculator at hand as to what happens at 6pm when everyone gets home on a November evening and tries to recharge their cars, turn on their ovens and boil their kettles.
As always another excellent video , i hope if there any easy formla or equation to calculate the cable size debending on length and current and position of cable
اي اسلاك تشتريهم.. المفروض المصنع مجهز الحساب كامل.. كل سلك عن سلك يفرق و السبب هو كميه النحاس والمواد الأخرى الخ.
Yet another great video JW. May I ask how much do the cable specification book cost as I know they tend to be useful but quite expensive?
I love the way you deliver the subjects of your videos. Thanks again.
BS7671 is usually about £80, however if you just want cable ratings they can be obtained from cable manufacturers, most have them on their website for free.
Just to add, you can also use the tabulated voltage drop values in 7671 to calculate resistance and energy wastage of cables
Thank you 👍🙏
@Jhon ward great video. Please make some practical video on proper size cable for solar installation.
Hello jw! I’m your regular listener and subscriber. I’m just curious about why exactly 94w per hour? It could be per minute or per day, cause we calculate amps2 times resistance. We did not calculate about timing like hour or minute....
Watts isn't per anything - it's just 94 watts, or 94 joules per second.
got it. Thanks!
In AU standard electrical cable is i am pretty sure 2.5mm squared. Would that be because the higher voltage of 240V helps it? Also does stranded or solid copper wire make a difference? Thanks
Australia uses 230V as the reference single phase voltage (with the + an - tolerance bands similar to the UK and Europe. 240v was the reference values many years ago). 2.5mm squared cable (protected by a 16A or 20A MCB) is the typical (which will vary depending on the installation conditions) cable size used for power circuits supplying sockets (radial wiring is used; ring finals are not used).
The voltage is the same as the UK and 2.5mm^2 cable can be used on radial circuits up to about 20A (although 16A is more usual).
In this case, a 7kW charger will draw about about 30A at the UK's nominal 230V (typically closer to 240V as the EU spec is 230V +10%/-6% and the UK system is run closer to the top end). In theory, a 120V 7kW charger would draw about 60A, but nobody does that anywhere in the world that I know of. In North America a 7kW charger will be run at 240V, just like all their high powered devices, and not the 120V or the "standard" outlets (the USA uses a 240V split-phase system in properties).
Good day JW, please I'd appreciate your technical assistance with a technical question.
1. What is the cause (s) of negative power factor
2. How can it be corrected
I have often wondered whether the supplies will cope when electric vehicles are in universal usage. With the exception of supplies to premises using storage heaters, which need to supply f.l.c., in general the diversity allows for about 3kw per household - this is the case in my area, which is rural and supplied by overhead lines. A section was recently changed to aerial bundled, and one of the engineers told me that the substation fuses were being uprated to 300 amps: given the number of dwellings supplied by the distributing main, this equates to around 3kw per dwelling. I would expect that if economy seven is still available, many users will switch to this, and charge their vehicles during the off peak period, thus exacerbating the problem.
this is why i paid extra £99 for a 7kw ev charger even though my car charges at 3.6kw as it it more efficient for the last 4 years use and is future proofed for more capacity too
For what it's worth, the US standard for an ampacity of 30 A would be 10 AWG, which Google claims is 6 mm², right in the middle of your examples.
Rather a handy example, since my metal lathe pulls 30A@240VAC. Not really liking that 63W dissipation, although I don't think I ever run the lathe at anything close to full power consumption.
Yet another reason to use type S cable and not SJ.
a 7kW motor on a lathe? That's a lot of power, although bear in mind that electric motors draw much less power unless under very heavy load, and I suspect that the average current pull will be much less most of the time.
Demonstrates just one reason that I have always regarded tabulated values in the wiring regs as the Minimum specification. Often definitely Not the best, but often the cheapest.
Answer this question for me if you know?why in england dutch germany we use curve b and in france italy we use curve c,What is the use of the 1p + n circuit breaker,
and why monopolar circuit breakers are used in some countries and in others 1p + n?
Maybe make some videos about these topics
Hi John....In the original calculation determining the cable loss in Watts, how have you determined that this loss is per hour, and not per minute or second ?...in order to do the second, KWH calculation.
O.K. on the resistance per mtr...etc...but, where does it state....or where can I find out, if it takes an hour for this power loss to occur, in any of the guidance books?
One would presume, that if the circuit is using the full 32Amp, as suggested, the loss in power in the cable, is occuring every moment that the load is connected, after the cable reaches maximum temperature and resistance......based on this presumtion...the cable must be losing (x) amount of watts per second.
'watts per second' or per anything else is not valid - watts is the amount of power, and already includes the time unit (1 watt is 1 joule per second), and is the rate at which energy is transferred, in this case energy transferred from the cable into the surrounding environment.
kWh is used for the price calculation as that is how electricity is sold, that is just 1000 watts for one hour, or others such as 500 watts for 2 hours, 4000 watts for 15 minutes.
@@jwflame Thanks for the confirmation....I was debating the exact Joule theory earlier today....along with Coulombs etc....with a young college guy.
Watts are a unit of power, which is units of energy per second (Joules per second). A kWh is a unit of energy as we multiply by time. A kWh is 1000 joules per second (a kW) multiplied by 3,600 seconds, or 3.6 mega-Joules of energy. That's roughly the energy in 36 teaspoons of sugar.
I enjoyed that very much... Was just wondering what price you pay in the UK at night for electricity...
About 11pence /kw
Most of us in the UK will be on a standard single fixed rate (around 13-16p KWh at the moment), independent of the time of day. Saying that all of the electricity companies split the charge into what they call a daily standby charge which is a flat rate daily fee, which you pay even if you were to use no energy, plus a per unit cost based on actual usage. Historically, most people on a dual rate (called Economy 7 or 10) will be so only because they have electric storage heaters. I think this is a lot less common setup than it was 10-20 years ago as for most people the saving is minimal as the the utility companies increase the cost of the peak rate (see here www.moneysavingexpert.com/utilities/economy-7).
Although cheaper night electricity is still available (E7 or E10), it usually has the penalty that daytime units cost more, so unless the majority of use is at night, it's rarely worthwhile compared to a single 24h rate.
@@jwflame thanks John. That sounds like it might be another video in itself :)
@@grahamejones3036 still quite cheap compared to Germany, we pay up to about 30 cents per kWh. Which makes my hot water very expensive :-(
Just the mathematics I need to go over power loss in the cable.
Cable IR loss/wastage is relative!!.. If you live in a cold area and that most of that cable is inside the walls, then all that heat is recovered to heat your house. In fact since the temperature is a setting that require watts, then the cable heat "loss" is substracted from the watt of heat required to meet the temperature target of your home. same thing for the incandescent bulb.
It doesn't, because this is full rate electricity. Your house heating will almost certainly be cheaper (gas, oil or economy 7). The heating (in winter) helps a bit, but this is an expensive form of heating, the same way that incandescent light bulbs are an expensive form of heating.
Only true for colder times of the year, and even then it's a horrid way of heating, as cables aren't likely to be in a suitable location to heat the building, and direct electric heating is the most expensive option available.
@@seprishere Depend on your electricity rate.. here it's 6 cent per kWh as we have 99% hydro electricity. The "wasted" heat of incadescent bulb does not cost alot at 15 cent price per bulb for 2000 hours.. and does not pollute like oil or gas!. cable loss is something that is part of what an electrical cable is.. unless you are supraconducting these! so.. that heat cost nothing as in one way or another it will be part of teh equation.. In canada, heating home cost alot doring winter!! btw i did not talked about replacing the standard heating for light bulb! i talked about the fact that the heat loss in electricity can be part of what contribute to heating your home. take all that heat outdoor it will just cost more to heat your home.. so the fact that that heat is inside is adding to the heat source your home use.
Doctorbass you might be in the lucky position that there isn’t much running cost difference between incandescent lamps and LED equivalents. Ditto for pollution. But they still consume a factor of 5 - 10 times as much energy. Imagine if ALL Canadian lights were changed to LED. That’d be a massive chunk of power NOT drained from your system. So even fewer fossil fuel power stations would be needed.
My brain gave up slightly but I'm fairly sure if current delivered through each cable is constant the power supplied to the vehicle in this case would be slightly less for the smaller cross section cable therefore would require an extra 31 watts delivered to give same charge and that would also add up over time. It is too late on a Sunday to even consider checking this.
Just buy the 10. If you give up charging, the cable still has value.
Yes this is basically correct. The charger is a switch mode converter which takes a fixed amount of power regardless of input voltage. So using a larger csa cable will increase the voltage at the converter input which will cause it to take less current which makes the energy cost saving even greater. As others have mentioned using thicker cable also reduces the temperature of the cable which reduces the resistivity of the copper which also increases the cost reduction.
Because many use bipolar circuit breakers because they are afraid of
if the energy supplier reverses the phase with zero and you have a monopolar circuit breaker the phase will come to zero and there is no monopolar protection
DC Surge protection on PV DC cables?
That's a lot of power! Almost as bad as the ultra-cheap extension leads which set on fire when given more than an amp or so of current. At very least, it's a non-energy saving light bulb wasted.
Having said that, I have to use a wasteful light bulb in my bedroom light, because the lamp is a dimmer with three settings plus off. I have tried an LED and it works but doesn't dim (it's on or off) and other LEDs might not work.
Also, in winter, the heat might actually be useful, though even then it is full rate electricity rather than gas or economy 7. Maybe that is a factor?
You can buy dimmable LED bulbs.
@@UCCLdIk6R5ECGtaGm7oqO-TQ Not conveniently, though I think the IKEA ones are.
@@seprishere Screwfix sell dimmable LEDs for a few pounds.
@@UCCLdIk6R5ECGtaGm7oqO-TQ You also have to have a dimmer that works with dimmable LEDs, and not all do.
And what is the voltage drop if we applying a load of 32A on 4mm cable? Plz answer me
Depends on the length of the cable.
Sir let lengths is 100m plz sir give me answer
@@godgameplay2361 Approximately 30 volts, which is far too high. A 32A load on a 100m cable will require a much larger size of conductor.
@@jwflame thanku so much can you suggest me the what the size be? Plz
Hi, John. I just passed my 18Th edition test but there was a question which I could not answer: Here it is: how long will it take 6 mm square cable in 90 degree ambient air to reach 160 degree? if you could help to answer this please?
It never will without knowing the rest of the queastion.
You need to know the thermal mass of the cable and the thermal conductivity to the atmosphere to answer that. You might be able to find that in standard references, however.
@@UberAlphaSirus I am sorry. but this is exactly the question. no further information was given. May be what I forgot was to mention that it was a copper conductor.
@@PaulSteMarie Can you these information on the 18TH edition?
The question is meaningless without knowing what other variables are at play (e.g. current load, installation method, cable type, etc).
Cables within the house in the winter is not waste energy.
Gets more complicated when the cabling is within the house and it has electric heating... (my argument against the demonization of incansescent lamps). I use LED's almost exclusively but... there ARE circumstances where it's not a problem
By coincidence I've been doing exactly the same calculation for installing a cable to my garage for my new old Oxford Bantam 180 welder.
1:23 thro to 1:43 JW speaking Italian.
Kwh / kw whats is the diferenc.
kW = power
kWh = power for a certain amount of time.
@@jwflame thanks
Cables can be sold later, metal prices go up, it's an investment!
I now look at my Cooker with a frown wondering if it is wasting my Electricity ...
But it’s only on for an hour or less most days, so the losses are less than a fith of the ev charger. To put it another way, it’d take 15yrs to break even rather than 3 yrs.
Whatever cable u use, it WILL be loosing SOMETHING, because no cable has zero resistance.
missing is the fact that today more and more power consumption is from higly inductive loads and switch mode psu's , so all these calculations would be quite under rated ...not to mention car charging , power factors are very poor !!
You also get 60W more charging, so the car is charged quicker. Its less than 1 percent, but its a cheap upgrade.
you are much cheaper using 10mm cable much less waste. It would pay for itself over the years. our charging point would be near the consumer unit. about 3 metre of cable would be needed.
Be careful when using this as logic for designing for maximum conductor size as theoretical voltage drop mitigation & associated savings are really difficult to recoup particularly when in a domestic environment even for the sustained-power output of EV chargers. The engineer in me wants to install the fattest cable for our next EV charger at a holiday home but running the calculations on real world use - it just doesn’t hold water if your sole aim is to invest in 10 or 16mm cable just to save money. Yes EV chargers spec sheets do design for 16mm conductor sizing! Fair enough if you have a long run and need to hit minimum voltage drop parameters but you wont be saving money anytime in the next decade (or maybe 2) for doing so, its purely for performance in that scenario.
For reference my long established (>3 year) average energy consumption in hatchback EV is 18.1kWh/100km in an suburban setting with occasional motorway driving ~130km/h and Irish weather (temperate climate, mostly mild & always wet 😂) much like yours in the UK. Price of energy is 0.31€/kWh (which is essentially a market low here), best T&E prices I can find are 16mm cable at 9.4€/m, 10mm at 6€/m and 6mm at 4€/m. For reference I drive ~18k/km a year meaning I charger for less than 500 hours a year. The example here is 1250hours.
If you run an office fleet of cars perpetually charging on 7kW AC then you may actually reach a ROI. Although in that case perhaps you’d be using 3 phase 11-22kW AC so much of this domestic scenario won’t apply. Best I can tell - 6mm is probably the sweetspot between overkill and minimised energy wastage in the context of the cost of copper for most homes. To be fair I think that was the logical conclusion from this video. Perhaps you can find better cable pricing but to be honest you’d also probably be paying for higher spec EV-Ultra style cable (SWA with Cat5 ethernet) and that’s what most Electricians will go with.
Really enjoyed this video, always learn a tonne from your content. Open to discussion & challenge on this. 👍
Thank you. I wish if you speak slower haha. Thank you Sir.
The playback speed can generally be changed by clicking Cog Wheel Icon sited at the very bottom right side of the screen that is showing your chosen video.
John, can I thank you for sorting out the intonation of your speech. I'm currently watching a video of yours on ring circuits from 2016 and your intonation is 'quiet quiet quiet quiet quiet LOUD LOUD' for every sentence. it's frustratingly annoying.
I've not noticed that in any of his videos. Was it really necessary to write this, and in such an unpleasant manner?